| 0/0 |
2026/05/25 23:32 |
flow |
assessment-security |
42m
Results: map[DenialOfService:true Explanation:**Bug Analysis:**
The crash is caused by an out-of-bounds write in the JFS filesystem's directory
entry insertion code (`dtInsertEntry`).
When a new file is created in a JFS directory, `jfs_create` calls `dtInsert`,
which then calls `dtInsertEntry` to add the new entry to the directory. If the
parent directory is an inline directory (its data is stored directly within the
inode's `jfs_inode_info` structure), `dtInsertEntry` allocates a free slot using
the directory's internal freelist (`p->header.freelist`).
However, there is no bounds checking on the `freelist` index. If a crafted JFS
image is mounted, an attacker can supply a corrupted inline directory with a
`freelist` index that points outside the bounds of the inline directory array
(`dtroot_t`, which only has 9 slots). Because the inline directory is embedded
within the `jfs_inode_info` structure, an out-of-bounds slot index causes
`dtInsertEntry` to write the new file's name into adjacent fields of the
`jfs_inode_info` structure, or even past the end of the structure into adjacent
slab objects.
In the provided crash report, the `freelist` index was crafted such that the
filename (`cpuacct.usage_percpu`) was written over the `vfs_inode->i_sb`
pointer. The filename is converted to UTF-16LE, and the substring "rcpu" (which
is `72 00 63 00 70 00 75 00` in hex) overwrote the `i_sb` pointer. When
`inode_set_ctime_current` subsequently tried to access
`inode->i_sb->s_time_gran`, it dereferenced this wild pointer
(`0x0075007000630812`), causing a General Protection Fault.
**Security Impact:**
* **Exploitable:** Yes. This is a highly exploitable buffer overflow. An
attacker controls both the offset (via the `freelist` index) and the data (via
the filename). Although the data is converted to UTF-16LE (meaning every odd
byte is `0x00` if no NLS table is used), the attacker can still overwrite
critical fields. For example, they can overwrite the `i_uid` or `i_gid` of
adjacent inodes in the slab cache (since slab caches are often merged),
potentially granting themselves ownership of sensitive files belonging to other
filesystems. They could also overwrite `i_size` to cause out-of-bounds
reads/writes, or corrupt function pointers if they can bypass SMAP.
* **Denial of Service:** Yes. Triggering the bug easily leads to a kernel
panic/crash.
* **Accessible From Unprivileged Processes / User Namespaces:** No. The JFS
filesystem does not have the `FS_USERNS_MOUNT` flag. Therefore, an unprivileged
user cannot mount a crafted JFS image directly, not even within a user
namespace. It requires `CAP_SYS_ADMIN` in the initial namespace.
* **Malicious Filesystem / Peripheral Trigger:** Yes. The bug can be triggered
if the system is configured to auto-mount external media (e.g., plugging in a
USB drive with a crafted JFS image on a Linux desktop environment running
`udisks2`). Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/05/25 23:32 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <setjmp.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/loop.h>
#ifndef __NR_memfd_create
#define __NR_memfd_create 319
#endif
static unsigned long long procid;
//% This code is derived from puff.{c,h}, found in the zlib development. The
//% original files come with the following copyright notice:
//% Copyright (C) 2002-2013 Mark Adler, all rights reserved
//% version 2.3, 21 Jan 2013
//% This software is provided 'as-is', without any express or implied
//% warranty. In no event will the author be held liable for any damages
//% arising from the use of this software.
//% Permission is granted to anyone to use this software for any purpose,
//% including commercial applications, and to alter it and redistribute it
//% freely, subject to the following restrictions:
//% 1. The origin of this software must not be misrepresented; you must not
//% claim that you wrote the original software. If you use this software
//% in a product, an acknowledgment in the product documentation would be
//% appreciated but is not required.
//% 2. Altered source versions must be plainly marked as such, and must not be
//% misrepresented as being the original software.
//% 3. This notice may not be removed or altered from any source distribution.
//% Mark Adler madler@alumni.caltech.edu
//% BEGIN CODE DERIVED FROM puff.{c,h}
#define MAXBITS 15
#define MAXLCODES 286
#define MAXDCODES 30
#define MAXCODES (MAXLCODES + MAXDCODES)
#define FIXLCODES 288
struct puff_state {
unsigned char* out;
unsigned long outlen;
unsigned long outcnt;
const unsigned char* in;
unsigned long inlen;
unsigned long incnt;
int bitbuf;
int bitcnt;
jmp_buf env;
};
static int puff_bits(struct puff_state* s, int need)
{
long val = s->bitbuf;
while (s->bitcnt < need) {
if (s->incnt == s->inlen)
longjmp(s->env, 1);
val |= (long)(s->in[s->incnt++]) << s->bitcnt;
s->bitcnt += 8;
}
s->bitbuf = (int)(val >> need);
s->bitcnt -= need;
return (int)(val & ((1L << need) - 1));
}
static int puff_stored(struct puff_state* s)
{
s->bitbuf = 0;
s->bitcnt = 0;
if (s->incnt + 4 > s->inlen)
return 2;
unsigned len = s->in[s->incnt++];
len |= s->in[s->incnt++] << 8;
if (s->in[s->incnt++] != (~len & 0xff) ||
s->in[s->incnt++] != ((~len >> 8) & 0xff))
return -2;
if (s->incnt + len > s->inlen)
return 2;
if (s->outcnt + len > s->outlen)
return 1;
for (; len--; s->outcnt++, s->incnt++) {
if (s->in[s->incnt])
s->out[s->outcnt] = s->in[s->incnt];
}
return 0;
}
struct puff_huffman {
short* count;
short* symbol;
};
static int puff_decode(struct puff_state* s, const struct puff_huffman* h)
{
int first = 0;
int index = 0;
int bitbuf = s->bitbuf;
int left = s->bitcnt;
int code = first = index = 0;
int len = 1;
short* next = h->count + 1;
while (1) {
while (left--) {
code |= bitbuf & 1;
bitbuf >>= 1;
int count = *next++;
if (code - count < first) {
s->bitbuf = bitbuf;
s->bitcnt = (s->bitcnt - len) & 7;
return h->symbol[index + (code - first)];
}
index += count;
first += count;
first <<= 1;
code <<= 1;
len++;
}
left = (MAXBITS + 1) - len;
if (left == 0)
break;
if (s->incnt == s->inlen)
longjmp(s->env, 1);
bitbuf = s->in[s->incnt++];
if (left > 8)
left = 8;
}
return -10;
}
static int puff_construct(struct puff_huffman* h, const short* length, int n)
{
int len;
for (len = 0; len <= MAXBITS; len++)
h->count[len] = 0;
int symbol;
for (symbol = 0; symbol < n; symbol++)
(h->count[length[symbol]])++;
if (h->count[0] == n)
return 0;
int left = 1;
for (len = 1; len <= MAXBITS; len++) {
left <<= 1;
left -= h->count[len];
if (left < 0)
return left;
}
short offs[MAXBITS + 1];
offs[1] = 0;
for (len = 1; len < MAXBITS; len++)
offs[len + 1] = offs[len] + h->count[len];
for (symbol = 0; symbol < n; symbol++)
if (length[symbol] != 0)
h->symbol[offs[length[symbol]]++] = symbol;
return left;
}
static int puff_codes(struct puff_state* s,
const struct puff_huffman* lencode,
const struct puff_huffman* distcode)
{
static const short lens[29] = {
3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258};
static const short lext[29] = {
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0};
static const short dists[30] = {
1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
8193, 12289, 16385, 24577};
static const short dext[30] = {
0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
7, 7, 8, 8, 9, 9, 10, 10, 11, 11,
12, 12, 13, 13};
int symbol;
do {
symbol = puff_decode(s, lencode);
if (symbol < 0)
return symbol;
if (symbol < 256) {
if (s->outcnt == s->outlen)
return 1;
if (symbol)
s->out[s->outcnt] = symbol;
s->outcnt++;
} else if (symbol > 256) {
symbol -= 257;
if (symbol >= 29)
return -10;
int len = lens[symbol] + puff_bits(s, lext[symbol]);
symbol = puff_decode(s, distcode);
if (symbol < 0)
return symbol;
unsigned dist = dists[symbol] + puff_bits(s, dext[symbol]);
if (dist > s->outcnt)
return -11;
if (s->outcnt + len > s->outlen)
return 1;
while (len--) {
if (dist <= s->outcnt && s->out[s->outcnt - dist])
s->out[s->outcnt] = s->out[s->outcnt - dist];
s->outcnt++;
}
}
} while (symbol != 256);
return 0;
}
static int puff_fixed(struct puff_state* s)
{
static int virgin = 1;
static short lencnt[MAXBITS + 1], lensym[FIXLCODES];
static short distcnt[MAXBITS + 1], distsym[MAXDCODES];
static struct puff_huffman lencode, distcode;
if (virgin) {
lencode.count = lencnt;
lencode.symbol = lensym;
distcode.count = distcnt;
distcode.symbol = distsym;
short lengths[FIXLCODES];
int symbol;
for (symbol = 0; symbol < 144; symbol++)
lengths[symbol] = 8;
for (; symbol < 256; symbol++)
lengths[symbol] = 9;
for (; symbol < 280; symbol++)
lengths[symbol] = 7;
for (; symbol < FIXLCODES; symbol++)
lengths[symbol] = 8;
puff_construct(&lencode, lengths, FIXLCODES);
for (symbol = 0; symbol < MAXDCODES; symbol++)
lengths[symbol] = 5;
puff_construct(&distcode, lengths, MAXDCODES);
virgin = 0;
}
return puff_codes(s, &lencode, &distcode);
}
static int puff_dynamic(struct puff_state* s)
{
static const short order[19] =
{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
int nlen = puff_bits(s, 5) + 257;
int ndist = puff_bits(s, 5) + 1;
int ncode = puff_bits(s, 4) + 4;
if (nlen > MAXLCODES || ndist > MAXDCODES)
return -3;
short lengths[MAXCODES];
int index;
for (index = 0; index < ncode; index++)
lengths[order[index]] = puff_bits(s, 3);
for (; index < 19; index++)
lengths[order[index]] = 0;
short lencnt[MAXBITS + 1], lensym[MAXLCODES];
struct puff_huffman lencode = {lencnt, lensym};
int err = puff_construct(&lencode, lengths, 19);
if (err != 0)
return -4;
index = 0;
while (index < nlen + ndist) {
int symbol;
int len;
symbol = puff_decode(s, &lencode);
if (symbol < 0)
return symbol;
if (symbol < 16)
lengths[index++] = symbol;
else {
len = 0;
if (symbol == 16) {
if (index == 0)
return -5;
len = lengths[index - 1];
symbol = 3 + puff_bits(s, 2);
} else if (symbol == 17)
symbol = 3 + puff_bits(s, 3);
else
symbol = 11 + puff_bits(s, 7);
if (index + symbol > nlen + ndist)
return -6;
while (symbol--)
lengths[index++] = len;
}
}
if (lengths[256] == 0)
return -9;
err = puff_construct(&lencode, lengths, nlen);
if (err && (err < 0 || nlen != lencode.count[0] + lencode.count[1]))
return -7;
short distcnt[MAXBITS + 1], distsym[MAXDCODES];
struct puff_huffman distcode = {distcnt, distsym};
err = puff_construct(&distcode, lengths + nlen, ndist);
if (err && (err < 0 || ndist != distcode.count[0] + distcode.count[1]))
return -8;
return puff_codes(s, &lencode, &distcode);
}
static int puff(
unsigned char* dest,
unsigned long* destlen,
const unsigned char* source,
unsigned long sourcelen)
{
struct puff_state s = {
.out = dest,
.outlen = *destlen,
.outcnt = 0,
.in = source,
.inlen = sourcelen,
.incnt = 0,
.bitbuf = 0,
.bitcnt = 0,
};
int err;
if (setjmp(s.env) != 0)
err = 2;
else {
int last;
do {
last = puff_bits(&s, 1);
int type = puff_bits(&s, 2);
err = type == 0 ? puff_stored(&s) : (type == 1 ? puff_fixed(&s) : (type == 2 ? puff_dynamic(&s) : -1));
if (err != 0)
break;
} while (!last);
}
*destlen = s.outcnt;
return err;
}
//% END CODE DERIVED FROM puff.{c,h}
#define ZLIB_HEADER_WIDTH 2
static int puff_zlib_to_file(const unsigned char* source, unsigned long sourcelen, int dest_fd)
{
if (sourcelen < ZLIB_HEADER_WIDTH)
return 0;
source += ZLIB_HEADER_WIDTH;
sourcelen -= ZLIB_HEADER_WIDTH;
const unsigned long max_destlen = 132 << 20;
void* ret = mmap(0, max_destlen, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
if (ret == MAP_FAILED)
return -1;
unsigned char* dest = (unsigned char*)ret;
unsigned long destlen = max_destlen;
int err = puff(dest, &destlen, source, sourcelen);
if (err) {
munmap(dest, max_destlen);
errno = -err;
return -1;
}
if (write(dest_fd, dest, destlen) != (ssize_t)destlen) {
munmap(dest, max_destlen);
return -1;
}
return munmap(dest, max_destlen);
}
static int setup_loop_device(unsigned char* data, unsigned long size, const char* loopname, int* loopfd_p)
{
int err = 0, loopfd = -1;
int memfd = syscall(__NR_memfd_create, "syzkaller", 0);
if (memfd == -1) {
err = errno;
goto error;
}
if (puff_zlib_to_file(data, size, memfd)) {
err = errno;
goto error_close_memfd;
}
loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
err = errno;
goto error_close_memfd;
}
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
if (errno != EBUSY) {
err = errno;
goto error_close_loop;
}
ioctl(loopfd, LOOP_CLR_FD, 0);
usleep(1000);
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
err = errno;
goto error_close_loop;
}
}
close(memfd);
*loopfd_p = loopfd;
return 0;
error_close_loop:
close(loopfd);
error_close_memfd:
close(memfd);
error:
errno = err;
return -1;
}
static void reset_loop_device(const char* loopname)
{
int loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
return;
}
if (ioctl(loopfd, LOOP_CLR_FD, 0)) {
}
close(loopfd);
}
static long syz_mount_image(
volatile long fsarg,
volatile long dir,
volatile long flags,
volatile long optsarg,
volatile long change_dir,
volatile unsigned long size,
volatile long image)
{
unsigned char* data = (unsigned char*)image;
int res = -1, err = 0, need_loop_device = !!size;
char* mount_opts = (char*)optsarg;
char* target = (char*)dir;
char* fs = (char*)fsarg;
char* source = NULL;
char loopname[64];
if (need_loop_device) {
int loopfd;
memset(loopname, 0, sizeof(loopname));
snprintf(loopname, sizeof(loopname), "/dev/loop%llu", procid);
if (setup_loop_device(data, size, loopname, &loopfd) == -1)
return -1;
close(loopfd);
source = loopname;
}
mkdir(target, 0777);
char opts[256];
memset(opts, 0, sizeof(opts));
if (strlen(mount_opts) > (sizeof(opts) - 32)) {
}
strncpy(opts, mount_opts, sizeof(opts) - 32);
if (strcmp(fs, "iso9660") == 0) {
flags |= MS_RDONLY;
} else if (strncmp(fs, "ext", 3) == 0) {
bool has_remount_ro = false;
char* remount_ro_start = strstr(opts, "errors=remount-ro");
if (remount_ro_start != NULL) {
char after = *(remount_ro_start + strlen("errors=remount-ro"));
char before = remount_ro_start == opts ? '\0' : *(remount_ro_start - 1);
has_remount_ro = ((before == '\0' || before == ',') && (after == '\0' || after == ','));
}
if (strstr(opts, "errors=panic") || !has_remount_ro)
strcat(opts, ",errors=continue");
} else if (strcmp(fs, "xfs") == 0) {
strcat(opts, ",nouuid");
} else if (strncmp(fs, "gfs2", 4) == 0 && (strstr(opts, "errors=panic") || strstr(opts, "debug"))) {
strcat(opts, ",errors=withdraw");
}
res = mount(source, target, fs, flags, opts);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
res = open(target, O_RDONLY | O_DIRECTORY);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
if (change_dir) {
res = chdir(target);
if (res == -1) {
err = errno;
}
}
error_clear_loop:
if (need_loop_device)
reset_loop_device(loopname);
errno = err;
return res;
}
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// syz_mount_image$jfs arguments: [
// fs: ptr[in, buffer] {
// buffer: {6a 66 73 00} (length 0x4)
// }
// dir: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 30 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 00} (length 0xfb)
// }
// flags: mount_flags = 0x1c802 (8 bytes)
// opts: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// }
// }
// chdir: int8 = 0x1 (1 bytes)
// size: len = 0x6003 (8 bytes)
// img: ptr[in, buffer] {
// buffer: (compressed buffer with length 0x6003)
// }
// ]
// returns fd_dir
memcpy((void*)0x200000000400, "jfs\000", 4);
memcpy((void*)0x200000012ec0, "... [truncated large byte array] ...", 251);
memcpy((void*)0x200000012fc0, "... [truncated large byte array] ...", 24579);
syz_mount_image(/*fs=*/0x200000000400, /*dir=*/0x200000012ec0, /*flags=MS_POSIXACL|MS_REC|MS_SILENT|MS_NOSUID|MS_NODIRATIME*/0x1c802, /*opts=*/0x200000002740, /*chdir=*/1, /*size=*/0x6003, /*img=*/0x200000012fc0);
// openat$cgroup_ro arguments: [
// fd: fd_cgroup (resource)
// file: ptr[in, buffer] {
// buffer: {63 70 75 61 63 63 74 2e 75 73 61 67 65 5f 70 65 72 63 70 75 00} (length 0x15)
// }
// flags: const = 0x275a (4 bytes)
// mode: const = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000140, "cpuacct.usage_percpu\000", 21);
syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000140ul, /*flags=*/0x275a, /*mode=*/0);
return 0;
}
]
|
| 2/1 |
2026/05/25 23:32 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/6cb2e6561db479b2fb5d97db3b1e81fb3573f2f8]
|
| 3/1 |
2026/05/25 23:33 |
action |
kernel-builder |
14m
Results: map[KernelObj:/app/workdir/cache/build/49e0e8cc5a5b72a2cba297789999132c60584ef4]
|
| 4/1 |
2026/05/25 23:48 |
action |
codesearch-prepare |
19m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/26 00:08 |
agent |
expert |
7m
Model:
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Instruction:
You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by greeping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completly wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control tranfers, that's also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitabability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidetial Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
loop0: detected capacity change from 0 to 32768
Oops: general protection fault, probably for non-canonical address 0xe00e9c0e000c6102: 0000 [#1] SMP KASAN PTI
KASAN: maybe wild-memory-access in range [0x0075007000630810-0x0075007000630817]
CPU: 0 UID: 0 PID: 6077 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:timestamp_truncate fs/inode.c:2732 [inline]
RIP: 0010:inode_set_ctime_current+0xcf/0xb40 fs/inode.c:2774
Code: d8 48 c1 e8 03 48 89 44 24 30 42 80 3c 20 00 74 08 48 89 df e8 92 fc eb ff 4c 8b 3b 49 8d bf a0 07 00 00 48 89 f8 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 d6 07 00 00 48 89 5c 24 20 41 8b 87 a0
RSP: 0018:ffffc900047475a0 EFLAGS: 00010202
RAX: 000ea00e000c6102 RBX: ffff8880526f3528 RCX: ffff88803afdda00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0075007000630812
RBP: ffffc90004747690 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1dac52f R12: dffffc0000000000
R13: ffff8880526f4258 R14: ffffc90004747600 R15: 0075007000630072
FS: 000055556de63500(0000) GS:ffff888126dfc000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2ff63fff CR3: 00000000382fc000 CR4: 00000000003526f0
Call Trace:
<TASK>
jfs_create+0x7f7/0xa80 fs/jfs/namei.c:152
lookup_open fs/namei.c:3796 [inline]
open_last_lookups fs/namei.c:3895 [inline]
path_openat+0x1500/0x3840 fs/namei.c:4131
do_filp_open+0x1fa/0x410 fs/namei.c:4161
do_sys_openat2+0x121/0x1c0 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_openat fs/open.c:1468 [inline]
__se_sys_openat fs/open.c:1463 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1463
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fba988befc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff4fe1f1e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fba98b15fa0 RCX: 00007fba988befc9
RDX: 000000000000275a RSI: 0000200000000140 RDI: ffffffffffffff9c
RBP: 00007fba98941f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fba98b15fa0 R14: 00007fba98b15fa0 R15: 0000000000000004
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:timestamp_truncate fs/inode.c:2732 [inline]
RIP: 0010:inode_set_ctime_current+0xcf/0xb40 fs/inode.c:2774
Code: d8 48 c1 e8 03 48 89 44 24 30 42 80 3c 20 00 74 08 48 89 df e8 92 fc eb ff 4c 8b 3b 49 8d bf a0 07 00 00 48 89 f8 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 d6 07 00 00 48 89 5c 24 20 41 8b 87 a0
RSP: 0018:ffffc900047475a0 EFLAGS: 00010202
RAX: 000ea00e000c6102 RBX: ffff8880526f3528 RCX: ffff88803afdda00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0075007000630812
RBP: ffffc90004747690 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1dac52f R12: dffffc0000000000
R13: ffff8880526f4258 R14: ffffc90004747600 R15: 0075007000630072
FS: 000055556de63500(0000) GS:ffff888126dfc000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2ff63fff CR3: 00000000382fc000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: d8 48 c1 fmuls -0x3f(%rax)
3: e8 03 48 89 44 call 0x4489480b
8: 24 30 and $0x30,%al
a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1)
f: 74 08 je 0x19
11: 48 89 df mov %rbx,%rdi
14: e8 92 fc eb ff call 0xffebfcab
19: 4c 8b 3b mov (%rbx),%r15
1c: 49 8d bf a0 07 00 00 lea 0x7a0(%r15),%rdi
23: 48 89 f8 mov %rdi,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 0f b6 04 20 movzbl (%rax,%r12,1),%eax <-- trapping instruction
2f: 84 c0 test %al,%al
31: 0f 85 d6 07 00 00 jne 0x80d
37: 48 89 5c 24 20 mov %rbx,0x20(%rsp)
3c: 41 rex.B
3d: 8b .byte 0x8b
3e: 87 .byte 0x87
3f: a0 .byte 0xa0
It is reproducible with the followint program.
Keep in mind that it may lack the precise threading, sandboxing, and some arguments of a working reproducer.
But it should give an idea of the involved syscalls.
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <setjmp.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/loop.h>
#ifndef __NR_memfd_create
#define __NR_memfd_create 319
#endif
static unsigned long long procid;
//% This code is derived from puff.{c,h}, found in the zlib development. The
//% original files come with the following copyright notice:
//% Copyright (C) 2002-2013 Mark Adler, all rights reserved
//% version 2.3, 21 Jan 2013
//% This software is provided 'as-is', without any express or implied
//% warranty. In no event will the author be held liable for any damages
//% arising from the use of this software.
//% Permission is granted to anyone to use this software for any purpose,
//% including commercial applications, and to alter it and redistribute it
//% freely, subject to the following restrictions:
//% 1. The origin of this software must not be misrepresented; you must not
//% claim that you wrote the original software. If you use this software
//% in a product, an acknowledgment in the product documentation would be
//% appreciated but is not required.
//% 2. Altered source versions must be plainly marked as such, and must not be
//% misrepresented as being the original software.
//% 3. This notice may not be removed or altered from any source distribution.
//% Mark Adler madler@alumni.caltech.edu
//% BEGIN CODE DERIVED FROM puff.{c,h}
#define MAXBITS 15
#define MAXLCODES 286
#define MAXDCODES 30
#define MAXCODES (MAXLCODES + MAXDCODES)
#define FIXLCODES 288
struct puff_state {
unsigned char* out;
unsigned long outlen;
unsigned long outcnt;
const unsigned char* in;
unsigned long inlen;
unsigned long incnt;
int bitbuf;
int bitcnt;
jmp_buf env;
};
static int puff_bits(struct puff_state* s, int need)
{
long val = s->bitbuf;
while (s->bitcnt < need) {
if (s->incnt == s->inlen)
longjmp(s->env, 1);
val |= (long)(s->in[s->incnt++]) << s->bitcnt;
s->bitcnt += 8;
}
s->bitbuf = (int)(val >> need);
s->bitcnt -= need;
return (int)(val & ((1L << need) - 1));
}
static int puff_stored(struct puff_state* s)
{
s->bitbuf = 0;
s->bitcnt = 0;
if (s->incnt + 4 > s->inlen)
return 2;
unsigned len = s->in[s->incnt++];
len |= s->in[s->incnt++] << 8;
if (s->in[s->incnt++] != (~len & 0xff) ||
s->in[s->incnt++] != ((~len >> 8) & 0xff))
return -2;
if (s->incnt + len > s->inlen)
return 2;
if (s->outcnt + len > s->outlen)
return 1;
for (; len--; s->outcnt++, s->incnt++) {
if (s->in[s->incnt])
s->out[s->outcnt] = s->in[s->incnt];
}
return 0;
}
struct puff_huffman {
short* count;
short* symbol;
};
static int puff_decode(struct puff_state* s, const struct puff_huffman* h)
{
int first = 0;
int index = 0;
int bitbuf = s->bitbuf;
int left = s->bitcnt;
int code = first = index = 0;
int len = 1;
short* next = h->count + 1;
while (1) {
while (left--) {
code |= bitbuf & 1;
bitbuf >>= 1;
int count = *next++;
if (code - count < first) {
s->bitbuf = bitbuf;
s->bitcnt = (s->bitcnt - len) & 7;
return h->symbol[index + (code - first)];
}
index += count;
first += count;
first <<= 1;
code <<= 1;
len++;
}
left = (MAXBITS + 1) - len;
if (left == 0)
break;
if (s->incnt == s->inlen)
longjmp(s->env, 1);
bitbuf = s->in[s->incnt++];
if (left > 8)
left = 8;
}
return -10;
}
static int puff_construct(struct puff_huffman* h, const short* length, int n)
{
int len;
for (len = 0; len <= MAXBITS; len++)
h->count[len] = 0;
int symbol;
for (symbol = 0; symbol < n; symbol++)
(h->count[length[symbol]])++;
if (h->count[0] == n)
return 0;
int left = 1;
for (len = 1; len <= MAXBITS; len++) {
left <<= 1;
left -= h->count[len];
if (left < 0)
return left;
}
short offs[MAXBITS + 1];
offs[1] = 0;
for (len = 1; len < MAXBITS; len++)
offs[len + 1] = offs[len] + h->count[len];
for (symbol = 0; symbol < n; symbol++)
if (length[symbol] != 0)
h->symbol[offs[length[symbol]]++] = symbol;
return left;
}
static int puff_codes(struct puff_state* s,
const struct puff_huffman* lencode,
const struct puff_huffman* distcode)
{
static const short lens[29] = {
3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258};
static const short lext[29] = {
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0};
static const short dists[30] = {
1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
8193, 12289, 16385, 24577};
static const short dext[30] = {
0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
7, 7, 8, 8, 9, 9, 10, 10, 11, 11,
12, 12, 13, 13};
int symbol;
do {
symbol = puff_decode(s, lencode);
if (symbol < 0)
return symbol;
if (symbol < 256) {
if (s->outcnt == s->outlen)
return 1;
if (symbol)
s->out[s->outcnt] = symbol;
s->outcnt++;
} else if (symbol > 256) {
symbol -= 257;
if (symbol >= 29)
return -10;
int len = lens[symbol] + puff_bits(s, lext[symbol]);
symbol = puff_decode(s, distcode);
if (symbol < 0)
return symbol;
unsigned dist = dists[symbol] + puff_bits(s, dext[symbol]);
if (dist > s->outcnt)
return -11;
if (s->outcnt + len > s->outlen)
return 1;
while (len--) {
if (dist <= s->outcnt && s->out[s->outcnt - dist])
s->out[s->outcnt] = s->out[s->outcnt - dist];
s->outcnt++;
}
}
} while (symbol != 256);
return 0;
}
static int puff_fixed(struct puff_state* s)
{
static int virgin = 1;
static short lencnt[MAXBITS + 1], lensym[FIXLCODES];
static short distcnt[MAXBITS + 1], distsym[MAXDCODES];
static struct puff_huffman lencode, distcode;
if (virgin) {
lencode.count = lencnt;
lencode.symbol = lensym;
distcode.count = distcnt;
distcode.symbol = distsym;
short lengths[FIXLCODES];
int symbol;
for (symbol = 0; symbol < 144; symbol++)
lengths[symbol] = 8;
for (; symbol < 256; symbol++)
lengths[symbol] = 9;
for (; symbol < 280; symbol++)
lengths[symbol] = 7;
for (; symbol < FIXLCODES; symbol++)
lengths[symbol] = 8;
puff_construct(&lencode, lengths, FIXLCODES);
for (symbol = 0; symbol < MAXDCODES; symbol++)
lengths[symbol] = 5;
puff_construct(&distcode, lengths, MAXDCODES);
virgin = 0;
}
return puff_codes(s, &lencode, &distcode);
}
static int puff_dynamic(struct puff_state* s)
{
static const short order[19] =
{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
int nlen = puff_bits(s, 5) + 257;
int ndist = puff_bits(s, 5) + 1;
int ncode = puff_bits(s, 4) + 4;
if (nlen > MAXLCODES || ndist > MAXDCODES)
return -3;
short lengths[MAXCODES];
int index;
for (index = 0; index < ncode; index++)
lengths[order[index]] = puff_bits(s, 3);
for (; index < 19; index++)
lengths[order[index]] = 0;
short lencnt[MAXBITS + 1], lensym[MAXLCODES];
struct puff_huffman lencode = {lencnt, lensym};
int err = puff_construct(&lencode, lengths, 19);
if (err != 0)
return -4;
index = 0;
while (index < nlen + ndist) {
int symbol;
int len;
symbol = puff_decode(s, &lencode);
if (symbol < 0)
return symbol;
if (symbol < 16)
lengths[index++] = symbol;
else {
len = 0;
if (symbol == 16) {
if (index == 0)
return -5;
len = lengths[index - 1];
symbol = 3 + puff_bits(s, 2);
} else if (symbol == 17)
symbol = 3 + puff_bits(s, 3);
else
symbol = 11 + puff_bits(s, 7);
if (index + symbol > nlen + ndist)
return -6;
while (symbol--)
lengths[index++] = len;
}
}
if (lengths[256] == 0)
return -9;
err = puff_construct(&lencode, lengths, nlen);
if (err && (err < 0 || nlen != lencode.count[0] + lencode.count[1]))
return -7;
short distcnt[MAXBITS + 1], distsym[MAXDCODES];
struct puff_huffman distcode = {distcnt, distsym};
err = puff_construct(&distcode, lengths + nlen, ndist);
if (err && (err < 0 || ndist != distcode.count[0] + distcode.count[1]))
return -8;
return puff_codes(s, &lencode, &distcode);
}
static int puff(
unsigned char* dest,
unsigned long* destlen,
const unsigned char* source,
unsigned long sourcelen)
{
struct puff_state s = {
.out = dest,
.outlen = *destlen,
.outcnt = 0,
.in = source,
.inlen = sourcelen,
.incnt = 0,
.bitbuf = 0,
.bitcnt = 0,
};
int err;
if (setjmp(s.env) != 0)
err = 2;
else {
int last;
do {
last = puff_bits(&s, 1);
int type = puff_bits(&s, 2);
err = type == 0 ? puff_stored(&s) : (type == 1 ? puff_fixed(&s) : (type == 2 ? puff_dynamic(&s) : -1));
if (err != 0)
break;
} while (!last);
}
*destlen = s.outcnt;
return err;
}
//% END CODE DERIVED FROM puff.{c,h}
#define ZLIB_HEADER_WIDTH 2
static int puff_zlib_to_file(const unsigned char* source, unsigned long sourcelen, int dest_fd)
{
if (sourcelen < ZLIB_HEADER_WIDTH)
return 0;
source += ZLIB_HEADER_WIDTH;
sourcelen -= ZLIB_HEADER_WIDTH;
const unsigned long max_destlen = 132 << 20;
void* ret = mmap(0, max_destlen, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
if (ret == MAP_FAILED)
return -1;
unsigned char* dest = (unsigned char*)ret;
unsigned long destlen = max_destlen;
int err = puff(dest, &destlen, source, sourcelen);
if (err) {
munmap(dest, max_destlen);
errno = -err;
return -1;
}
if (write(dest_fd, dest, destlen) != (ssize_t)destlen) {
munmap(dest, max_destlen);
return -1;
}
return munmap(dest, max_destlen);
}
static int setup_loop_device(unsigned char* data, unsigned long size, const char* loopname, int* loopfd_p)
{
int err = 0, loopfd = -1;
int memfd = syscall(__NR_memfd_create, "syzkaller", 0);
if (memfd == -1) {
err = errno;
goto error;
}
if (puff_zlib_to_file(data, size, memfd)) {
err = errno;
goto error_close_memfd;
}
loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
err = errno;
goto error_close_memfd;
}
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
if (errno != EBUSY) {
err = errno;
goto error_close_loop;
}
ioctl(loopfd, LOOP_CLR_FD, 0);
usleep(1000);
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
err = errno;
goto error_close_loop;
}
}
close(memfd);
*loopfd_p = loopfd;
return 0;
error_close_loop:
close(loopfd);
error_close_memfd:
close(memfd);
error:
errno = err;
return -1;
}
static void reset_loop_device(const char* loopname)
{
int loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
return;
}
if (ioctl(loopfd, LOOP_CLR_FD, 0)) {
}
close(loopfd);
}
static long syz_mount_image(
volatile long fsarg,
volatile long dir,
volatile long flags,
volatile long optsarg,
volatile long change_dir,
volatile unsigned long size,
volatile long image)
{
unsigned char* data = (unsigned char*)image;
int res = -1, err = 0, need_loop_device = !!size;
char* mount_opts = (char*)optsarg;
char* target = (char*)dir;
char* fs = (char*)fsarg;
char* source = NULL;
char loopname[64];
if (need_loop_device) {
int loopfd;
memset(loopname, 0, sizeof(loopname));
snprintf(loopname, sizeof(loopname), "/dev/loop%llu", procid);
if (setup_loop_device(data, size, loopname, &loopfd) == -1)
return -1;
close(loopfd);
source = loopname;
}
mkdir(target, 0777);
char opts[256];
memset(opts, 0, sizeof(opts));
if (strlen(mount_opts) > (sizeof(opts) - 32)) {
}
strncpy(opts, mount_opts, sizeof(opts) - 32);
if (strcmp(fs, "iso9660") == 0) {
flags |= MS_RDONLY;
} else if (strncmp(fs, "ext", 3) == 0) {
bool has_remount_ro = false;
char* remount_ro_start = strstr(opts, "errors=remount-ro");
if (remount_ro_start != NULL) {
char after = *(remount_ro_start + strlen("errors=remount-ro"));
char before = remount_ro_start == opts ? '\0' : *(remount_ro_start - 1);
has_remount_ro = ((before == '\0' || before == ',') && (after == '\0' || after == ','));
}
if (strstr(opts, "errors=panic") || !has_remount_ro)
strcat(opts, ",errors=continue");
} else if (strcmp(fs, "xfs") == 0) {
strcat(opts, ",nouuid");
} else if (strncmp(fs, "gfs2", 4) == 0 && (strstr(opts, "errors=panic") || strstr(opts, "debug"))) {
strcat(opts, ",errors=withdraw");
}
res = mount(source, target, fs, flags, opts);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
res = open(target, O_RDONLY | O_DIRECTORY);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
if (change_dir) {
res = chdir(target);
if (res == -1) {
err = errno;
}
}
error_clear_loop:
if (need_loop_device)
reset_loop_device(loopname);
errno = err;
return res;
}
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// syz_mount_image$jfs arguments: [
// fs: ptr[in, buffer] {
// buffer: {6a 66 73 00} (length 0x4)
// }
// dir: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 30 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 00} (length 0xfb)
// }
// flags: mount_flags = 0x1c802 (8 bytes)
// opts: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// }
// }
// chdir: int8 = 0x1 (1 bytes)
// size: len = 0x6003 (8 bytes)
// img: ptr[in, buffer] {
// buffer: (compressed buffer with length 0x6003)
// }
// ]
// returns fd_dir
memcpy((void*)0x200000000400, "jfs\000", 4);
memcpy((void*)0x200000012ec0, "... [truncated large byte array] ...", 251);
memcpy((void*)0x200000012fc0, "... [truncated large byte array] ...", 24579);
syz_mount_image(/*fs=*/0x200000000400, /*dir=*/0x200000012ec0, /*flags=MS_POSIXACL|MS_REC|MS_SILENT|MS_NOSUID|MS_NODIRATIME*/0x1c802, /*opts=*/0x200000002740, /*chdir=*/1, /*size=*/0x6003, /*img=*/0x200000012fc0);
// openat$cgroup_ro arguments: [
// fd: fd_cgroup (resource)
// file: ptr[in, buffer] {
// buffer: {63 70 75 61 63 63 74 2e 75 73 61 67 65 5f 70 65 72 63 70 75 00} (length 0x15)
// }
// flags: const = 0x275a (4 bytes)
// mode: const = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000140, "cpuacct.usage_percpu\000", 21);
syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000140ul, /*flags=*/0x275a, /*mode=*/0);
return 0;
}
Reply: **Bug Analysis:**
The crash is caused by an out-of-bounds write in the JFS filesystem's directory entry insertion code (`dtInsertEntry`).
When a new file is created in a JFS directory, `jfs_create` calls `dtInsert`, which then calls `dtInsertEntry` to add the new entry to the directory. If the parent directory is an inline directory (its data is stored directly within the inode's `jfs_inode_info` structure), `dtInsertEntry` allocates a free slot using the directory's internal freelist (`p->header.freelist`).
However, there is no bounds checking on the `freelist` index. If a crafted JFS image is mounted, an attacker can supply a corrupted inline directory with a `freelist` index that points outside the bounds of the inline directory array (`dtroot_t`, which only has 9 slots). Because the inline directory is embedded within the `jfs_inode_info` structure, an out-of-bounds slot index causes `dtInsertEntry` to write the new file's name into adjacent fields of the `jfs_inode_info` structure, or even past the end of the structure into adjacent slab objects.
In the provided crash report, the `freelist` index was crafted such that the filename (`cpuacct.usage_percpu`) was written over the `vfs_inode->i_sb` pointer. The filename is converted to UTF-16LE, and the substring "rcpu" (which is `72 00 63 00 70 00 75 00` in hex) overwrote the `i_sb` pointer. When `inode_set_ctime_current` subsequently tried to access `inode->i_sb->s_time_gran`, it dereferenced this wild pointer (`0x0075007000630812`), causing a General Protection Fault.
**Security Impact:**
* **Exploitable:** Yes. This is a highly exploitable buffer overflow. An attacker controls both the offset (via the `freelist` index) and the data (via the filename). Although the data is converted to UTF-16LE (meaning every odd byte is `0x00` if no NLS table is used), the attacker can still overwrite critical fields. For example, they can overwrite the `i_uid` or `i_gid` of adjacent inodes in the slab cache (since slab caches are often merged), potentially granting themselves ownership of sensitive files belonging to other filesystems. They could also overwrite `i_size` to cause out-of-bounds reads/writes, or corrupt function pointers if they can bypass SMAP.
* **Denial of Service:** Yes. Triggering the bug easily leads to a kernel panic/crash.
* **Accessible From Unprivileged Processes / User Namespaces:** No. The JFS filesystem does not have the `FS_USERNS_MOUNT` flag. Therefore, an unprivileged user cannot mount a crafted JFS image directly, not even within a user namespace. It requires `CAP_SYS_ADMIN` in the initial namespace.
* **Malicious Filesystem / Peripheral Trigger:** Yes. The bug can be triggered if the system is configured to auto-mount external media (e.g., plugging in a USB drive with a crafted JFS image on a Linux desktop environment running `udisks2`).
|
| 6/2 |
2026/05/26 00:08 |
llm |
expert |
0m
Model:
Tokens:
input: 15693
output: 37
thoughts: 654
Thoughts: **Analyzing a JFS Crash with syzkaller**
Okay, so I've got a syzkaller bug report here, and the crash is a GP fault. Looks like it's happening in `timestamp_truncate`, specifically called from `inode_set_ctime_current`. This is pretty classic, so let's break down the stack trace. I see the flow is `jfs_create` -> `path_openat` -> `do_sys_openat2` -> `__x64_sys_openat`, which gives us the user-space context.
The reproducer mounts a JFS image, then calls `openat`, which is interesting. Wait...it *specifically* calls `openat` on `cpuacct.usage_percpu` after changing the directory to the mounted image, so it's creating it? Hmmm, and the flags are `0x275a`. Okay, let me quickly decode that...let's see. Looks like `0x275a` decodes to `O_RDWR | O_CREAT | O_EXCL | O_TRUNC | O_APPEND | O_DIRECTORY`. That's a curious combination. Specifically, it's telling the kernel to create the file and then try to perform an operation using a combination of the O_APPEND, O_TRUNC and O_DIRECTORY flags.
So, the reproducer is attempting to *create* a file within the JFS filesystem with some rather odd open flags. I need to dig into `inode_set_ctime_current` and `timestamp_truncate` now. This looks like a potentially race condition or a specific edge case triggered during file creation and ctime update within JFS. Right, time to start tracing the code!
|
| 7/2 |
2026/05/26 00:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/inode.c IncludeLines:true Name:timestamp_truncate]
Results: map[SourceCode:2720: /**
2721: * timestamp_truncate - Truncate timespec to a granularity
2722: * @t: Timespec
2723: * @inode: inode being updated
2724: *
2725: * Truncate a timespec to the granularity supported by the fs
2726: * containing the inode. Always rounds down. gran must
2727: * not be 0 nor greater than a second (NSEC_PER_SEC, or 10^9 ns).
2728: */
2729: struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode)
2730: {
2731: struct super_block *sb = inode->i_sb;
2732: unsigned int gran = sb->s_time_gran;
2733:
2734: t.tv_sec = clamp(t.tv_sec, sb->s_time_min, sb->s_time_max);
2735: if (unlikely(t.tv_sec == sb->s_time_max || t.tv_sec == sb->s_time_min))
2736: t.tv_nsec = 0;
2737:
2738: /* Avoid division in the common cases 1 ns and 1 s. */
2739: if (gran == 1)
2740: ; /* nothing */
2741: else if (gran == NSEC_PER_SEC)
2742: t.tv_nsec = 0;
2743: else if (gran > 1 && gran < NSEC_PER_SEC)
2744: t.tv_nsec -= t.tv_nsec % gran;
2745: else
2746: WARN(1, "invalid file time granularity: %u", gran);
2747: return t;
2748: }
SourceFile:fs/inode.c]
|
| 8/2 |
2026/05/26 00:08 |
llm |
expert |
0m
Model:
Tokens:
input: 17291
output: 41
thoughts: 78
Thoughts: Okay, here's my take on those thoughts, framed as my own mental process:
**Debugging a Kernel Crash**
Alright, the crash is pinpointed at `fs/inode.c:2732`. That line: `unsigned int gran = sb->s_time_gran;` looks straightforward enough, but it's where things are falling apart. The crucial detail here is that `sb` is derived from `inode->i_sb`. My initial hunch? That `inode->i_sb` is a corrupted pointer – a wild pointer, to be precise. If it's pointing to some garbage memory, dereferencing it here is going to be a disaster.
So, the next logical step is to dive deeper into how `inode->i_sb` is being initialized and used. I need to trace back to where this `inode` structure is being set up. Let's start by scrutinizing the `inode_set_ctime_current` function. That's a likely point of interest, and I'll need to see how it interacts with the `inode` and its superblock. This is where the root cause probably lies, and I have to track it down.
|
| 9/2 |
2026/05/26 00:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/inode.c IncludeLines:true Name:inode_set_ctime_current]
Results: map[SourceCode:2751: /**
2752: * inode_set_ctime_current - set the ctime to current_time
2753: * @inode: inode
2754: *
2755: * Set the inode's ctime to the current value for the inode. Returns the
2756: * current value that was assigned. If this is not a multigrain inode, then we
2757: * set it to the later of the coarse time and floor value.
2758: *
2759: * If it is multigrain, then we first see if the coarse-grained timestamp is
2760: * distinct from what is already there. If so, then use that. Otherwise, get a
2761: * fine-grained timestamp.
2762: *
2763: * After that, try to swap the new value into i_ctime_nsec. Accept the
2764: * resulting ctime, regardless of the outcome of the swap. If it has
2765: * already been replaced, then that timestamp is later than the earlier
2766: * unacceptable one, and is thus acceptable.
2767: */
2768: struct timespec64 inode_set_ctime_current(struct inode *inode)
2769: {
2770: struct timespec64 now;
2771: u32 cns, cur;
2772:
2773: ktime_get_coarse_real_ts64_mg(&now);
2774: now = timestamp_truncate(now, inode);
2775:
2776: /* Just return that if this is not a multigrain fs */
2777: if (!is_mgtime(inode)) {
2778: inode_set_ctime_to_ts(inode, now);
2779: goto out;
2780: }
2781:
2782: /*
2783: * A fine-grained time is only needed if someone has queried
2784: * for timestamps, and the current coarse grained time isn't
2785: * later than what's already there.
2786: */
2787: cns = smp_load_acquire(&inode->i_ctime_nsec);
2788: if (cns & I_CTIME_QUERIED) {
2789: struct timespec64 ctime = { .tv_sec = inode->i_ctime_sec,
2790: .tv_nsec = cns & ~I_CTIME_QUERIED };
2791:
2792: if (timespec64_compare(&now, &ctime) <= 0) {
2793: ktime_get_real_ts64_mg(&now);
2794: now = timestamp_truncate(now, inode);
2795: mgtime_counter_inc(mg_fine_stamps);
2796: }
2797: }
2798: mgtime_counter_inc(mg_ctime_updates);
2799:
2800: /* No need to cmpxchg if it's exactly the same */
2801: if (cns == now.tv_nsec && inode->i_ctime_sec == now.tv_sec) {
2802: trace_ctime_xchg_skip(inode, &now);
2803: goto out;
2804: }
2805: cur = cns;
2806: retry:
2807: /* Try to swap the nsec value into place. */
2808: if (try_cmpxchg(&inode->i_ctime_nsec, &cur, now.tv_nsec)) {
2809: /* If swap occurred, then we're (mostly) done */
2810: inode->i_ctime_sec = now.tv_sec;
2811: trace_ctime_ns_xchg(inode, cns, now.tv_nsec, cur);
2812: mgtime_counter_inc(mg_ctime_swaps);
2813: } else {
2814: /*
2815: * Was the change due to someone marking the old ctime QUERIED?
2816: * If so then retry the swap. This can only happen once since
2817: * the only way to clear I_CTIME_QUERIED is to stamp the inode
2818: * with a new ctime.
2819: */
2820: if (!(cns & I_CTIME_QUERIED) && (cns | I_CTIME_QUERIED) == cur) {
2821: cns = cur;
2822: goto retry;
2823: }
2824: /* Otherwise, keep the existing ctime */
2825: now.tv_sec = inode->i_ctime_sec;
2826: now.tv_nsec = cur & ~I_CTIME_QUERIED;
2827: }
2828: out:
2829: return now;
2830: }
SourceFile:fs/inode.c]
|
| 10/2 |
2026/05/26 00:08 |
llm |
expert |
0m
Model:
Tokens:
input: 19035
output: 42
thoughts: 35
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of debugging a file system crash:
**Tracing a File System Crash in JFS**
Alright, I've got a crash, and the stack trace is pointing directly at `inode_set_ctime_current`. That's a pretty low-level function related to timestamps, usually accessed in a more general context. I know this function is part of the core timestamping and metadata management. So, I need to understand what's *triggering* it. The trace says it's being called from `jfs_create`. Okay, `jfs_create`. That's a good starting point. That function is responsible for creating *new* files and directories on the JFS file system. I need to dive into `jfs_create` and see what it's doing right before that call to `inode_set_ctime_current`. I want to identify any specific operations or data structures it's manipulating that could be the source of the problem. Time to dig in!
|
| 11/2 |
2026/05/26 00:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/namei.c IncludeLines:true Name:jfs_create]
Results: map[SourceCode: 48: /*
49: * NAME: jfs_create(dip, dentry, mode)
50: *
51: * FUNCTION: create a regular file in the parent directory <dip>
52: * with name = <from dentry> and mode = <mode>
53: *
54: * PARAMETER: dip - parent directory vnode
55: * dentry - dentry of new file
56: * mode - create mode (rwxrwxrwx).
57: * nd- nd struct
58: *
59: * RETURN: Errors from subroutines
60: *
61: */
62: static int jfs_create(struct mnt_idmap *idmap, struct inode *dip,
63: struct dentry *dentry, umode_t mode, bool excl)
64: {
65: int rc = 0;
66: tid_t tid; /* transaction id */
67: struct inode *ip = NULL; /* child directory inode */
68: ino_t ino;
69: struct component_name dname; /* child directory name */
70: struct btstack btstack;
71: struct inode *iplist[2];
72: struct tblock *tblk;
73:
74: jfs_info("jfs_create: dip:0x%p name:%pd", dip, dentry);
75:
76: rc = dquot_initialize(dip);
77: if (rc)
78: goto out1;
79:
80: /*
81: * search parent directory for entry/freespace
82: * (dtSearch() returns parent directory page pinned)
83: */
84: if ((rc = get_UCSname(&dname, dentry)))
85: goto out1;
86:
87: /*
88: * Either iAlloc() or txBegin() may block. Deadlock can occur if we
89: * block there while holding dtree page, so we allocate the inode &
90: * begin the transaction before we search the directory.
91: */
92: ip = ialloc(dip, mode);
93: if (IS_ERR(ip)) {
94: rc = PTR_ERR(ip);
95: goto out2;
96: }
97:
98: tid = txBegin(dip->i_sb, 0);
99:
100: mutex_lock_nested(&JFS_IP(dip)->commit_mutex, COMMIT_MUTEX_PARENT);
101: mutex_lock_nested(&JFS_IP(ip)->commit_mutex, COMMIT_MUTEX_CHILD);
102:
103: rc = jfs_init_acl(tid, ip, dip);
104: if (rc)
105: goto out3;
106:
107: rc = jfs_init_security(tid, ip, dip, &dentry->d_name);
108: if (rc) {
109: txAbort(tid, 0);
110: goto out3;
111: }
112:
113: if ((rc = dtSearch(dip, &dname, &ino, &btstack, JFS_CREATE))) {
114: jfs_err("jfs_create: dtSearch returned %d", rc);
115: txAbort(tid, 0);
116: goto out3;
117: }
118:
119: tblk = tid_to_tblock(tid);
120: tblk->xflag |= COMMIT_CREATE;
121: tblk->ino = ip->i_ino;
122: tblk->u.ixpxd = JFS_IP(ip)->ixpxd;
123:
124: iplist[0] = dip;
125: iplist[1] = ip;
126:
127: /*
128: * initialize the child XAD tree root in-line in inode
129: */
130: xtInitRoot(tid, ip);
131:
132: /*
133: * create entry in parent directory for child directory
134: * (dtInsert() releases parent directory page)
135: */
136: ino = ip->i_ino;
137: if ((rc = dtInsert(tid, dip, &dname, &ino, &btstack))) {
138: if (rc == -EIO) {
139: jfs_err("jfs_create: dtInsert returned -EIO");
140: txAbort(tid, 1); /* Marks Filesystem dirty */
141: } else
142: txAbort(tid, 0); /* Filesystem full */
143: goto out3;
144: }
145:
146: ip->i_op = &jfs_file_inode_operations;
147: ip->i_fop = &jfs_file_operations;
148: ip->i_mapping->a_ops = &jfs_aops;
149:
150: mark_inode_dirty(ip);
151:
152: inode_set_mtime_to_ts(dip, inode_set_ctime_current(dip));
153:
154: mark_inode_dirty(dip);
155:
156: rc = txCommit(tid, 2, &iplist[0], 0);
157:
158: out3:
159: txEnd(tid);
160: mutex_unlock(&JFS_IP(ip)->commit_mutex);
161: mutex_unlock(&JFS_IP(dip)->commit_mutex);
162: if (rc) {
163: free_ea_wmap(ip);
164: clear_nlink(ip);
165: discard_new_inode(ip);
166: } else {
167: d_instantiate_new(dentry, ip);
168: }
169:
170: out2:
171: free_UCSname(&dname);
172:
173: out1:
174:
175: jfs_info("jfs_create: rc:%d", rc);
176: return rc;
177: }
SourceFile:fs/jfs/namei.c]
|
| 12/2 |
2026/05/26 00:08 |
llm |
expert |
0m
Model:
Tokens:
input: 21216
output: 19
thoughts: 1080
Thoughts: **Debugging a Kernel Crash in `inode_set_ctime_current`**
Okay, so I've got a crash, and it's happening within `inode_set_ctime_current`. The backtrace points to the parent directory inode, `dip`. I need to figure out why this is hitting an issue accessing `sb->s_time_gran`, where `sb` is the super block of the inode. `dip` is definitely valid, because if it wasn't, the earlier `dtSearch` and `dtInsert` operations would have failed.
Let me look at the assembly around where it's crashing. Here it is:
```assembly
0: d8 48 c1 fmuls -0x3f(%rax)
3: e8 03 48 89 44 call 0x4489480b
8: 24 30 and $0x30,%al
a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1)
f: 74 08 je 0x19
11: 48 89 df mov %rbx,%rdi
14: e8 92 fc eb ff call 0xffebfcab
19: 4c 8b 3b mov (%rbx),%r15
1c: 49 8d bf a0 07 00 00 lea 0x7a0(%r15),%rdi
23: 48 89 f8 mov %rdi,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 0f b6 04 20 movzbl (%rax,%r12,1),%eax <-- trapping instruction
2f: 84 c0 test %al,%al
31: 0f 85 d6 07 00 00 jne 0x80d
37: 48 89 5c 24 20 mov %rbx,0x20(%rsp)
3c: 41 rex.B
3d: 8b .byte 0x8b
3e: 87 .byte 0x87
3f: a0 .byte 0xa0
```
Aha, that `movzbl` instruction at address `2a` is the culprit. And, given that it's trapping, this *has* to be KASAN (Kernel Address Sanitizer) at work! I can see `%r12` is the KASAN shadow offset, which is `dffffc0000000000`. So, that's not the actual data address. Let's look at what's in `%rax`.
`RAX: 000ea00e000c6102`.
Okay, that's the data address being checked. I'll need to figure out what's leading up to this. Let's see: `RDI: 0075007000630812`. `RDI` was computed by a `lea 0x7a0(%r15),%rdi`. So I should be able to figure out the address of the pointer from that.
`0075007000630812` - 0x7a0 = `%r15` which is `0075007000630072`.
`%r15` was loaded from `(%rbx)`. So, whatever `%rbx` points to is where `%r15` is calculated from. `%rbx` is `ffff8880526f3528`. Okay, `%rbx` is likely an `inode` pointer. Given this is where we're having the issue accessing the super block data, I need to check the offsets of the super block within the `inode` structure. From there, I can see how `sb->s_time_gran` is being calculated.
|
| 13/2 |
2026/05/26 00:09 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:i_mode OffsetBits:0 SizeBits:16] map[Name:i_opflags OffsetBits:16 SizeBits:16] map[Name:i_uid OffsetBits:32 SizeBits:32] map[Name:i_gid OffsetBits:64 SizeBits:32] map[Name:i_flags OffsetBits:96 SizeBits:32] map[Name:i_acl OffsetBits:128 SizeBits:64] map[Name:i_default_acl OffsetBits:192 SizeBits:64] map[Name:i_op OffsetBits:256 SizeBits:64] map[Name:i_sb OffsetBits:320 SizeBits:64] map[Name:i_mapping OffsetBits:384 SizeBits:64] map[Name:i_security OffsetBits:448 SizeBits:64] map[Name:i_ino OffsetBits:512 SizeBits:64] map[Name: OffsetBits:576 SizeBits:32] map[Name:i_rdev OffsetBits:608 SizeBits:32] map[Name:i_size OffsetBits:640 SizeBits:64] map[Name:i_atime_sec OffsetBits:704 SizeBits:64] map[Name:i_mtime_sec OffsetBits:768 SizeBits:64] map[Name:i_ctime_sec OffsetBits:832 SizeBits:64] map[Name:i_atime_nsec OffsetBits:896 SizeBits:32] map[Name:i_mtime_nsec OffsetBits:928 SizeBits:32] map[Name:i_ctime_nsec OffsetBits:960 SizeBits:32] map[Name:i_generation OffsetBits:992 SizeBits:32] map[Name:i_lock OffsetBits:1024 SizeBits:1024] map[Name:i_bytes OffsetBits:2048 SizeBits:16] map[Name:i_blkbits OffsetBits:2064 SizeBits:8] map[Name:i_write_hint OffsetBits:2072 SizeBits:8] map[Name:i_blocks OffsetBits:2112 SizeBits:64] map[Name:i_state OffsetBits:2176 SizeBits:32] map[Name:i_rwsem OffsetBits:2240 SizeBits:1088] map[Name:dirtied_when OffsetBits:3328 SizeBits:64] map[Name:dirtied_time_when OffsetBits:3392 SizeBits:64] map[Name:i_hash OffsetBits:3456 SizeBits:128] map[Name:i_io_list OffsetBits:3584 SizeBits:128] map[Name:i_wb OffsetBits:3712 SizeBits:64] map[Name:i_wb_frn_winner OffsetBits:3776 SizeBits:32] map[Name:i_wb_frn_avg_time OffsetBits:3808 SizeBits:16] map[Name:i_wb_frn_history OffsetBits:3824 SizeBits:16] map[Name:i_lru OffsetBits:3840 SizeBits:128] map[Name:i_sb_list OffsetBits:3968 SizeBits:128] map[Name:i_wb_list OffsetBits:4096 SizeBits:128] map[Name: OffsetBits:4224 SizeBits:128] map[Name:i_version OffsetBits:4352 SizeBits:64] map[Name:i_sequence OffsetBits:4416 SizeBits:64] map[Name:i_count OffsetBits:4480 SizeBits:32] map[Name:i_dio_count OffsetBits:4512 SizeBits:32] map[Name:i_writecount OffsetBits:4544 SizeBits:32] map[Name:i_readcount OffsetBits:4576 SizeBits:32] map[Name: OffsetBits:4608 SizeBits:64] map[Name:i_flctx OffsetBits:4672 SizeBits:64] map[Name:i_data OffsetBits:4736 SizeBits:5120] map[Name: OffsetBits:9856 SizeBits:128] map[Name: OffsetBits:9984 SizeBits:64] map[Name:i_fsnotify_mask OffsetBits:10048 SizeBits:32] map[Name:i_fsnotify_marks OffsetBits:10112 SizeBits:64] map[Name:i_private OffsetBits:10176 SizeBits:64]]]
|
| 14/2 |
2026/05/26 00:09 |
llm |
expert |
0m
Model:
Tokens:
input: 24597
output: 21
thoughts: 98
Thoughts: **Decoding the Assembly and Superblock Structure**
Okay, let me break this down. First, I see that `i_sb` is located at an offset of 320 bits, which is equivalent to 40 bytes or 0x28 in hexadecimal. That makes sense, but the assembly code then throws a curveball. The critical instructions here are `mov (%rbx),%r15` followed by `lea 0x7a0(%r15),%rdi`. I'm guessing `%rbx` is a pointer related to the superblock structure, the first instruction moves the value pointed to by `%rbx` into the `%r15` register. The second instruction uses that value in `%r15` and calculates the address `0x7a0` bytes beyond what's in `%r15` into the `%rdi` register. The key thing I need to figure out is what that offset, `0x7a0` (which is 1952 in decimal), signifies within the context of a `struct super_block`. It's clear that the address calculation is offset relative to some data found at offset zero in the structure pointed to by `%rbx`. Now, I just need to remember or quickly look up the structure definition to find out what field is at offset 1952. Knowing the filesystem type would help focus the search and make this trivial.
|
| 15/2 |
2026/05/26 00:09 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:s_list OffsetBits:0 SizeBits:128] map[Name:s_dev OffsetBits:128 SizeBits:32] map[Name:s_blocksize_bits OffsetBits:160 SizeBits:8] map[Name:s_blocksize OffsetBits:192 SizeBits:64] map[Name:s_maxbytes OffsetBits:256 SizeBits:64] map[Name:s_type OffsetBits:320 SizeBits:64] map[Name:s_op OffsetBits:384 SizeBits:64] map[Name:dq_op OffsetBits:448 SizeBits:64] map[Name:s_qcop OffsetBits:512 SizeBits:64] map[Name:s_export_op OffsetBits:576 SizeBits:64] map[Name:s_flags OffsetBits:640 SizeBits:64] map[Name:s_iflags OffsetBits:704 SizeBits:64] map[Name:s_magic OffsetBits:768 SizeBits:64] map[Name:s_root OffsetBits:832 SizeBits:64] map[Name:s_umount OffsetBits:896 SizeBits:1088] map[Name:s_count OffsetBits:1984 SizeBits:32] map[Name:s_active OffsetBits:2016 SizeBits:32] map[Name:s_security OffsetBits:2048 SizeBits:64] map[Name:s_xattr OffsetBits:2112 SizeBits:64] map[Name:s_cop OffsetBits:2176 SizeBits:64] map[Name:s_master_keys OffsetBits:2240 SizeBits:64] map[Name:s_vop OffsetBits:2304 SizeBits:64] map[Name:s_encoding OffsetBits:2368 SizeBits:64] map[Name:s_encoding_flags OffsetBits:2432 SizeBits:16] map[Name:s_roots OffsetBits:2496 SizeBits:64] map[Name:s_mounts OffsetBits:2560 SizeBits:64] map[Name:s_bdev OffsetBits:2624 SizeBits:64] map[Name:s_bdev_file OffsetBits:2688 SizeBits:64] map[Name:s_bdi OffsetBits:2752 SizeBits:64] map[Name:s_mtd OffsetBits:2816 SizeBits:64] map[Name:s_instances OffsetBits:2880 SizeBits:128] map[Name:s_quota_types OffsetBits:3008 SizeBits:32] map[Name:s_dquot OffsetBits:3072 SizeBits:3264] map[Name:s_writers OffsetBits:6336 SizeBits:9216] map[Name:s_fs_info OffsetBits:15552 SizeBits:64] map[Name:s_time_gran OffsetBits:15616 SizeBits:32] map[Name:s_time_min OffsetBits:15680 SizeBits:64] map[Name:s_time_max OffsetBits:15744 SizeBits:64] map[Name:s_fsnotify_mask OffsetBits:15808 SizeBits:32] map[Name:s_fsnotify_info OffsetBits:15872 SizeBits:64] map[Name:s_id OffsetBits:15936 SizeBits:256] map[Name:s_uuid OffsetBits:16192 SizeBits:128] map[Name:s_uuid_len OffsetBits:16320 SizeBits:8] map[Name:s_sysfs_name OffsetBits:16328 SizeBits:296] map[Name:s_max_links OffsetBits:16640 SizeBits:32] map[Name:s_d_flags OffsetBits:16672 SizeBits:32] map[Name:s_vfs_rename_mutex OffsetBits:16704 SizeBits:1024] map[Name:s_subtype OffsetBits:17728 SizeBits:64] map[Name:__s_d_op OffsetBits:17792 SizeBits:64] map[Name:s_shrink OffsetBits:17856 SizeBits:64] map[Name:s_remove_count OffsetBits:17920 SizeBits:64] map[Name:s_readonly_remount OffsetBits:17984 SizeBits:32] map[Name:s_wb_err OffsetBits:18016 SizeBits:32] map[Name:s_dio_done_wq OffsetBits:18048 SizeBits:64] map[Name:s_pins OffsetBits:18112 SizeBits:64] map[Name:s_user_ns OffsetBits:18176 SizeBits:64] map[Name:s_dentry_lru OffsetBits:18240 SizeBits:1472] map[Name:s_inode_lru OffsetBits:19712 SizeBits:1472] map[Name:rcu OffsetBits:21184 SizeBits:128] map[Name:destroy_work OffsetBits:21312 SizeBits:576] map[Name:s_sync_lock OffsetBits:21888 SizeBits:1024] map[Name:s_stack_depth OffsetBits:22912 SizeBits:32] map[Name:s_inode_list_lock OffsetBits:23040 SizeBits:1024] map[Name:s_inodes OffsetBits:24064 SizeBits:128] map[Name:s_inode_wblist_lock OffsetBits:24192 SizeBits:1024] map[Name:s_inodes_wb OffsetBits:25216 SizeBits:128]]]
|
| 16/2 |
2026/05/26 00:09 |
llm |
expert |
0m
Model:
Tokens:
input: 26616
output: 41
thoughts: 664
Thoughts: **Deconstructing the Register's Role**
Okay, so I'm digging into this code, trying to understand how `s_time_gran` is being accessed. I see it's at offset 15616 bits, which is 1952 bytes, or 0x7a0. This means `r15` is holding the value of `sb`, that's the super block. Then I trace back and find that `r15` was loaded from `(%rbx)`. That's where it gets interesting...
Why is it loading from `(%rbx)`? I know that `i_sb` within the `struct inode` is at offset 0x28 (40 bytes). Initially, I thought that `rbx` *might* be `inode` itself, which would be odd.
Let me double-check the disassembly quickly... Hmm, there's a `mov %rbx, %rdi`, followed by a `call` to `0xffebfcab`. Hold on... what's that call doing? It looks like it *could* be `inode_set_ctime_current`. But wait, that function is inlined... I need to look at the RIP, it's `inode_set_ctime_current+0xcf/0xb40`. Got it, that's not inlined.
Let's quickly review the `inode_set_ctime_current` code. I remember it calls `ktime_get_coarse_real_ts64_mg` and then `timestamp_truncate`. Now, `ktime_get_coarse_real_ts64_mg` takes a `&now` as an argument, and `now` is a local variable. So... the `rbx` argument is likely something else. And if `rbx` was `inode`, then `mov (%rbx),%r15` would be loading something like `i_mode` and `i_opflags` at offset 0x0.
Okay, let me review the `struct inode` layout one more time... Wait a minute, what if `rbx` isn't `inode` itself, but something *related*? The address in `RBX` is what matters...
Let's look at the registers again... Ah-ha! `RBX: ffff8880526f3528`. Look at that, `0x28` is at the end of the address! So, `RBX` is actually `inode + 0x28`! That's it!
So, the code is using `rbx` as a pointer to `&inode->i_sb`!
Why? Well, `inode_set_ctime_current` might have done a `lea 0x28(%rdi), %rbx` to get `&inode->i_sb`. But, no, `RBX` is callee-saved, so it might have been set up earlier. I should really check the source of `inode_set_ctime_current` to be sure.
|
| 17/2 |
2026/05/26 00:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/inode.c IncludeLines:true Name:inode_set_ctime_current]
Results: map[SourceCode:2751: /**
2752: * inode_set_ctime_current - set the ctime to current_time
2753: * @inode: inode
2754: *
2755: * Set the inode's ctime to the current value for the inode. Returns the
2756: * current value that was assigned. If this is not a multigrain inode, then we
2757: * set it to the later of the coarse time and floor value.
2758: *
2759: * If it is multigrain, then we first see if the coarse-grained timestamp is
2760: * distinct from what is already there. If so, then use that. Otherwise, get a
2761: * fine-grained timestamp.
2762: *
2763: * After that, try to swap the new value into i_ctime_nsec. Accept the
2764: * resulting ctime, regardless of the outcome of the swap. If it has
2765: * already been replaced, then that timestamp is later than the earlier
2766: * unacceptable one, and is thus acceptable.
2767: */
2768: struct timespec64 inode_set_ctime_current(struct inode *inode)
2769: {
2770: struct timespec64 now;
2771: u32 cns, cur;
2772:
2773: ktime_get_coarse_real_ts64_mg(&now);
2774: now = timestamp_truncate(now, inode);
2775:
2776: /* Just return that if this is not a multigrain fs */
2777: if (!is_mgtime(inode)) {
2778: inode_set_ctime_to_ts(inode, now);
2779: goto out;
2780: }
2781:
2782: /*
2783: * A fine-grained time is only needed if someone has queried
2784: * for timestamps, and the current coarse grained time isn't
2785: * later than what's already there.
2786: */
2787: cns = smp_load_acquire(&inode->i_ctime_nsec);
2788: if (cns & I_CTIME_QUERIED) {
2789: struct timespec64 ctime = { .tv_sec = inode->i_ctime_sec,
2790: .tv_nsec = cns & ~I_CTIME_QUERIED };
2791:
2792: if (timespec64_compare(&now, &ctime) <= 0) {
2793: ktime_get_real_ts64_mg(&now);
2794: now = timestamp_truncate(now, inode);
2795: mgtime_counter_inc(mg_fine_stamps);
2796: }
2797: }
2798: mgtime_counter_inc(mg_ctime_updates);
2799:
2800: /* No need to cmpxchg if it's exactly the same */
2801: if (cns == now.tv_nsec && inode->i_ctime_sec == now.tv_sec) {
2802: trace_ctime_xchg_skip(inode, &now);
2803: goto out;
2804: }
2805: cur = cns;
2806: retry:
2807: /* Try to swap the nsec value into place. */
2808: if (try_cmpxchg(&inode->i_ctime_nsec, &cur, now.tv_nsec)) {
2809: /* If swap occurred, then we're (mostly) done */
2810: inode->i_ctime_sec = now.tv_sec;
2811: trace_ctime_ns_xchg(inode, cns, now.tv_nsec, cur);
2812: mgtime_counter_inc(mg_ctime_swaps);
2813: } else {
2814: /*
2815: * Was the change due to someone marking the old ctime QUERIED?
2816: * If so then retry the swap. This can only happen once since
2817: * the only way to clear I_CTIME_QUERIED is to stamp the inode
2818: * with a new ctime.
2819: */
2820: if (!(cns & I_CTIME_QUERIED) && (cns | I_CTIME_QUERIED) == cur) {
2821: cns = cur;
2822: goto retry;
2823: }
2824: /* Otherwise, keep the existing ctime */
2825: now.tv_sec = inode->i_ctime_sec;
2826: now.tv_nsec = cur & ~I_CTIME_QUERIED;
2827: }
2828: out:
2829: return now;
2830: }
SourceFile:fs/inode.c]
|
| 18/2 |
2026/05/26 00:09 |
llm |
expert |
0m
Model:
Tokens:
input: 29370
output: 42
thoughts: 1282
Thoughts: **Debugging a Kernel Crash in `timestamp_truncate`**
Okay, so I'm looking at this kernel crash, and my initial thought is that `timestamp_truncate` is being called twice. Seems like a simple thing, right? But the stack trace points to the *first* call, and I need to figure out why.
The debugger's showing me the assembly code, and I'm trying to follow the execution. `rbx` seems to be passed as the first argument, and initially, I thought it was `&now`, but then `ktime_get_coarse_real_ts64_mg` takes that as an argument, so I was wrong. The code then loads something from the address in `rbx`. I thought I was getting somewhere, maybe it was `&inode->i_sb`, but the disassembly for the second instruction has got me thrown.
I was focusing on the wrong call. I'm now certain that the call I thought was `ktime_get_coarse_real_ts64_mg` is actually `__asan_report_load8`. Aha! That explains the crash, now I'm getting somewhere. So `__asan_report_load8` is complaining about an 8-byte load from `rbx`, which is `&inode->i_sb`!
So, `inode->i_sb` holds garbage. It's a wild pointer! That's the root cause. This confirms the report. But why?
I'll have to investigate how `inode->i_sb` gets set, likely starting with the `jfs_create` function.
|
| 19/2 |
2026/05/26 00:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/namei.c IncludeLines:true Name:jfs_create]
Results: map[SourceCode: 48: /*
49: * NAME: jfs_create(dip, dentry, mode)
50: *
51: * FUNCTION: create a regular file in the parent directory <dip>
52: * with name = <from dentry> and mode = <mode>
53: *
54: * PARAMETER: dip - parent directory vnode
55: * dentry - dentry of new file
56: * mode - create mode (rwxrwxrwx).
57: * nd- nd struct
58: *
59: * RETURN: Errors from subroutines
60: *
61: */
62: static int jfs_create(struct mnt_idmap *idmap, struct inode *dip,
63: struct dentry *dentry, umode_t mode, bool excl)
64: {
65: int rc = 0;
66: tid_t tid; /* transaction id */
67: struct inode *ip = NULL; /* child directory inode */
68: ino_t ino;
69: struct component_name dname; /* child directory name */
70: struct btstack btstack;
71: struct inode *iplist[2];
72: struct tblock *tblk;
73:
74: jfs_info("jfs_create: dip:0x%p name:%pd", dip, dentry);
75:
76: rc = dquot_initialize(dip);
77: if (rc)
78: goto out1;
79:
80: /*
81: * search parent directory for entry/freespace
82: * (dtSearch() returns parent directory page pinned)
83: */
84: if ((rc = get_UCSname(&dname, dentry)))
85: goto out1;
86:
87: /*
88: * Either iAlloc() or txBegin() may block. Deadlock can occur if we
89: * block there while holding dtree page, so we allocate the inode &
90: * begin the transaction before we search the directory.
91: */
92: ip = ialloc(dip, mode);
93: if (IS_ERR(ip)) {
94: rc = PTR_ERR(ip);
95: goto out2;
96: }
97:
98: tid = txBegin(dip->i_sb, 0);
99:
100: mutex_lock_nested(&JFS_IP(dip)->commit_mutex, COMMIT_MUTEX_PARENT);
101: mutex_lock_nested(&JFS_IP(ip)->commit_mutex, COMMIT_MUTEX_CHILD);
102:
103: rc = jfs_init_acl(tid, ip, dip);
104: if (rc)
105: goto out3;
106:
107: rc = jfs_init_security(tid, ip, dip, &dentry->d_name);
108: if (rc) {
109: txAbort(tid, 0);
110: goto out3;
111: }
112:
113: if ((rc = dtSearch(dip, &dname, &ino, &btstack, JFS_CREATE))) {
114: jfs_err("jfs_create: dtSearch returned %d", rc);
115: txAbort(tid, 0);
116: goto out3;
117: }
118:
119: tblk = tid_to_tblock(tid);
120: tblk->xflag |= COMMIT_CREATE;
121: tblk->ino = ip->i_ino;
122: tblk->u.ixpxd = JFS_IP(ip)->ixpxd;
123:
124: iplist[0] = dip;
125: iplist[1] = ip;
126:
127: /*
128: * initialize the child XAD tree root in-line in inode
129: */
130: xtInitRoot(tid, ip);
131:
132: /*
133: * create entry in parent directory for child directory
134: * (dtInsert() releases parent directory page)
135: */
136: ino = ip->i_ino;
137: if ((rc = dtInsert(tid, dip, &dname, &ino, &btstack))) {
138: if (rc == -EIO) {
139: jfs_err("jfs_create: dtInsert returned -EIO");
140: txAbort(tid, 1); /* Marks Filesystem dirty */
141: } else
142: txAbort(tid, 0); /* Filesystem full */
143: goto out3;
144: }
145:
146: ip->i_op = &jfs_file_inode_operations;
147: ip->i_fop = &jfs_file_operations;
148: ip->i_mapping->a_ops = &jfs_aops;
149:
150: mark_inode_dirty(ip);
151:
152: inode_set_mtime_to_ts(dip, inode_set_ctime_current(dip));
153:
154: mark_inode_dirty(dip);
155:
156: rc = txCommit(tid, 2, &iplist[0], 0);
157:
158: out3:
159: txEnd(tid);
160: mutex_unlock(&JFS_IP(ip)->commit_mutex);
161: mutex_unlock(&JFS_IP(dip)->commit_mutex);
162: if (rc) {
163: free_ea_wmap(ip);
164: clear_nlink(ip);
165: discard_new_inode(ip);
166: } else {
167: d_instantiate_new(dentry, ip);
168: }
169:
170: out2:
171: free_UCSname(&dname);
172:
173: out1:
174:
175: jfs_info("jfs_create: rc:%d", rc);
176: return rc;
177: }
SourceFile:fs/jfs/namei.c]
|
| 20/2 |
2026/05/26 00:09 |
llm |
expert |
0m
Model:
Tokens:
input: 32921
output: 44
thoughts: 98
Thoughts: **Analyzing a Potential Memory Issue**
Okay, hold on a second! I'm looking at this line of code: `inode_set_mtime_to_ts(dip, inode_set_ctime_current(dip));`. The key here is `dip`. Is `dip` the inode of the *parent* directory? I'm pretty sure it is.
But wait a minute... I remember seeing `dip` passed to `txBegin(dip->i_sb, 0)`. That's interesting, because if `dip->i_sb` were some kind of wild, corrupt pointer, `txBegin` would have *definitely* crashed, right? The system would have gone down, hard. That seems like an unlikely outcome, given the context.
Let's just take a moment and confirm that behavior by checking the implementation of `txBegin`. I want to make *absolutely* sure we can trust the current code path. Better safe than sorry.
|
| 21/2 |
2026/05/26 00:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_txnmgr.c IncludeLines:true Name:txBegin]
Results: map[SourceCode: 336: /*
337: * NAME: txBegin()
338: *
339: * FUNCTION: start a transaction.
340: *
341: * PARAMETER: sb - superblock
342: * flag - force for nested tx;
343: *
344: * RETURN: tid - transaction id
345: *
346: * note: flag force allows to start tx for nested tx
347: * to prevent deadlock on logsync barrier;
348: */
349: tid_t txBegin(struct super_block *sb, int flag)
350: {
351: tid_t t;
352: struct tblock *tblk;
353: struct jfs_log *log;
354:
355: jfs_info("txBegin: flag = 0x%x", flag);
356: log = JFS_SBI(sb)->log;
357:
358: if (!log) {
359: jfs_error(sb, "read-only filesystem\n");
360: return 0;
361: }
362:
363: TXN_LOCK();
364:
365: INCREMENT(TxStat.txBegin);
366:
367: retry:
368: if (!(flag & COMMIT_FORCE)) {
369: /*
370: * synchronize with logsync barrier
371: */
372: if (test_bit(log_SYNCBARRIER, &log->flag) ||
373: test_bit(log_QUIESCE, &log->flag)) {
374: INCREMENT(TxStat.txBegin_barrier);
375: TXN_SLEEP(&log->syncwait);
376: goto retry;
377: }
378: }
379: if (flag == 0) {
380: /*
381: * Don't begin transaction if we're getting starved for tlocks
382: * unless COMMIT_FORCE or COMMIT_INODE (which may ultimately
383: * free tlocks)
384: */
385: if (TxAnchor.tlocksInUse > TxLockVHWM) {
386: INCREMENT(TxStat.txBegin_lockslow);
387: TXN_SLEEP(&TxAnchor.lowlockwait);
388: goto retry;
389: }
390: }
391:
392: /*
393: * allocate transaction id/block
394: */
395: if ((t = TxAnchor.freetid) == 0) {
396: jfs_info("txBegin: waiting for free tid");
397: INCREMENT(TxStat.txBegin_freetid);
398: TXN_SLEEP(&TxAnchor.freewait);
399: goto retry;
400: }
401:
402: tblk = tid_to_tblock(t);
403:
404: if ((tblk->next == 0) && !(flag & COMMIT_FORCE)) {
405: /* Don't let a non-forced transaction take the last tblk */
406: jfs_info("txBegin: waiting for free tid");
407: INCREMENT(TxStat.txBegin_freetid);
408: TXN_SLEEP(&TxAnchor.freewait);
409: goto retry;
410: }
411:
412: TxAnchor.freetid = tblk->next;
413:
414: /*
415: * initialize transaction
416: */
417:
418: /*
419: * We can't zero the whole thing or we screw up another thread being
420: * awakened after sleeping on tblk->waitor
421: *
422: * memset(tblk, 0, sizeof(struct tblock));
423: */
424: tblk->next = tblk->last = tblk->xflag = tblk->flag = tblk->lsn = 0;
425:
426: tblk->sb = sb;
427: ++log->logtid;
428: tblk->logtid = log->logtid;
429:
430: ++log->active;
431:
432: HIGHWATERMARK(stattx.maxtid, t); /* statistics */
433: INCREMENT(stattx.ntid); /* statistics */
434:
435: TXN_UNLOCK();
436:
437: jfs_info("txBegin: returning tid = %d", t);
438:
439: return t;
440: }
SourceFile:fs/jfs/jfs_txnmgr.c]
|
| 22/2 |
2026/05/26 00:09 |
llm |
expert |
0m
Model:
Tokens:
input: 34714
output: 43
thoughts: 241
Thoughts: **Debugging a Subtle JFS Crash**
Okay, let's think this through. `txBegin` touches `sb` and `JFS_SBI(sb)->log`. If `sb` were garbage, we'd have a crash immediately in `txBegin`, right? But `txBegin` didn't crash, so `dip->i_sb` *was* valid when `txBegin` was called. That eliminates the obvious "wild pointer" in the superblock. But then we crashed later in `inode_set_ctime_current(dip)`.
Wait, going back to `jfs_create`, I see:
```c
inode_set_mtime_to_ts(dip, inode_set_ctime_current(dip));
```
The problem is now starting to focus on `dip`, the parent directory inode. Could `dip` have been freed or corrupted *between* the successful `txBegin` and the later `inode_set_ctime_current` call?
Crucially, `dip` is locked with a commit mutex right at the beginning of the call to jfs_create. specifically by `mutex_lock_nested(&JFS_IP(dip)->commit_mutex, COMMIT_MUTEX_PARENT);`, so that makes it much less likely. This means that if it *was* freed and reused, the lock should have prevented it.
The interesting thing is that `inode_set_ctime_current(dip)` is called *after* the `dtInsert` call: `dtInsert(tid, dip, &dname, &ino, &btstack)`. Could `dtInsert` have somehow corrupted `dip`? It's a plausible cause. It's time to dive into `dtInsert` and see if something there is mangling the directory inode's data.
|
| 23/2 |
2026/05/26 00:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dtree.c IncludeLines:true Name:dtInsert]
Results: map[SourceCode: 805: /*
806: * dtInsert()
807: *
808: * function: insert an entry to directory tree
809: *
810: * parameter:
811: *
812: * return: 0 - success;
813: * errno - failure;
814: */
815: int dtInsert(tid_t tid, struct inode *ip,
816: struct component_name * name, ino_t * fsn, struct btstack * btstack)
817: {
818: int rc = 0;
819: struct metapage *mp; /* meta-page buffer */
820: dtpage_t *p; /* base B+-tree index page */
821: s64 bn;
822: int index;
823: struct dtsplit split; /* split information */
824: ddata_t data;
825: struct dt_lock *dtlck;
826: int n;
827: struct tlock *tlck;
828: struct lv *lv;
829:
830: /*
831: * retrieve search result
832: *
833: * dtSearch() returns (leaf page pinned, index at which to insert).
834: * n.b. dtSearch() may return index of (maxindex + 1) of
835: * the full page.
836: */
837: DT_GETSEARCH(ip, btstack->top, bn, mp, p, index);
838: if (p->header.freelist == 0)
839: return -EINVAL;
840:
841: /*
842: * insert entry for new key
843: */
844: if (DO_INDEX(ip)) {
845: if (JFS_IP(ip)->next_index == DIREND) {
846: DT_PUTPAGE(mp);
847: return -EMLINK;
848: }
849: n = NDTLEAF(name->namlen);
850: data.leaf.tid = tid;
851: data.leaf.ip = ip;
852: } else {
853: n = NDTLEAF_LEGACY(name->namlen);
854: data.leaf.ip = NULL; /* signifies legacy directory format */
855: }
856: data.leaf.ino = *fsn;
857:
858: /*
859: * leaf page does not have enough room for new entry:
860: *
861: * extend/split the leaf page;
862: *
863: * dtSplitUp() will insert the entry and unpin the leaf page.
864: */
865: if (n > p->header.freecnt) {
866: split.mp = mp;
867: split.index = index;
868: split.nslot = n;
869: split.key = name;
870: split.data = &data;
871: rc = dtSplitUp(tid, ip, &split, btstack);
872: return rc;
873: }
874:
875: /*
876: * leaf page does have enough room for new entry:
877: *
878: * insert the new data entry into the leaf page;
879: */
880: BT_MARK_DIRTY(mp, ip);
881: /*
882: * acquire a transaction lock on the leaf page
883: */
884: tlck = txLock(tid, ip, mp, tlckDTREE | tlckENTRY);
885: dtlck = (struct dt_lock *) & tlck->lock;
886: ASSERT(dtlck->index == 0);
887: lv = & dtlck->lv[0];
888:
889: /* linelock header */
890: lv->offset = 0;
891: lv->length = 1;
892: dtlck->index++;
893:
894: dtInsertEntry(p, index, name, &data, &dtlck);
895:
896: /* linelock stbl of non-root leaf page */
897: if (!(p->header.flag & BT_ROOT)) {
898: if (dtlck->index >= dtlck->maxcnt)
899: dtlck = (struct dt_lock *) txLinelock(dtlck);
900: lv = & dtlck->lv[dtlck->index];
901: n = index >> L2DTSLOTSIZE;
902: lv->offset = p->header.stblindex + n;
903: lv->length =
904: ((p->header.nextindex - 1) >> L2DTSLOTSIZE) - n + 1;
905: dtlck->index++;
906: }
907:
908: /* unpin the leaf page */
909: DT_PUTPAGE(mp);
910:
911: return 0;
912: }
SourceFile:fs/jfs/jfs_dtree.c]
|
| 24/2 |
2026/05/26 00:09 |
llm |
expert |
0m
Model:
Tokens:
input: 36954
output: 42
thoughts: 1192
Thoughts: **Analyzing a Kernel Crash: The JFS File System Conundrum**
Okay, let's break this down. First, I'm thinking, `dtInsert` seems to be the culprit. It calls either `dtSplitUp` or `dtInsertEntry` – that's the starting point. I need to be sure the `dip` isn't freed prematurely, but the VFS should pin it. But, wait, what if `dip` isn't the inode of the parent directory? In `jfs_create`, `dip` *is* the parent directory's inode. I should go back and re-examine the crash.
Okay, let's look at the assembly. `mov (%rbx),%r15`, then `lea 0x7a0(%r15),%rdi`, and `movzbl (%rax,%r12,1),%eax`. Alright, the crash dump tells me that `%rax` holds `000ea00e000c6102`, and `%r15` has `0075007000630072`. Now, `%rdi` ends up as `0075007000630812`.
Hang on, `%rax` is `000ea00e000c6102`. But, `%rax` is supposed to be derived from `%rdi >> 3`. Checking, `0075007000630812 >> 3` *does* equal `000ea00e000c6102`. Yes! KASAN is confirming a check at address `0075007000630812`. But, where does `0075007000630072` come from? It comes from `(%rbx)`.
Okay, `%rbx` is `ffff8880526f3528`. That's a valid kernel address in the direct mapping, so let's check what's there. If `rbx` is `&inode->i_sb`, then `inode` is `ffff8880526f3500`. Let's see if that's a valid inode. And if it is, why does `i_sb` contain `0075007000630072`? Could this be a use-after-free situation with the inode? Or maybe a buffer overflow has corrupted the inode?
Wait a minute, `ffff8880526f3500` is the `inode`. Now, what is `0075007000630072`? Let's check it in ASCII... We get `r \0 c \0 p \0 u \0`. "r.c.p.u."? "rcpu"?
Wait! The reproducer opens `cpuacct.usage_percpu`. Oh! C is 0x63, P is 0x70, U is 0x75, A is 0x61, C is 0x63, C is 0x63, T is 0x74. So, `0075007000630072` is: `72 00 63 00 70 00 75 00` which means "rcpu" in UTF-16LE.
The `inode->i_sb` was overwritten with a UTF-16LE string! This appears to come from the filename. Now I need to figure out *how* a filename can overwrite `inode->i_sb`. Let's re-examine `jfs_create`.
|
| 25/2 |
2026/05/26 00:10 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/namei.c IncludeLines:true Name:jfs_create]
Results: map[SourceCode: 48: /*
49: * NAME: jfs_create(dip, dentry, mode)
50: *
51: * FUNCTION: create a regular file in the parent directory <dip>
52: * with name = <from dentry> and mode = <mode>
53: *
54: * PARAMETER: dip - parent directory vnode
55: * dentry - dentry of new file
56: * mode - create mode (rwxrwxrwx).
57: * nd- nd struct
58: *
59: * RETURN: Errors from subroutines
60: *
61: */
62: static int jfs_create(struct mnt_idmap *idmap, struct inode *dip,
63: struct dentry *dentry, umode_t mode, bool excl)
64: {
65: int rc = 0;
66: tid_t tid; /* transaction id */
67: struct inode *ip = NULL; /* child directory inode */
68: ino_t ino;
69: struct component_name dname; /* child directory name */
70: struct btstack btstack;
71: struct inode *iplist[2];
72: struct tblock *tblk;
73:
74: jfs_info("jfs_create: dip:0x%p name:%pd", dip, dentry);
75:
76: rc = dquot_initialize(dip);
77: if (rc)
78: goto out1;
79:
80: /*
81: * search parent directory for entry/freespace
82: * (dtSearch() returns parent directory page pinned)
83: */
84: if ((rc = get_UCSname(&dname, dentry)))
85: goto out1;
86:
87: /*
88: * Either iAlloc() or txBegin() may block. Deadlock can occur if we
89: * block there while holding dtree page, so we allocate the inode &
90: * begin the transaction before we search the directory.
91: */
92: ip = ialloc(dip, mode);
93: if (IS_ERR(ip)) {
94: rc = PTR_ERR(ip);
95: goto out2;
96: }
97:
98: tid = txBegin(dip->i_sb, 0);
99:
100: mutex_lock_nested(&JFS_IP(dip)->commit_mutex, COMMIT_MUTEX_PARENT);
101: mutex_lock_nested(&JFS_IP(ip)->commit_mutex, COMMIT_MUTEX_CHILD);
102:
103: rc = jfs_init_acl(tid, ip, dip);
104: if (rc)
105: goto out3;
106:
107: rc = jfs_init_security(tid, ip, dip, &dentry->d_name);
108: if (rc) {
109: txAbort(tid, 0);
110: goto out3;
111: }
112:
113: if ((rc = dtSearch(dip, &dname, &ino, &btstack, JFS_CREATE))) {
114: jfs_err("jfs_create: dtSearch returned %d", rc);
115: txAbort(tid, 0);
116: goto out3;
117: }
118:
119: tblk = tid_to_tblock(tid);
120: tblk->xflag |= COMMIT_CREATE;
121: tblk->ino = ip->i_ino;
122: tblk->u.ixpxd = JFS_IP(ip)->ixpxd;
123:
124: iplist[0] = dip;
125: iplist[1] = ip;
126:
127: /*
128: * initialize the child XAD tree root in-line in inode
129: */
130: xtInitRoot(tid, ip);
131:
132: /*
133: * create entry in parent directory for child directory
134: * (dtInsert() releases parent directory page)
135: */
136: ino = ip->i_ino;
137: if ((rc = dtInsert(tid, dip, &dname, &ino, &btstack))) {
138: if (rc == -EIO) {
139: jfs_err("jfs_create: dtInsert returned -EIO");
140: txAbort(tid, 1); /* Marks Filesystem dirty */
141: } else
142: txAbort(tid, 0); /* Filesystem full */
143: goto out3;
144: }
145:
146: ip->i_op = &jfs_file_inode_operations;
147: ip->i_fop = &jfs_file_operations;
148: ip->i_mapping->a_ops = &jfs_aops;
149:
150: mark_inode_dirty(ip);
151:
152: inode_set_mtime_to_ts(dip, inode_set_ctime_current(dip));
153:
154: mark_inode_dirty(dip);
155:
156: rc = txCommit(tid, 2, &iplist[0], 0);
157:
158: out3:
159: txEnd(tid);
160: mutex_unlock(&JFS_IP(ip)->commit_mutex);
161: mutex_unlock(&JFS_IP(dip)->commit_mutex);
162: if (rc) {
163: free_ea_wmap(ip);
164: clear_nlink(ip);
165: discard_new_inode(ip);
166: } else {
167: d_instantiate_new(dentry, ip);
168: }
169:
170: out2:
171: free_UCSname(&dname);
172:
173: out1:
174:
175: jfs_info("jfs_create: rc:%d", rc);
176: return rc;
177: }
SourceFile:fs/jfs/namei.c]
|
| 26/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 40920
output: 24
thoughts: 87
Thoughts: Okay, let me think this through.
**Analyzing the `dtInsert` Function and Its Interaction with Inline Directories in JFS**
Right, so `dtInsert` – that's the function that's supposed to be inserting this new file name. It's putting the name into the parent directory, but I need to make sure I understand *how*. If `dip` represents an inline directory, then `dtInsert` isn't writing to a traditional directory block. It's likely writing the file name and inode number directly into `dip->i_data` or a similar field within the inode itself.
Hold on, `dip`... that's an inode, isn't it? Okay, good. That clarifies things. Now I need to remember how JFS handles inline data. In JFS, the key struct is `jfs_inode_info`. That's where the inline data for inodes is stored. Okay, so I should take a look at `struct jfs_inode_info` structure again to make sure that my assumptions regarding how `dtInsert` writes inline directory data are correct.
|
| 27/2 |
2026/05/26 00:10 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:fileset OffsetBits:0 SizeBits:32] map[Name:mode2 OffsetBits:32 SizeBits:32] map[Name:saved_uid OffsetBits:64 SizeBits:32] map[Name:saved_gid OffsetBits:96 SizeBits:32] map[Name:ixpxd OffsetBits:128 SizeBits:64] map[Name:acl OffsetBits:192 SizeBits:128] map[Name:ea OffsetBits:320 SizeBits:128] map[Name:otime OffsetBits:448 SizeBits:64] map[Name:next_index OffsetBits:512 SizeBits:32] map[Name:acltype OffsetBits:544 SizeBits:32] map[Name:btorder OffsetBits:576 SizeBits:16] map[Name:btindex OffsetBits:592 SizeBits:16] map[Name:ipimap OffsetBits:640 SizeBits:64] map[Name:cflag OffsetBits:704 SizeBits:64] map[Name:agstart OffsetBits:768 SizeBits:64] map[Name:bxflag OffsetBits:832 SizeBits:16] map[Name:pad OffsetBits:848 SizeBits:8] map[Name:active_ag OffsetBits:856 SizeBits:8] map[Name:blid OffsetBits:864 SizeBits:16] map[Name:atlhead OffsetBits:880 SizeBits:16] map[Name:atltail OffsetBits:896 SizeBits:16] map[Name:ag_lock OffsetBits:960 SizeBits:1024] map[Name:anon_inode_list OffsetBits:1984 SizeBits:128] map[Name:rdwrlock OffsetBits:2112 SizeBits:1088] map[Name:commit_mutex OffsetBits:3200 SizeBits:1024] map[Name:xattr_sem OffsetBits:4224 SizeBits:1088] map[Name:xtlid OffsetBits:5312 SizeBits:16] map[Name:u OffsetBits:5376 SizeBits:3072] map[Name:i_dquot OffsetBits:8448 SizeBits:192] map[Name:dev OffsetBits:8640 SizeBits:32] map[Name:vfs_inode OffsetBits:8704 SizeBits:10240]]]
|
| 28/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 41933
output: 47
thoughts: 232
Thoughts: **Analyzing the JFS Inode Structure**
Okay, let's break this down. First, I'm noting that the `vfs_inode` structure is located at an offset of 8704 bits, which is equivalent to 1088 bytes. That means the `vfs_inode` is at the very end of `struct jfs_inode_info`!
Now, let's consider the `u` field. It's sitting at 5376 bits, or 672 bytes. Its size, from what I'm seeing, is 3072 bits, which is 384 bytes. So, 672 bytes + 384 bytes gives me 1056 bytes. That means `i_dquot` is immediately after `u`, at 1056 bytes, then `dev` sits at 1080 bytes, and then finally `vfs_inode` which we already figured out is at 1088 bytes.
The `vfs_inode` field is an instance of `struct inode`. Remembering that `i_sb` is at offset 40 bytes *within* `struct inode`, I can calculate that `i_sb` is positioned at offset 1088 bytes (the start of `vfs_inode`) + 40 bytes, which equals 1128 bytes from the beginning of `jfs_inode_info`. I'm missing some context on why that matters, but I know how to calculate it now.
Now, I'm left wondering what the `u` field actually *is*. I need to look into what that contains.
|
| 29/2 |
2026/05/26 00:10 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_incore.h IncludeLines:true Name:jfs_inode_info]
Results: map[SourceCode: 24: /*
25: * JFS-private inode information
26: */
27: struct jfs_inode_info {
28: int fileset; /* fileset number (always 16)*/
29: uint mode2; /* jfs-specific mode */
30: kuid_t saved_uid; /* saved for uid mount option */
31: kgid_t saved_gid; /* saved for gid mount option */
32: pxd_t ixpxd; /* inode extent descriptor */
33: dxd_t acl; /* dxd describing acl */
34: dxd_t ea; /* dxd describing ea */
35: time64_t otime; /* time created */
36: uint next_index; /* next available directory entry index */
37: int acltype; /* Type of ACL */
38: short btorder; /* access order */
39: short btindex; /* btpage entry index*/
40: struct inode *ipimap; /* inode map */
41: unsigned long cflag; /* commit flags */
42: u64 agstart; /* agstart of the containing IAG */
43: u16 bxflag; /* xflag of pseudo buffer? */
44: unchar pad;
45: signed char active_ag; /* ag currently allocating from */
46: lid_t blid; /* lid of pseudo buffer? */
47: lid_t atlhead; /* anonymous tlock list head */
48: lid_t atltail; /* anonymous tlock list tail */
49: spinlock_t ag_lock; /* protects active_ag */
50: struct list_head anon_inode_list; /* inodes having anonymous txns */
51: /*
52: * rdwrlock serializes xtree between reads & writes and synchronizes
53: * changes to special inodes. It's use would be redundant on
54: * directories since the i_mutex taken in the VFS is sufficient.
55: */
56: struct rw_semaphore rdwrlock;
57: /*
58: * commit_mutex serializes transaction processing on an inode.
59: * It must be taken after beginning a transaction (txBegin), since
60: * dirty inodes may be committed while a new transaction on the
61: * inode is blocked in txBegin or TxBeginAnon
62: */
63: struct mutex commit_mutex;
64: /* xattr_sem allows us to access the xattrs without taking i_mutex */
65: struct rw_semaphore xattr_sem;
66: lid_t xtlid; /* lid of xtree lock on directory */
67: union {
68: struct {
69: xtroot_t _xtroot; /* 288: xtree root */
70: struct inomap *_imap; /* 4: inode map header */
71: } file;
72: struct {
73: struct dir_table_slot _table[12]; /* 96: dir index */
74: dtroot_t _dtroot; /* 288: dtree root */
75: } dir;
76: struct {
77: unchar _unused[16]; /* 16: */
78: dxd_t _dxd; /* 16: */
79: /* _inline may overflow into _inline_ea when needed */
80: /* _inline_ea may overlay the last part of
81: * file._xtroot if maxentry = XTROOTINITSLOT
82: */
83: union {
84: struct {
85: /* 128: inline symlink */
86: unchar _inline[128];
87: /* 128: inline extended attr */
88: unchar _inline_ea[128];
89: };
90: unchar _inline_all[256];
91: };
92: } link;
93: } u;
94: #ifdef CONFIG_QUOTA
95: struct dquot __rcu *i_dquot[MAXQUOTAS];
96: #endif
97: u32 dev; /* will die when we get wide dev_t */
98: struct inode vfs_inode;
99: };
SourceFile:fs/jfs/jfs_incore.h]
|
| 30/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 43848
output: 44
thoughts: 125
Thoughts: **Analyzing Potential Buffer Overflows in Directory Insertion**
Okay, so I'm looking at the memory layout of `u.dir`. I see `u.dir._dtroot` is 288 bytes and `u.dir._table` is 96 bytes, for a total of 384 bytes. Now I remember `dtInsert` handles inserting entries into the directory tree. The question I'm grappling with is whether that tree is stored inline, directly within `u.dir`. If so, `dtInsert` might be writing directly to `u.dir._dtroot`.
And that's when it hit me... `dtInsert` doesn't do all the work directly, it calls `dtInsertEntry`. Could there be a situation where `dtInsertEntry` overflows the allocated space of `u.dir._dtroot`? And if that happens, the dreaded overwrite of `vfs_inode` would be a very likely consequence. I need to dive into `dtInsertEntry` immediately. This needs a closer inspection.
|
| 31/2 |
2026/05/26 00:10 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dtree.c IncludeLines:true Name:dtInsertEntry]
Results: map[SourceCode:3622: /*
3623: * dtInsertEntry()
3624: *
3625: * function: allocate free slot(s) and
3626: * write a leaf/internal entry
3627: *
3628: * return: entry slot index
3629: */
3630: static void dtInsertEntry(dtpage_t * p, int index, struct component_name * key,
3631: ddata_t * data, struct dt_lock ** dtlock)
3632: {
3633: struct dtslot *h, *t;
3634: struct ldtentry *lh = NULL;
3635: struct idtentry *ih = NULL;
3636: int hsi, fsi, klen, len, nextindex;
3637: wchar_t *kname;
3638: __le16 *name;
3639: s8 *stbl;
3640: pxd_t *xd;
3641: struct dt_lock *dtlck = *dtlock;
3642: struct lv *lv;
3643: int xsi, n;
3644: s64 bn = 0;
3645: struct metapage *mp = NULL;
3646:
3647: klen = key->namlen;
3648: kname = key->name;
3649:
3650: /* allocate a free slot */
3651: hsi = fsi = p->header.freelist;
3652: h = &p->slot[fsi];
3653: p->header.freelist = h->next;
3654: --p->header.freecnt;
3655:
3656: /* open new linelock */
3657: if (dtlck->index >= dtlck->maxcnt)
3658: dtlck = (struct dt_lock *) txLinelock(dtlck);
3659:
3660: lv = & dtlck->lv[dtlck->index];
3661: lv->offset = hsi;
3662:
3663: /* write head/only segment */
3664: if (p->header.flag & BT_LEAF) {
3665: lh = (struct ldtentry *) h;
3666: lh->next = h->next;
3667: lh->inumber = cpu_to_le32(data->leaf.ino);
3668: lh->namlen = klen;
3669: name = lh->name;
3670: if (data->leaf.ip) {
3671: len = min(klen, DTLHDRDATALEN);
3672: if (!(p->header.flag & BT_ROOT))
3673: bn = addressPXD(&p->header.self);
3674: lh->index = cpu_to_le32(add_index(data->leaf.tid,
3675: data->leaf.ip,
3676: bn, index));
3677: } else
3678: len = min(klen, DTLHDRDATALEN_LEGACY);
3679: } else {
3680: ih = (struct idtentry *) h;
3681: ih->next = h->next;
3682: xd = (pxd_t *) ih;
3683: *xd = data->xd;
3684: ih->namlen = klen;
3685: name = ih->name;
3686: len = min(klen, DTIHDRDATALEN);
3687: }
3688:
3689: UniStrncpy_to_le(name, kname, len);
3690:
3691: n = 1;
3692: xsi = hsi;
3693:
3694: /* write additional segment(s) */
3695: t = h;
3696: klen -= len;
3697: while (klen) {
3698: /* get free slot */
3699: fsi = p->header.freelist;
3700: t = &p->slot[fsi];
3701: p->header.freelist = t->next;
3702: --p->header.freecnt;
3703:
3704: /* is next slot contiguous ? */
3705: if (fsi != xsi + 1) {
3706: /* close current linelock */
3707: lv->length = n;
3708: dtlck->index++;
3709:
3710: /* open new linelock */
3711: if (dtlck->index < dtlck->maxcnt)
3712: lv++;
3713: else {
3714: dtlck = (struct dt_lock *) txLinelock(dtlck);
3715: lv = & dtlck->lv[0];
3716: }
3717:
3718: lv->offset = fsi;
3719: n = 0;
3720: }
3721:
3722: kname += len;
3723: len = min(klen, DTSLOTDATALEN);
3724: UniStrncpy_to_le(t->name, kname, len);
3725:
3726: n++;
3727: xsi = fsi;
3728: klen -= len;
3729: }
3730:
3731: /* close current linelock */
3732: lv->length = n;
3733: dtlck->index++;
3734:
3735: *dtlock = dtlck;
3736:
3737: /* terminate last/only segment */
3738: if (h == t) {
3739: /* single segment entry */
3740: if (p->header.flag & BT_LEAF)
3741: lh->next = -1;
3742: else
3743: ih->next = -1;
3744: } else
3745: /* multi-segment entry */
3746: t->next = -1;
3747:
3748: /* if insert into middle, shift right succeeding entries in stbl */
3749: stbl = DT_GETSTBL(p);
3750: nextindex = p->header.nextindex;
3751: if (index < nextindex) {
3752: memmove(stbl + index + 1, stbl + index, nextindex - index);
3753:
3754: if ((p->header.flag & BT_LEAF) && data->leaf.ip) {
3755: s64 lblock;
3756:
3757: /*
3758: * Need to update slot number for entries that moved
3759: * in the stbl
3760: */
3761: mp = NULL;
3762: for (n = index + 1; n <= nextindex; n++) {
3763: lh = (struct ldtentry *) & (p->slot[stbl[n]]);
3764: modify_index(data->leaf.tid, data->leaf.ip,
3765: le32_to_cpu(lh->index), bn, n,
3766: &mp, &lblock);
3767: }
3768: if (mp)
3769: release_metapage(mp);
3770: }
3771: }
3772:
3773: stbl[index] = hsi;
3774:
3775: /* advance next available entry index of stbl */
3776: ++p->header.nextindex;
3777: }
SourceFile:fs/jfs/jfs_dtree.c]
|
| 32/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 46484
output: 22
thoughts: 81
Thoughts: Okay, let me think this through.
**Analyzing the `dtInsertEntry` Function and Data Structures**
Alright, so `dtInsertEntry`… right, it's writing to `p->slot[fsi]`. I need to remember what `p` actually *is* in this context. Ah, yes, `p` is a `dtpage_t *`. So, a pointer to a page of directory data, or at least that's where the function is operating. Now, the crucial part: if `p` is pointing to the inline directory root, it means `p` is pointing to `u.dir._dtroot` inside the `jfs_inode_info` structure. That's the link. So `p`'s value is derived from the `jfs_inode_info` structure's directory information. Okay, so, to fully understand the flow here, I should re-familiarize myself with the definitions of `dtpage_t` and `dtroot_t`. Need to confirm how `dtpage_t` is being used and how the inline directory root is related. I'm going to consult those definitions now.
|
| 33/2 |
2026/05/26 00:10 |
tool |
codesearch-struct-layout |
0m
Error:
Args:
Results:
|
| 34/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 46870
output: 20
thoughts: 23
Thoughts: Here's my thought process, summarized as you requested:
**Navigating the Code**
Okay, so I've encountered `dtpage_t`. The way this is written, it seems to be a `typedef`. I should find where it's actually defined so I know exactly what it represents. Let's start with a quick search for `dtpage_t` throughout the codebase. That's the logical first step in understanding its purpose and how it's being used. Now, let's see what the search results turn up.
|
| 35/2 |
2026/05/26 00:10 |
tool |
grepper |
0m
Error:
Args: map[Expression:typedef.*dtpage_t]
Results:
|
| 36/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 47043
output: 18
thoughts: 26
Thoughts: Okay, here's my attempt at summarizing the thought process, as if it were my own, assuming I'm an expert in the field:
**Digging into the JFS Data Tree**
Alright, I need to get to the bottom of how JFS handles its data tree. Let's start with a specific target: `dtpage_t`. I'll immediately jump to the likely source file – `fs/jfs/jfs_dtree.h`. That header is the obvious place to find the definition, structures, and potentially some key constants or inline functions related to the data tree pages. I'm expecting to find the underlying structure that defines a data tree page; probably some kind of structure holding pointers, metadata like page numbers, and perhaps some inline functions to manipulate the structure. Knowing the data structure is key to understanding how JFS organizes its data. Let's see what's in there.
|
| 37/2 |
2026/05/26 00:10 |
tool |
grepper |
0m
Args:
Results: map[Output:fs/jfs/jfs_dtree.c=102=struct dtsplit {
--
fs/jfs/jfs_dtree.c-110-
fs/jfs/jfs_dtree.c:111:#define DT_PAGE(IP, MP) BT_PAGE(IP, MP, dtpage_t, i_dtroot)
fs/jfs/jfs_dtree.c-112-
--
fs/jfs/jfs_dtree.c=115=do { \
fs/jfs/jfs_dtree.c:116: BT_GETPAGE(IP, BN, MP, dtpage_t, SIZE, P, RC, i_dtroot); \
fs/jfs/jfs_dtree.c-117- if (!(RC)) { \
--
fs/jfs/jfs_dtree.c-134-#define DT_GETSEARCH(IP, LEAF, BN, MP, P, INDEX) \
fs/jfs/jfs_dtree.c:135: BT_GETSEARCH(IP, LEAF, BN, MP, dtpage_t, P, INDEX, i_dtroot)
fs/jfs/jfs_dtree.c-136-
--
fs/jfs/jfs_dtree.c=143=static int dtSplitPage(tid_t tid, struct inode *ip, struct dtsplit * split,
fs/jfs/jfs_dtree.c:144: struct metapage ** rmpp, dtpage_t ** rpp, pxd_t * rxdp);
fs/jfs/jfs_dtree.c-145-
--
fs/jfs/jfs_dtree.c=152=static int dtDeleteUp(tid_t tid, struct inode *ip, struct metapage * fmp,
fs/jfs/jfs_dtree.c:153: dtpage_t * fp, struct btstack * btstack);
fs/jfs/jfs_dtree.c-154-
fs/jfs/jfs_dtree.c:155:static int dtRelink(tid_t tid, struct inode *ip, dtpage_t * p);
fs/jfs/jfs_dtree.c-156-
--
fs/jfs/jfs_dtree.c=159=static int dtReadNext(struct inode *ip,
--
fs/jfs/jfs_dtree.c-161-
fs/jfs/jfs_dtree.c:162:static int dtCompare(struct component_name * key, dtpage_t * p, int si);
fs/jfs/jfs_dtree.c-163-
fs/jfs/jfs_dtree.c:164:static int ciCompare(struct component_name * key, dtpage_t * p, int si,
fs/jfs/jfs_dtree.c-165- int flag);
fs/jfs/jfs_dtree.c-166-
fs/jfs/jfs_dtree.c:167:static void dtGetKey(dtpage_t * p, int i, struct component_name * key,
fs/jfs/jfs_dtree.c-168- int flag);
fs/jfs/jfs_dtree.c-169-
fs/jfs/jfs_dtree.c:170:static int ciGetLeafPrefixKey(dtpage_t * lp, int li, dtpage_t * rp,
fs/jfs/jfs_dtree.c-171- int ri, struct component_name * key, int flag);
fs/jfs/jfs_dtree.c-172-
fs/jfs/jfs_dtree.c:173:static void dtInsertEntry(dtpage_t * p, int index, struct component_name * key,
fs/jfs/jfs_dtree.c-174- ddata_t * data, struct dt_lock **);
fs/jfs/jfs_dtree.c-175-
fs/jfs/jfs_dtree.c:176:static void dtMoveEntry(dtpage_t * sp, int si, dtpage_t * dp,
fs/jfs/jfs_dtree.c-177- struct dt_lock ** sdtlock, struct dt_lock ** ddtlock,
--
fs/jfs/jfs_dtree.c-179-
fs/jfs/jfs_dtree.c:180:static void dtDeleteEntry(dtpage_t * p, int fi, struct dt_lock ** dtlock);
fs/jfs/jfs_dtree.c-181-
fs/jfs/jfs_dtree.c:182:static void dtTruncateEntry(dtpage_t * p, int ti, struct dt_lock ** dtlock);
fs/jfs/jfs_dtree.c-183-
fs/jfs/jfs_dtree.c:184:static void dtLinelockFreelist(dtpage_t * p, int m, struct dt_lock ** dtlock);
fs/jfs/jfs_dtree.c-185-
--
fs/jfs/jfs_dtree.c=568=int dtSearch(struct inode *ip, struct component_name * key, ino_t * data,
--
fs/jfs/jfs_dtree.c-574- struct metapage *mp;
fs/jfs/jfs_dtree.c:575: dtpage_t *p;
fs/jfs/jfs_dtree.c-576- s8 *stbl;
--
fs/jfs/jfs_dtree.c=815=int dtInsert(tid_t tid, struct inode *ip,
--
fs/jfs/jfs_dtree.c-819- struct metapage *mp; /* meta-page buffer */
fs/jfs/jfs_dtree.c:820: dtpage_t *p; /* base B+-tree index page */
fs/jfs/jfs_dtree.c-821- s64 bn;
--
fs/jfs/jfs_dtree.c=926=static int dtSplitUp(tid_t tid,
--
fs/jfs/jfs_dtree.c-931- struct metapage *smp;
fs/jfs/jfs_dtree.c:932: dtpage_t *sp; /* split page */
fs/jfs/jfs_dtree.c-933- struct metapage *rmp;
fs/jfs/jfs_dtree.c:934: dtpage_t *rp; /* new right page split from sp */
fs/jfs/jfs_dtree.c-935- pxd_t rpxd; /* new right page extent descriptor */
fs/jfs/jfs_dtree.c-936- struct metapage *lmp;
fs/jfs/jfs_dtree.c:937: dtpage_t *lp; /* left child page */
fs/jfs/jfs_dtree.c-938- int skip; /* index of entry of insertion */
--
fs/jfs/jfs_dtree.c=1326=static int dtSplitPage(tid_t tid, struct inode *ip, struct dtsplit * split,
fs/jfs/jfs_dtree.c:1327: struct metapage ** rmpp, dtpage_t ** rpp, pxd_t * rpxdp)
fs/jfs/jfs_dtree.c-1328-{
--
fs/jfs/jfs_dtree.c-1330- struct metapage *smp;
fs/jfs/jfs_dtree.c:1331: dtpage_t *sp;
fs/jfs/jfs_dtree.c-1332- struct metapage *rmp;
fs/jfs/jfs_dtree.c:1333: dtpage_t *rp; /* new right page allocated */
fs/jfs/jfs_dtree.c-1334- s64 rbn; /* new right page block number */
fs/jfs/jfs_dtree.c-1335- struct metapage *mp;
fs/jfs/jfs_dtree.c:1336: dtpage_t *p;
fs/jfs/jfs_dtree.c-1337- s64 nextbn;
--
fs/jfs/jfs_dtree.c-1382-
fs/jfs/jfs_dtree.c:1383: rp = (dtpage_t *) rmp->data;
fs/jfs/jfs_dtree.c-1384- *rpp = rp;
--
fs/jfs/jfs_dtree.c=1638=static int dtExtendPage(tid_t tid,
--
fs/jfs/jfs_dtree.c-1643- struct metapage *smp, *pmp, *mp;
fs/jfs/jfs_dtree.c:1644: dtpage_t *sp, *pp;
fs/jfs/jfs_dtree.c-1645- struct pxdlist *pxdlist;
--
fs/jfs/jfs_dtree.c=1871=static int dtSplitRoot(tid_t tid,
--
fs/jfs/jfs_dtree.c-1877- struct metapage *rmp;
fs/jfs/jfs_dtree.c:1878: dtpage_t *rp;
fs/jfs/jfs_dtree.c-1879- s64 rbn;
--
fs/jfs/jfs_dtree.c=2078=int dtDelete(tid_t tid,
--
fs/jfs/jfs_dtree.c-2083- struct metapage *mp, *imp;
fs/jfs/jfs_dtree.c:2084: dtpage_t *p;
fs/jfs/jfs_dtree.c-2085- int index;
--
fs/jfs/jfs_dtree.c-2094- struct metapage *nmp;
fs/jfs/jfs_dtree.c:2095: dtpage_t *np;
fs/jfs/jfs_dtree.c-2096-
--
fs/jfs/jfs_dtree.c=2233=static int dtDeleteUp(tid_t tid, struct inode *ip,
fs/jfs/jfs_dtree.c:2234: struct metapage * fmp, dtpage_t * fp, struct btstack * btstack)
fs/jfs/jfs_dtree.c-2235-{
--
fs/jfs/jfs_dtree.c-2237- struct metapage *mp;
fs/jfs/jfs_dtree.c:2238: dtpage_t *p;
fs/jfs/jfs_dtree.c-2239- int index, nextindex;
--
fs/jfs/jfs_dtree.c-2444- */
fs/jfs/jfs_dtree.c:2445:static int dtRelink(tid_t tid, struct inode *ip, dtpage_t * p)
fs/jfs/jfs_dtree.c-2446-{
--
fs/jfs/jfs_dtree.c=2616=static int add_missing_indices(struct inode *inode, s64 bn)
--
fs/jfs/jfs_dtree.c-2623- struct metapage *mp;
fs/jfs/jfs_dtree.c:2624: dtpage_t *p;
fs/jfs/jfs_dtree.c-2625- int rc = 0;
--
fs/jfs/jfs_dtree.c=2714=int jfs_readdir(struct file *file, struct dir_context *ctx)
--
fs/jfs/jfs_dtree.c-2726- struct metapage *mp;
fs/jfs/jfs_dtree.c:2727: dtpage_t *p;
fs/jfs/jfs_dtree.c-2728- int index;
--
fs/jfs/jfs_dtree.c=3060=static int dtReadFirst(struct inode *ip, struct btstack * btstack)
--
fs/jfs/jfs_dtree.c-3065- struct metapage *mp;
fs/jfs/jfs_dtree.c:3066: dtpage_t *p;
fs/jfs/jfs_dtree.c-3067- s8 *stbl;
--
fs/jfs/jfs_dtree.c=3139=static int dtReadNext(struct inode *ip, loff_t * offset,
--
fs/jfs/jfs_dtree.c-3149- struct metapage *mp;
fs/jfs/jfs_dtree.c:3150: dtpage_t *p;
fs/jfs/jfs_dtree.c-3151- int index;
--
fs/jfs/jfs_dtree.c=3315=static int dtCompare(struct component_name * key, /* search key */
fs/jfs/jfs_dtree.c:3316: dtpage_t * p, /* directory page */
fs/jfs/jfs_dtree.c-3317- int si)
--
fs/jfs/jfs_dtree.c=3391=static int ciCompare(struct component_name * key, /* search key */
fs/jfs/jfs_dtree.c:3392: dtpage_t * p, /* directory page */
fs/jfs/jfs_dtree.c-3393- int si, /* entry slot index */
--
fs/jfs/jfs_dtree.c-3498- */
fs/jfs/jfs_dtree.c:3499:static int ciGetLeafPrefixKey(dtpage_t * lp, int li, dtpage_t * rp,
fs/jfs/jfs_dtree.c-3500- int ri, struct component_name * key, int flag)
--
fs/jfs/jfs_dtree.c-3565- */
fs/jfs/jfs_dtree.c:3566:static void dtGetKey(dtpage_t * p, int i, /* entry index */
fs/jfs/jfs_dtree.c-3567- struct component_name * key, int flag)
--
fs/jfs/jfs_dtree.c-3629- */
fs/jfs/jfs_dtree.c:3630:static void dtInsertEntry(dtpage_t * p, int index, struct component_name * key,
fs/jfs/jfs_dtree.c-3631- ddata_t * data, struct dt_lock ** dtlock)
--
fs/jfs/jfs_dtree.c-3787- */
fs/jfs/jfs_dtree.c:3788:static void dtMoveEntry(dtpage_t * sp, int si, dtpage_t * dp,
fs/jfs/jfs_dtree.c-3789- struct dt_lock ** sdtlock, struct dt_lock ** ddtlock,
--
fs/jfs/jfs_dtree.c-3988- */
fs/jfs/jfs_dtree.c:3989:static void dtDeleteEntry(dtpage_t * p, int fi, struct dt_lock ** dtlock)
fs/jfs/jfs_dtree.c-3990-{
--
fs/jfs/jfs_dtree.c-4083- */
fs/jfs/jfs_dtree.c:4084:static void dtTruncateEntry(dtpage_t * p, int ti, struct dt_lock ** dtlock)
fs/jfs/jfs_dtree.c-4085-{
--
fs/jfs/jfs_dtree.c-4163- */
fs/jfs/jfs_dtree.c:4164:static void dtLinelockFreelist(dtpage_t * p, /* directory page */
fs/jfs/jfs_dtree.c-4165- int m, /* max slot index */
--
fs/jfs/jfs_dtree.c=4244=int dtModify(tid_t tid, struct inode *ip,
--
fs/jfs/jfs_dtree.c-4249- struct metapage *mp;
fs/jfs/jfs_dtree.c:4250: dtpage_t *p;
fs/jfs/jfs_dtree.c-4251- int index;
--
fs/jfs/jfs_dtree.h=98=struct dir_table_slot {
--
fs/jfs/jfs_dtree.h-129- *
fs/jfs/jfs_dtree.h:130: * cf. dtpage_t below.
fs/jfs/jfs_dtree.h-131- */
--
fs/jfs/jfs_dtree.h=180=typedef union {
--
fs/jfs/jfs_dtree.h-197- struct dtslot slot[128];
fs/jfs/jfs_dtree.h:198:} dtpage_t;
fs/jfs/jfs_dtree.h-199-
--
fs/jfs/jfs_imap.c=581=int diWrite(tid_t tid, struct inode *ip)
--
fs/jfs/jfs_imap.c-743- else if (type & tlckDTREE) {
fs/jfs/jfs_imap.c:744: dtpage_t *p, *xp;
fs/jfs/jfs_imap.c-745-
--
fs/jfs/jfs_imap.c-748- */
fs/jfs/jfs_imap.c:749: p = (dtpage_t *) &jfs_ip->i_dtroot;
fs/jfs/jfs_imap.c:750: xp = (dtpage_t *) & dp->di_dtroot;
fs/jfs/jfs_imap.c-751- lv = ilinelock->lv;
]
|
| 38/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 52079
output: 21
thoughts: 47
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of some data structure design:
**Decoding the Data Structure's Blueprint**
Right, let me see... I'm looking at `dtpage_t`. Ah, it's a union, and apparently, it's designed to hold 128 elements. Now, what's throwing me a bit is the size of the individual elements. Hang on, the `sizeof(struct dtslot)`... that's 32 bytes! That raises a question, if a single `dtslot` is 32 bytes, a `dtpage_t` holding 128 would be 32*128 bytes, which seems to imply that each item can be as big as 32*128 bytes. This doesn't make sense, it must be some kind of array of size 128 of `dtslot`. Let me dive in and check the definition of `struct dtslot` itself, confirm this, and see if I'm missing something crucial in its internal structure. I need to understand how these slots relate to the overall page structure.
|
| 39/2 |
2026/05/26 00:10 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:next OffsetBits:0 SizeBits:8] map[Name:cnt OffsetBits:8 SizeBits:8] map[Name:name OffsetBits:16 SizeBits:240]]]
|
| 40/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 52465
output: 20
thoughts: 74
Thoughts: Okay, let me break this down.
**Diving into DTSlot and DTPages**
Alright, so `sizeof(struct dtslot)` is apparently 32 bytes, which translates to 256 bits. That's good to know. Now, since `dtpage_t` is defined as an array of these `dtslot` structures, 128 of them in fact, a single `dtpage_t` should be `128 * 32 = 4096` bytes. That makes intuitive sense.
Hold on a second... the `u.dir._dtroot` member is reported as being 288 bytes. That seems awfully small in comparison! Something's not adding up. I'd better double-check the definition of `dtroot_t` to see what's actually going on in there and figure out where this size difference is coming from. Time to dig deeper into its structure.
|
| 41/2 |
2026/05/26 00:10 |
tool |
codesearch-struct-layout |
0m
Error:
Args:
Results:
|
| 42/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 52788
output: 20
thoughts: 11
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and presented as if it were my own internal monologue:
**Investigating `dtroot_t`**
Alright, time to get to work. First, the immediate trigger is a need to understand the concept of `dtroot_t`. This suggests, at a minimum, I'm dealing with a data structure or function related to some root element. Based on the naming convention, which includes `dt` which is probably short for "data type" or "data tree", and `root` this is very likely a data structure or object used to describe the root of some kind of hierarchical data structure. Now the `_t` suffix is generally associated with type definitions in C/C++. Therefore, I'm expecting this to be a structure or type declaration in C/C++. I'll need to know whether the usage or definition is known or unknown. Now, I have to figure out what context I'm in to start investigating the search terms, which context will make all the difference. Is this a custom data structure in some specific project, or is this a standardized one? I'll probably start with a general search, and then narrow my focus based on what I find.
|
| 43/2 |
2026/05/26 00:10 |
tool |
grepper |
0m
Error:
Args: map[Expression:typedef.*dtroot_t]
Results:
|
| 44/2 |
2026/05/26 00:10 |
llm |
expert |
0m
Model:
Tokens:
input: 53096
output: 18
thoughts: 26
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Investigating `dtroot_t` in the JFS dtree Implementation**
Right, let's dive in. I need to refresh my memory on the specifics of how JFS manages its directory trees, specifically that data structure. My immediate instinct is to pinpoint where `dtroot_t` is defined. The most logical place to start is within the JFS filesystem code itself, and, given its likely role in directory management, I'd expect it to be in one of the dtree-related headers. So, let's get the search underway. I'll begin by looking in `fs/jfs/jfs_dtree.h`. That seems like the most promising spot, and should give me the core definition of the struct, its members, and any associated macros or inline functions that operate on it. Knowing that will be the foundational information I need to understand its use within the larger filesystem context.
|
| 45/2 |
2026/05/26 00:11 |
tool |
grepper |
0m
Args:
Results: map[Output:fs/jfs/jfs_dinode.h=22=struct dinode {
--
fs/jfs/jfs_dinode.h-80-
fs/jfs/jfs_dinode.h:81: dtroot_t _dtroot; /* 288: dtree root */
fs/jfs/jfs_dinode.h-82- } _dir; /* (384) */
--
fs/jfs/jfs_dtree.c=1871=static int dtSplitRoot(tid_t tid,
--
fs/jfs/jfs_dtree.c-1875- struct metapage *smp;
fs/jfs/jfs_dtree.c:1876: dtroot_t *sp;
fs/jfs/jfs_dtree.c-1877- struct metapage *rmp;
--
fs/jfs/jfs_dtree.c=2524=void dtInitRoot(tid_t tid, struct inode *ip, u32 idotdot)
--
fs/jfs/jfs_dtree.c-2526- struct jfs_inode_info *jfs_ip = JFS_IP(ip);
fs/jfs/jfs_dtree.c:2527: dtroot_t *p;
fs/jfs/jfs_dtree.c-2528- int fsi;
--
fs/jfs/jfs_dtree.h=132=typedef union {
--
fs/jfs/jfs_dtree.h-146- struct dtslot slot[9];
fs/jfs/jfs_dtree.h:147:} dtroot_t;
fs/jfs/jfs_dtree.h-148-
--
fs/jfs/jfs_dtree.h=180=typedef union {
--
fs/jfs/jfs_dtree.h-221-#define DT_GETSTBL(p) ( ((p)->header.flag & BT_ROOT) ?\
fs/jfs/jfs_dtree.h:222: ((dtroot_t *)(p))->header.stbl : \
fs/jfs/jfs_dtree.h-223- (s8 *)&(p)->slot[(p)->header.stblindex] )
--
fs/jfs/jfs_incore.h=27=struct jfs_inode_info {
--
fs/jfs/jfs_incore.h-73- struct dir_table_slot _table[12]; /* 96: dir index */
fs/jfs/jfs_incore.h:74: dtroot_t _dtroot; /* 288: dtree root */
fs/jfs/jfs_incore.h-75- } dir;
]
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| 46/2 |
2026/05/26 00:11 |
llm |
expert |
0m
Model:
Tokens:
input: 54077
output: 45
thoughts: 862
Thoughts: **Vulnerability Analysis of Potential Out-of-Bounds Write in JFS Inline Directories**
Okay, let's break this down. First, the `dtroot_t` structure. It's a union containing nine slots, each 32 bytes, for a total size of 288 bytes. I see that `dtInsert` is casting a `dtroot_t` to a `dtpage_t`. That looks suspicious. This macro `DT_GETSEARCH` uses `dtpage_t` when dealing with `p`, which in certain scenarios is `dtroot_t`.
My immediate concern is the `dtInsertEntry` function. It uses `p->slot[fsi]`, and if `fsi` (the free slot index) goes out of bounds – say, greater than 8 – it could lead to an out-of-bounds write, past the 288-byte boundary of `dtroot_t`. The code uses `p->header.freelist` to track free slots. The crucial point here is that `p->header.freecnt` should, at most, be 8 if `p` is `dtroot_t`.
Now, the `dtInsert` function checks `n > p->header.freecnt`. If this condition is *true*, it triggers a `dtSplitUp` call. However, if `n` is *less than or equal to* `p->header.freecnt`, it proceeds to `dtInsertEntry`. My concern is what if `p->header.freecnt` is corrupted and contains a value greater than 8? That's the key to this.
That's the flaw! This reproducer uses a crafted JFS image. This means the image is specifically made to have a corrupted `freecnt` in an inline directory root, allowing for out-of-bounds writes.
Let me verify the offsets and memory layout. I'm looking at `dtroot_t` within `jfs_inode_info`. The vulnerable structure, `u.dir._dtroot`, is at offset 96 within `u.dir`. Also `u.dir` is at offset 672 in the `jfs_inode_info`. The size of `u.dir._table` is 96 bytes and the size of `u.dir._dtroot` is 288 bytes. Consequently `u.dir._dtroot` ends at `672 + 96 + 288 = 1056` bytes. Following this is `i_dquot` starting at offset 1056, `dev` starting at offset 1080 and `vfs_inode` starting at offset 1088.
So, if `fsi` is large, `p->slot[fsi]` will write to `u.dir._dtroot + fsi * 32`. If `fsi` is, say, 13, then `13 * 32 = 416`. This means the write will be `416 - 288 = 128` bytes past the end of `_dtroot`, which is at `1056 + 128 = 1184`. However, `vfs_inode` starts at offset 1088. Its `i_sb` field starts at offset 40, so `i_sb` begins at offset `1088 + 40 = 1128`. Relative to `_dtroot`, that's at `1128 - 1056 = 72` bytes.
Crucially, let's verify that `p->slot` starts at offset 0 of `dtroot_t` and confirms my current understanding.
|
| 47/2 |
2026/05/26 00:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dtree.h IncludeLines:true Name:dtroot_t]
Results: map[SourceCode: 127: /*
128: * directory root page (in-line in on-disk inode):
129: *
130: * cf. dtpage_t below.
131: */
132: typedef union {
133: struct {
134: struct dasd DASD; /* 16: DASD limit/usage info */
135:
136: u8 flag; /* 1: */
137: u8 nextindex; /* 1: next free entry in stbl */
138: s8 freecnt; /* 1: free count */
139: s8 freelist; /* 1: freelist header */
140:
141: __le32 idotdot; /* 4: parent inode number */
142:
143: s8 stbl[8]; /* 8: sorted entry index table */
144: } header; /* (32) */
145:
146: struct dtslot slot[9];
147: } dtroot_t;
SourceFile:fs/jfs/jfs_dtree.h]
|
| 48/2 |
2026/05/26 00:11 |
llm |
expert |
0m
Model:
Tokens:
input: 56146
output: 44
thoughts: 455
Thoughts: **Analyzing the `slot` Structure and Potential Buffer Overflows**
Okay, so `slot` is an array – a very specific one, an array of nine `dtslot` structures, to be precise. And from what I see, `slot[0]` is the header. The interesting part, though, is that `slot[1]` through `slot[8]` are the actual data slots where the important stuff lives. Right now I'm focusing on the index `fsi`, which represents an index into this `slot` array. The maximum valid value for `fsi` appears to be 8, which makes sense given the array size. If `fsi` exceeds 8, that's where things get concerning because we're looking at writing past the end of the `slot` array and into whatever memory comes next. That could lead to all sorts of nasty side effects, like data corruption or even security vulnerabilities, such as a buffer overflow.
Now I need to remember, `i_sb` is located at offset 72 from the end of a `dtroot_t` structure. So, if we know the size of `dtroot_t` is 288 bytes, then `i_sb` is at `288 + 72 = 360` bytes from the start of the `dtroot_t` structure. This also means that if we divide that offset, we should be able to deduce in which `slot` `i_sb` lies; `360 / 32 = 11.25`. So `slot[11]` would be at the offset `11 * 32 = 352` within the `dtroot_t`. From this, we can deduce that `slot[11].name` is at offset `352 + 16 = 368`.
Hold on a second, though. I think I'm getting mixed up here. `i_sb` is at offset 360, while `slot[11].name` starts at 368. Something's not quite aligning. What about the other members of `slot[11]`? Let me think: `slot[11].next` and `slot[11].cnt`, where are they? `slot[11].next` is at offset 352 (the beginning of `slot[11]`), and `slot[11].cnt` should be at 353. But `i_sb` is 8 bytes, so it goes from 360 to 367. Is that the case?
Okay, I need to make sure I understand the memory layout correctly. `slot[11]` starts at 352. The `name` field of `slot[11]` starts at 368. Thus, 360 is in the middle of `slot[11].name`? No, no, `name` is at an offset of 16 within the structure, so I'm making a mistake somewhere. Let me re-evaluate, since the structure size, based on the structure layout, is 32 bytes... I should double-check the `struct dtslot` definition to be sure. It looks like it should be the case. So, `next` is probably one byte, `cnt` is one byte, and `name` is likely 30 bytes. I need to go back and check the definition of `struct dtslot` to confirm all these assumptions.
|
| 49/2 |
2026/05/26 00:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dtree.h IncludeLines:true Name:dtslot]
Results: map[SourceCode: 24: /*
25: * entry segment/slot
26: *
27: * an entry consists of type dependent head/only segment/slot and
28: * additional segments/slots linked vi next field;
29: * N.B. last/only segment of entry is terminated by next = -1;
30: */
31: /*
32: * directory page slot
33: */
34: struct dtslot {
35: s8 next; /* 1: */
36: s8 cnt; /* 1: */
37: __le16 name[15]; /* 30: */
38: }; /* (32) */
SourceFile:fs/jfs/jfs_dtree.h]
|
| 50/2 |
2026/05/26 00:11 |
llm |
expert |
0m
Model:
Tokens:
input: 57636
output: 44
thoughts: 388
Thoughts: **Analyzing the Memory Layout and String Overlap**
Okay, so `name` takes up 30 bytes. That much is clear. Given that, if we're looking at `slot[11]`, it starts at offset 352. `slot[11].next` is at 352, `slot[11].cnt` is at 353, and then `slot[11].name` spans from 354 to 383. Therefore, `i_sb` which occupies bytes 360-367, is *inside* `slot[11].name`!
Aha! `dtInsertEntry` is responsible for writing the filename into `slot[fsi].name` – confirmed by that `UniStrncpy_to_le` call. And the filename in question here is "cpuacct.usage_percpu". We need to understand how *that* string interacts with the `i_sb` region.
`kname` is indeed the filename. If `fsi` (file system index) is 11, then the filename is written into `slot[11].name`, which begins at 354. `i_sb` is at 360, placing it at an offset of 6 within `slot[11].name`.
Now, if we consider "cpuacct.usage_percpu", at offset 6, the string contains the 4th character. Okay, but wait, the string is converted to UTF-16LE, so *each* character now occupies two bytes. That means the `i_sb` region overlaps with the *fourth* character of the UTF-16LE encoded filename. The string is "cpuacct.usage_percpu" so the 4th character is 'a'. If this is the first slot, then it's a `ldtentry` entry. Let's dig into the `ldtentry` definition. This is the crucial point for the analysis.
|
| 51/2 |
2026/05/26 00:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dtree.h IncludeLines:true Name:ldtentry]
Results: map[SourceCode: 67: /*
68: * leaf node entry head/only segment
69: *
70: * For legacy filesystems, name contains 13 wchars -- no index field
71: */
72: struct ldtentry {
73: __le32 inumber; /* 4: 4-byte aligned */
74: s8 next; /* 1: */
75: u8 namlen; /* 1: */
76: __le16 name[11]; /* 22: 2-byte aligned */
77: __le32 index; /* 4: index into dir_table */
78: }; /* (32) */
SourceFile:fs/jfs/jfs_dtree.h]
|
| 52/2 |
2026/05/26 00:11 |
llm |
expert |
0m
Model:
Tokens:
input: 58737
output: 24
thoughts: 984
Thoughts: **Decoding the Data Structure's Overwrite**
Okay, let's break this down systematically. I see an `ldtentry` structure. It's got the usual suspects: `inumber` (4 bytes), `next` (1 byte), `namlen` (1 byte), `name` (22 bytes), and an `index` (4 bytes). So the `name` field starts at offset 6. I'm focusing on how "rcpu" is overwriting part of a string, specifically related to the "cpuacct.usage_percpu" name.
Knowing that `slot[11]` begins at address 352, and the `ldtentry`'s `name` field begins at offset 6, the `name` field within this `ldtentry` starts at 358. Now, if `i_sb` is located at offset 360, it appears to be at offset 2 within the `ldtentry.name` field. So, the second character of the string, which, if it's the first slot would be 'p', but it looks like the `i_sb` has been overwritten by "rcpu". This clearly indicates that the string "cpuacct.usage_percpu" is taking more than one slot.
The full string "cpuacct.usage_percpu" is 20 characters long. With the first slot potentially holding 11 characters (or less). That means we're dealing with at least a second slot, most likely, maybe more.
Let's assume the remaining string is handled by the second slot (`dtslot`). It seems to have `next` (1 byte), `cnt` (1 byte), and `name` (30 bytes). The `name` within `dtslot` is at offset 2. Now, if this `dtslot` is `slot[11]` starting at address 352, then `dtslot.name` begins at offset 354. `i_sb` located at offset 360, will correspond to offset 6 within the name field of `dtslot`.
The remaining part of the string would be "ge_percpu" (20 - 11 = 9 characters). Given that "cpuacct.usa" uses up 11 characters of the 20 character string, "ge_percpu" accounts for the remaining 9 characters. If we're looking at offset 6 in `dtslot.name`, we need to account for what is there. This would be the 4th character of "ge_percpu", which should be 'p'. So characters at offsets 6, 8, 10, 12 of `dtslot.name` should be 'p', 'e', 'r', 'c'.
Now, let's look at the "wild pointer" `0075007000630072`. `72` is 'r', `63` is 'c', `70` is 'p', `75` is 'u'. So it reads as "rcpu". Now, "rcpu" is the end of the string. So these characters should align with characters from the end of the remaining string "ge_percpu". The offset within the remaining string is then: g (0), e (1), _ (2), p (3), e (4), r (5), c (6), p (7), u (8). "rcpu" starts at index 5 and goes through 8.
Index 5 corresponds to offset `5 * 2 = 10` of `dtslot.name`. Therefore "rcpu" is at offset 10 of `dtslot.name`. Since `dtslot.name` begins at offset 2 of `dtslot`, "rcpu" is located at offset 12 of `dtslot`.
If `i_sb` (the pointer that's being overwritten) is located at offset 12 within a slot, then the slot would begin at `360 - 12 = 348`. But here's the rub - slots are 32-byte aligned, and 348 is not a multiple of 32! I must be making an error in calculating the offsets. I need to revisit the actual layouts and verify these calculations. I'll need to double check the precise offset of `i_sb` with reference to `jfs_inode_info`.
|
| 53/2 |
2026/05/26 00:11 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:fileset OffsetBits:0 SizeBits:32] map[Name:mode2 OffsetBits:32 SizeBits:32] map[Name:saved_uid OffsetBits:64 SizeBits:32] map[Name:saved_gid OffsetBits:96 SizeBits:32] map[Name:ixpxd OffsetBits:128 SizeBits:64] map[Name:acl OffsetBits:192 SizeBits:128] map[Name:ea OffsetBits:320 SizeBits:128] map[Name:otime OffsetBits:448 SizeBits:64] map[Name:next_index OffsetBits:512 SizeBits:32] map[Name:acltype OffsetBits:544 SizeBits:32] map[Name:btorder OffsetBits:576 SizeBits:16] map[Name:btindex OffsetBits:592 SizeBits:16] map[Name:ipimap OffsetBits:640 SizeBits:64] map[Name:cflag OffsetBits:704 SizeBits:64] map[Name:agstart OffsetBits:768 SizeBits:64] map[Name:bxflag OffsetBits:832 SizeBits:16] map[Name:pad OffsetBits:848 SizeBits:8] map[Name:active_ag OffsetBits:856 SizeBits:8] map[Name:blid OffsetBits:864 SizeBits:16] map[Name:atlhead OffsetBits:880 SizeBits:16] map[Name:atltail OffsetBits:896 SizeBits:16] map[Name:ag_lock OffsetBits:960 SizeBits:1024] map[Name:anon_inode_list OffsetBits:1984 SizeBits:128] map[Name:rdwrlock OffsetBits:2112 SizeBits:1088] map[Name:commit_mutex OffsetBits:3200 SizeBits:1024] map[Name:xattr_sem OffsetBits:4224 SizeBits:1088] map[Name:xtlid OffsetBits:5312 SizeBits:16] map[Name:u OffsetBits:5376 SizeBits:3072] map[Name:i_dquot OffsetBits:8448 SizeBits:192] map[Name:dev OffsetBits:8640 SizeBits:32] map[Name:vfs_inode OffsetBits:8704 SizeBits:10240]]]
|
| 54/2 |
2026/05/26 00:11 |
llm |
expert |
0m
Model:
Tokens:
input: 61403
output: 47
thoughts: 764
Thoughts: **Decoding the Data Structure Mishap**
Okay, let's break this down. I'm looking at how `i_sb` relates to `_dtroot` within this `jfs_inode_info` structure. My starting point is the offsets. `u` is at 672 bytes, `vfs_inode` is at 1088 bytes, and `i_sb` sits 40 bytes into `vfs_inode`. That puts `i_sb` at 1128 bytes from the beginning. `_dtroot` within `u` is at 768 bytes (672 + 96).
The critical difference is 360 bytes. Dividing that by 32 (the size of each `dtslot`) gives us 11 slots and a remainder of 8. So, `i_sb` should be at offset 8 within `slot[11]`. Now, the structure of `dtslot` is `next`, `cnt`, and `name`. My concern is that, since my offset is within the `name` field, specifically at offset 8, and the offset within that is 6, what characters are there?
Let me investigate that...
Given that the characters are: 'p', 'e', 'r', 'c'... but wait! The correct data is 'r', 'c', 'p', 'u'.
If I convert those to hex, it's `0063007200650070`. But the wild pointer shows `0075007000630072`. This suggests a 'rcpu' as the answer. Why is the order reversed to 'rcpu'?
Back to the string splitting. The original filename is "cpuacct.usage_percpu," so the length is 20. But, `dtInsertEntry` uses `min(klen, DTLHDRDATALEN)`. I need to figure out what `DTLHDRDATALEN` is and verify that it explains this reverse byte order! There's a mismatch between my expected bytes and the actual value. This is a critical puzzle piece!
|
| 55/2 |
2026/05/26 00:11 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:fs/jfs/jfs_dtree.h IncludeLines:true Name:DTLHDRDATALEN]
Results: map[SourceCode: SourceFile:]
|
| 56/2 |
2026/05/26 00:11 |
llm |
expert |
0m
Model:
Tokens:
input: 62711
output: 22
thoughts: 13
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing the Query: DTLHDRDATALEN**
Alright, let's dive in. The presence of `DTLHDRDATALEN` immediately screams a few things to me. This suggests we're likely dealing with some form of data transfer, possibly a protocol or data structure used in a system that involves the `DTL` prefix. The `HDR` implies a header component, and `DATALEN`, of course, denotes a length field for the data that follows. I wonder about the environment this is running in, or the specific use case, could be a network protocol, a file format, or an internal memory structure? I'll probably start by looking for its definition in the code or documentation. I'll need to understand what it's used for. Does it align with the expected behavior of the system? Are there any obvious security implications associated with a length field? I wonder if there might be vulnerabilities there. I should search for the definition first, and then trace its use to gain a solid understanding.
|
| 57/2 |
2026/05/26 00:12 |
tool |
grepper |
0m
Args: map[Expression:#define DTLHDRDATALEN]
Results: map[Output:fs/jfs/jfs_dtree.h=72=struct ldtentry {
--
fs/jfs/jfs_dtree.h-80-#define DTLHDRSIZE 6
fs/jfs/jfs_dtree.h:81:#define DTLHDRDATALEN_LEGACY 13 /* Old (OS/2) format */
fs/jfs/jfs_dtree.h:82:#define DTLHDRDATALEN 11
fs/jfs/jfs_dtree.h-83-
]
|
| 58/2 |
2026/05/26 00:12 |
llm |
expert |
0m
Model:
Tokens:
input: 63122
output: 19
thoughts: 412
Thoughts: **Analyzing Data Structure Offsets**
Okay, so `DTLHDRDATALEN` is confirmed as 11. That means the first slot, or `slot[0]`, takes up 11 characters. The string we're dealing with is "cpuacct.usage_percpu". The first 11 characters are "cpuacct.usa". That leaves us with "ge_percpu" for the second part. The second slot is `dtslot`. `dtslot`'s `name` field is defined as 15 `__le16` characters, but we only have 9 remaining characters, "ge_percpu".
Now, here's where it gets interesting. I'm trying to figure out the offset of `i_sb` within the context of `dtslot`. I've noted that `i_sb` is at offset 8 of `slot[11]`, and offset 8 of `dtslot` translates to offset 6 of the `name` field, as `dtslot` is the `name` field. So, starting from index 3, we have 'p', 'e', 'r', 'c'. However, the wild pointer is "rcpu", which are the characters at indices 5, 6, 7, and 8. Hmm, that's offset by two characters or four bytes. Why?
I think my initial assumption about `i_sb`'s location is off, and should re-verify that within the `struct inode` definition. I need to make sure I am accounting for padding in the structure. The offset of `vfs_inode` is at 1088, and `i_sb` is at offset 40 inside `vfs_inode`, so let me double-check the layout of `struct inode`. I need to revisit that structure definition and map out the members again.
|
| 59/2 |
2026/05/26 00:12 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:i_mode OffsetBits:0 SizeBits:16] map[Name:i_opflags OffsetBits:16 SizeBits:16] map[Name:i_uid OffsetBits:32 SizeBits:32] map[Name:i_gid OffsetBits:64 SizeBits:32] map[Name:i_flags OffsetBits:96 SizeBits:32] map[Name:i_acl OffsetBits:128 SizeBits:64] map[Name:i_default_acl OffsetBits:192 SizeBits:64] map[Name:i_op OffsetBits:256 SizeBits:64] map[Name:i_sb OffsetBits:320 SizeBits:64] map[Name:i_mapping OffsetBits:384 SizeBits:64] map[Name:i_security OffsetBits:448 SizeBits:64] map[Name:i_ino OffsetBits:512 SizeBits:64] map[Name: OffsetBits:576 SizeBits:32] map[Name:i_rdev OffsetBits:608 SizeBits:32] map[Name:i_size OffsetBits:640 SizeBits:64] map[Name:i_atime_sec OffsetBits:704 SizeBits:64] map[Name:i_mtime_sec OffsetBits:768 SizeBits:64] map[Name:i_ctime_sec OffsetBits:832 SizeBits:64] map[Name:i_atime_nsec OffsetBits:896 SizeBits:32] map[Name:i_mtime_nsec OffsetBits:928 SizeBits:32] map[Name:i_ctime_nsec OffsetBits:960 SizeBits:32] map[Name:i_generation OffsetBits:992 SizeBits:32] map[Name:i_lock OffsetBits:1024 SizeBits:1024] map[Name:i_bytes OffsetBits:2048 SizeBits:16] map[Name:i_blkbits OffsetBits:2064 SizeBits:8] map[Name:i_write_hint OffsetBits:2072 SizeBits:8] map[Name:i_blocks OffsetBits:2112 SizeBits:64] map[Name:i_state OffsetBits:2176 SizeBits:32] map[Name:i_rwsem OffsetBits:2240 SizeBits:1088] map[Name:dirtied_when OffsetBits:3328 SizeBits:64] map[Name:dirtied_time_when OffsetBits:3392 SizeBits:64] map[Name:i_hash OffsetBits:3456 SizeBits:128] map[Name:i_io_list OffsetBits:3584 SizeBits:128] map[Name:i_wb OffsetBits:3712 SizeBits:64] map[Name:i_wb_frn_winner OffsetBits:3776 SizeBits:32] map[Name:i_wb_frn_avg_time OffsetBits:3808 SizeBits:16] map[Name:i_wb_frn_history OffsetBits:3824 SizeBits:16] map[Name:i_lru OffsetBits:3840 SizeBits:128] map[Name:i_sb_list OffsetBits:3968 SizeBits:128] map[Name:i_wb_list OffsetBits:4096 SizeBits:128] map[Name: OffsetBits:4224 SizeBits:128] map[Name:i_version OffsetBits:4352 SizeBits:64] map[Name:i_sequence OffsetBits:4416 SizeBits:64] map[Name:i_count OffsetBits:4480 SizeBits:32] map[Name:i_dio_count OffsetBits:4512 SizeBits:32] map[Name:i_writecount OffsetBits:4544 SizeBits:32] map[Name:i_readcount OffsetBits:4576 SizeBits:32] map[Name: OffsetBits:4608 SizeBits:64] map[Name:i_flctx OffsetBits:4672 SizeBits:64] map[Name:i_data OffsetBits:4736 SizeBits:5120] map[Name: OffsetBits:9856 SizeBits:128] map[Name: OffsetBits:9984 SizeBits:64] map[Name:i_fsnotify_mask OffsetBits:10048 SizeBits:32] map[Name:i_fsnotify_marks OffsetBits:10112 SizeBits:64] map[Name:i_private OffsetBits:10176 SizeBits:64]]]
|
| 60/2 |
2026/05/26 00:12 |
llm |
expert |
0m
Model:
Tokens:
input: 65222
output: 24
thoughts: 96
Thoughts: **Navigating the JFS Inode Structure**
Okay, so I'm diving into this JFS inode layout. Hold on... I'm seeing `i_sb` is supposed to be at offset 320 bits, or 40 bytes. But, hang on a second, is `CONFIG_SECURITY` enabled in this kernel config? Because if it *is*, then things shift. `i_security` gets inserted and it's taking up space at 448 bits, which is 56 bytes. Alright, I need to double-check that offset for `i_sb` again. I need to refresh my understanding of the `jfs_inode_info` structure layout. Let's make sure I didn't miss something fundamental here.
|
| 61/2 |
2026/05/26 00:12 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:fileset OffsetBits:0 SizeBits:32] map[Name:mode2 OffsetBits:32 SizeBits:32] map[Name:saved_uid OffsetBits:64 SizeBits:32] map[Name:saved_gid OffsetBits:96 SizeBits:32] map[Name:ixpxd OffsetBits:128 SizeBits:64] map[Name:acl OffsetBits:192 SizeBits:128] map[Name:ea OffsetBits:320 SizeBits:128] map[Name:otime OffsetBits:448 SizeBits:64] map[Name:next_index OffsetBits:512 SizeBits:32] map[Name:acltype OffsetBits:544 SizeBits:32] map[Name:btorder OffsetBits:576 SizeBits:16] map[Name:btindex OffsetBits:592 SizeBits:16] map[Name:ipimap OffsetBits:640 SizeBits:64] map[Name:cflag OffsetBits:704 SizeBits:64] map[Name:agstart OffsetBits:768 SizeBits:64] map[Name:bxflag OffsetBits:832 SizeBits:16] map[Name:pad OffsetBits:848 SizeBits:8] map[Name:active_ag OffsetBits:856 SizeBits:8] map[Name:blid OffsetBits:864 SizeBits:16] map[Name:atlhead OffsetBits:880 SizeBits:16] map[Name:atltail OffsetBits:896 SizeBits:16] map[Name:ag_lock OffsetBits:960 SizeBits:1024] map[Name:anon_inode_list OffsetBits:1984 SizeBits:128] map[Name:rdwrlock OffsetBits:2112 SizeBits:1088] map[Name:commit_mutex OffsetBits:3200 SizeBits:1024] map[Name:xattr_sem OffsetBits:4224 SizeBits:1088] map[Name:xtlid OffsetBits:5312 SizeBits:16] map[Name:u OffsetBits:5376 SizeBits:3072] map[Name:i_dquot OffsetBits:8448 SizeBits:192] map[Name:dev OffsetBits:8640 SizeBits:32] map[Name:vfs_inode OffsetBits:8704 SizeBits:10240]]]
|
| 62/2 |
2026/05/26 00:12 |
llm |
expert |
0m
Model:
Tokens:
input: 66173
output: 40
thoughts: 1091
Thoughts: **Analyzing Potential File System Corruption**
Okay, let's break this down. My initial calculations show `vfs_inode` starts at offset 1088 bytes. I need to verify that. I see `u` is at 672 bytes, and `u.dir._dtroot` is at 768 bytes, ending at 1056 bytes. `i_dquot` starts at 1056 bytes, then `dev` at 1080 bytes, and finally, `vfs_inode` should be at 1088. But why?
Now, `i_sb` resides at offset 40 *within* `vfs_inode`. So, that should put `i_sb` at 1128 bytes (1088 + 40). Let's see: `1128 - 768 = 360`, and `360 / 32 = 11.25`, meaning it's the 8th byte of the 12th entry, `slot[11]`, which should start at 1120 bytes. That makes sense. `slot[11]` is a `dtslot`, containing `next`, `cnt`, and `name`. My analysis shows the second part of the filename "cpuacct.usage_percpu" is written into `slot[11].name`. But wait, `dtInsertEntry` uses chunks.
The first chunk is "cpuacct.usa" (11 chars). It then writes the string to "ge_percpu" (9 chars). But, is it *always* `slot[11]`? No, it uses `slot[fsi]`, where `fsi` comes from `p->header.freelist`. If the freelist is corrupted, I could get `fsi == 11`. That would mean I'm writing the second chunk ("ge_percpu") to `slot[11]`.
The second chunk, "ge_percpu" gets written into `slot[11].name` starting at offset 6. Each character is two bytes (`__le16`), so index 3 of `name`. Index 3, then starts with 'p' in "percpu". So I get 'p', 'e', 'r', 'c'. However, the wild pointer reads "rcpu". The letters "rcpu" exist at index 5, 6, 7, 8.
Index 5 corresponds to offset 10 of `name`, and offset 12 of `dtslot`. This means if `i_sb` is at offset 12 of `dtslot`, then it is at `1120 + 12 = 1132`. Which is wrong! I previously calculated it as 1128. I got to check that again.
Let's rethink this. `i_dquot` is an array of pointers, `MAXQUOTAS` pointers, and each pointer takes 8 bytes. `i_dquot` starts at 1056. I previously calculated the size of `i_dquot` as `3 * 8 = 24` bytes. `1056 + 24 = 1080`. Then `dev` is a `u32` (4 bytes). So `dev` ends at 1084. Why does `vfs_inode` start at 1088? Because `struct inode` is 8 byte aligned, so it's a 4-byte padding there.
Now, could I be wrong about `MAXQUOTAS`? I need to verify that constant.
|
| 63/2 |
2026/05/26 00:12 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:include/linux/quota.h IncludeLines:true Name:MAXQUOTAS]
Results: map[SourceCode: SourceFile:]
|
| 64/2 |
2026/05/26 00:12 |
llm |
expert |
0m
Model:
Tokens:
input: 68140
output: 20
thoughts: 11
Thoughts: Here's my thought process, summarized as you requested:
**Navigating the Digital Landscape for `MAXQUOTAS`**
Okay, I need to find something. The term that's coming to mind is `MAXQUOTAS`. My brain is immediately going into search mode, assuming this is likely a specific variable, setting, or command within some system. I need to figure out what context I'm in - Is this a database, a cloud service, an operating system, or something else entirely? The specificity of `MAXQUOTAS` suggests it's not a general concept. It's likely a configuration value.
I’m already starting to mentally categorize possible search strategies. I could start with a web search - but that's a bit broad without a more targeted context. A more efficient approach might be looking at my personal notes and configuration files. Do I recall encountering this keyword in any past projects or documentation? If it is a recent variable, I'll examine the immediate past for context. If not, I will initiate a comprehensive search of past documentation, using search parameters and logical search functions. If this is a very important variable, I should probably search any system documentation or source code repositories for this term as the first line of investigation.
|
| 65/2 |
2026/05/26 00:12 |
tool |
grepper |
0m
Args: map[Expression:#define MAXQUOTAS]
Results: map[Output:include/uapi/linux/quota.h-39-
include/uapi/linux/quota.h:40:#define MAXQUOTAS 3
include/uapi/linux/quota.h-41-#define USRQUOTA 0 /* element used for user quotas */
]
|
| 66/2 |
2026/05/26 00:12 |
llm |
expert |
0m
Model:
Tokens:
input: 68512
output: 43
thoughts: 451
Thoughts: **Analyzing Potential Inconsistencies in Data Structure Offsets**
Okay, so `MAXQUOTAS` is set to 3. But hang on, what happens if `CONFIG_QUOTA` is disabled? If quota support is off, then `i_dquot` doesn't even exist in the `inode` structure! Let's just double-check the syzkaller configuration to see if it's typically enabled. It usually is. But, assuming it *is* disabled...
If `CONFIG_QUOTA` is off, then `dev` is at offset 1056. `vfs_inode` is then at 1064. Thus, `i_sb` would reside at `1064 + 40 = 1104`. Then `1104 - 768 = 336`. And then `336 / 32 = 10.5`. This means `i_sb` would sit at offset 16 of `slot[10]`. Then offset 16 of `dtslot` is the same as offset 14 of `name`. Offset 14 of `name` is index 7. Index 7 of "ge_percpu" is 'p'. Then index 8 is 'u'. Then index 9 is out of bounds; it's zero! That means the string is "pu\0\0", and not "rcpu", as expected.
But wait, what if the first chunk isn't 11 characters long? If the first slot is `dtslot` (instead of `ldtentry`), then it takes 15 characters! When could the first slot be `dtslot`? Never, it's always either `ldtentry` or `idtentry`.
Let me think… the `dtInsertEntry` function says:
```c
/* write head/only segment */
if (p->header.flag & BT_LEAF) {
lh = (struct ldtentry *) h;
```
So, when it writes the head segment, it's an `ldtentry`. What if `p->header.flag` doesn't contain `BT_LEAF`? If it doesn't, then it is an `idtentry`. Okay, time to check `idtentry`.
|
| 67/2 |
2026/05/26 00:12 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dtree.h IncludeLines:true Name:idtentry]
Results: map[SourceCode: 49: /*
50: * internal node entry head/only segment
51: */
52: struct idtentry {
53: pxd_t xd; /* 8: child extent descriptor */
54:
55: s8 next; /* 1: */
56: u8 namlen; /* 1: */
57: __le16 name[11]; /* 22: 2-byte aligned */
58: }; /* (32) */
SourceFile:fs/jfs/jfs_dtree.h]
|
| 68/2 |
2026/05/26 00:12 |
llm |
expert |
0m
Model:
Tokens:
input: 69694
output: 44
thoughts: 6728
Thoughts: **Analyzing JFS Corruption: A Deep Dive into Wild Pointers and Data Structures**
Okay, so I'm on the trail of a particularly nasty JFS bug, probably triggered by file system corruption. I'm focusing on how the `openat` call, when given a crafted filename like "cpuacct.usage_percpu", could overwrite crucial data. Specifically, I'm trying to figure out how a wild pointer, which contains the string "rcpu", is being written to memory and, more importantly, where it's ending up.
The trace suggests that the `name` field of an `idtentry` or `dtslot` is the likely target. I've considered that the corruption stems from how the directory tree is structured, specifically in its `_dtroot` and associated slots. I've gone back and forth between whether we're dealing with a leaf node or a legacy format entry. If a "leaf" entry is being written, then we're dealing with an `idtentry` where the name starts at offset 10, otherwise, we're likely in a `dtslot` where `name` starts at offset 2.
The key is that the corruption is writing the last four characters of the filename, "rcpu", into memory. I've tracked the string "cpuacct.usage_percpu" and broken it into "chunks" corresponding to writes to these directory entries. If the first 11 bytes are taken by an `idtentry`, the next 15 are written to the `dtslot`.
The important structure I'm following is the `dtslot`. I've determined that the `i_sb` field of the `inode` (which contains crucial filesystem metadata) is at offset 40 bytes. This means when we see the "rcpu" string, if that is the overwrite target, the bytes representing `i_sb` must be written at a specific location. Based on some calculations, if the `i_sb` field is getting written to, it's overwriting data in a `dtslot`. Since the `name` field starts at offset 2 in the `dtslot`, and the bytes "rcpu" are at the 16th, 17th, 18th, and 19th position in the filename "cpuacct.usage_percpu", which corresponds to the 6th, 7th, 8th and 9th bytes in the second chunk of 9 bytes, these correspond to the location where `i_sb` must be written.
The trouble is, the chunks of bytes are being written at the wrong location: If `fsi` is set to 11, then the `dtslot` is written at offset 1120. `i_sb` is at offset 40 in the `inode`, and there is no alignment. With some additional calculations, the address of the `dtslot` should be: `768 + 11*32`. However, it does not match where the wild pointer is pointing.
I've carefully double-checked all the relevant structures: `jfs_inode_info`, `inode`, `dtslot`, `ldtentry`, and even the union that contains directory entries, ensuring I've accounted for padding, alignment, and any potential configuration-dependent changes. I had to look at `codesearch-struct-layout` to ensure the offsets were correct. The question I'm trying to answer is if `i_sb` is at the correct location, which is at offset 40 of the `inode`. I also considered what happens when debug configurations are enabled or disabled. This makes it challenging, as the kernel is built with several debug options. However, even with all configurations enabled and disabled, `i_sb` is always at offset 40.
Ultimately, the calculations point to an inconsistency. The offset of `i_sb` based on the presumed slot and the structure layout doesn't align with where the corrupted "rcpu" string appears to be written. The mismatch must be in my assumptions about the write locations, and the format being used. There must be a subtle detail in how `dtInsertEntry` handles different directory formats, and the length of the string passed into it that I'm missing. The key may be in whether it's an `idtentry` or a `dtslot`, or if legacy format is used in some case.
|
| 69/2 |
2026/05/26 00:13 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:fs/jfs/jfs_dtree.h IncludeLines:true Name:DO_INDEX]
Results: map[SourceCode: SourceFile:]
|
| 70/2 |
2026/05/26 00:13 |
llm |
expert |
0m
Model:
Tokens:
input: 77440
output: 19
thoughts: 10
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Initial Assessment: DO_INDEX Search Required**
Alright, I see the trigger: `DO_INDEX`. My initial thought is a straightforward one – we're diving into an indexing operation, likely a database index, a search index for information retrieval, or possibly an indexing methodology related to another system. My experience in this area means I immediately begin to assess the potential context based on that single keyword. What kind of data are we dealing with? What system is involved? Is this a rebuild, an update, or a new implementation? I need more information, but `DO_INDEX` is the clear starting point for my investigation. My expertise tells me there's an indexing process to be addressed. Now, I need to understand *how* it is being undertaken.
|
| 71/2 |
2026/05/26 00:13 |
tool |
grepper |
0m
Args: map[Expression:#define DO_INDEX]
Results: map[Output:fs/jfs/jfs_dtree.h=72=struct ldtentry {
--
fs/jfs/jfs_dtree.h-90- */
fs/jfs/jfs_dtree.h:91:#define DO_INDEX(INODE) (JFS_SBI((INODE)->i_sb)->mntflag & JFS_DIR_INDEX)
fs/jfs/jfs_dtree.h-92-
]
|
| 72/2 |
2026/05/26 00:13 |
llm |
expert |
0m
Model:
Tokens:
input: 77772
output: 43
thoughts: 1227
Thoughts: **JFS Bug Analysis: A Deep Dive into the Reproducer**
Okay, here's what's clicking in my head. This `DO_INDEX` flag is key, and it's tied to the `JFS_DIR_INDEX` mount option. The syzkaller reproducer didn't specify that option, or it might be disabled by default. Let's check those mount options. It looks like the options passed are basically empty, which means `dir_index` is *not* enabled. Thus, `DO_INDEX` is false, and this is important.
Now, if `DO_INDEX` is false, `data.leaf.ip` will be NULL. The code then calculates `len` as the minimum of `klen` and `DTLHDRDATALEN_LEGACY`. `DTLHDRDATALEN_LEGACY` is only 13 bytes! The string we're dealing with, "cpuacct.usage_percpu", is 20 characters long. This means our first chunk will take 13 characters! So, we get "cpuacct.usage". The remaining 7 characters "_percpu" form the second chunk.
The second chunk is written to `dtslot`. Now, `dtslot.name` starts at offset 2. And, here's where it gets interesting: if `i_sb` is at offset 8 in this slot, the code overwrites it with characters from offset 6 of the original string. Offset 6 of the original string that's being written contains the 4th character of the second chunk: "_percpu". Specifically, it's 'r', 'c', 'p', 'u' - exactly! This explains the wild pointer!
Aha! `i_sb` is located at offset 8 of `slot[11]`! And, this is *exactly* a buffer overflow in `dtInsertEntry` where we are corrupting an inline directory! This corrupted inline directory has a `freelist` that's pointing to 11. `slot[11]` is *out of bounds* for a `dtroot_t`, which has slots from 0 to 8! So, writing to `slot[11]` is overwriting something beyond the bounds of the valid slots! It's overwriting the `vfs_inode->i_sb` pointer! And then we get the crash when `inode_set_ctime_current(dip)` is called, because it dereferences a corrupted `dip->i_sb`.
Is this exploitable? Hell yes! This is a classic buffer overflow scenario. The attacker controls the `freelist` index in the crafted JFS image. They can set the `freelist` to any value up to 127 because the `freelist` is an `s8` type. This means they can write the filename (which they control) to any offset within `127 * 32 = 4064` bytes after `_dtroot`. `_dtroot` itself is at offset 768 in the `jfs_inode_info` structure.
This means they can overwrite anything from 768 to `768 + 4064 = 4832` bytes of the `jfs_inode_info`. Wait... `jfs_inode_info` is allocated from the slab cache. And, is `vfs_inode` within `jfs_inode_info`? Yes! Can they write past the `jfs_inode_info`? The size of `jfs_inode_info` is 2368 bytes. The attacker can overwrite up to 4832 bytes! They can overwrite *adjacent* objects in the slab cache! That's devastating!
They can overwrite *`vfs_inode`* fields! Fields like `i_op`, `i_fop`, `i_sb` and others. These fields contain function pointers or pointers to structures with function pointers.
This is a trivial Local Privilege Escalation (LPE) if the attacker can mount a crafted JFS image. However, can an unprivileged user mount a JFS image? Usually, you need `CAP_SYS_ADMIN` in the initial user namespace. But, user namespaces! Unprivileged users can create a new user namespace, get `CAP_SYS_ADMIN` in that namespace, and mount some filesystems. BUT! Does JFS have the `FS_USERNS_MOUNT` flag? I need to verify!
|
| 73/2 |
2026/05/26 00:14 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/super.c IncludeLines:true Name:jfs_fs_type]
Results: map[SourceCode: 927: static struct file_system_type jfs_fs_type = {
928: .owner = THIS_MODULE,
929: .name = "jfs",
930: .kill_sb = kill_block_super,
931: .fs_flags = FS_REQUIRES_DEV,
932: .init_fs_context = jfs_init_fs_context,
933: .parameters = jfs_param_spec,
934: };
SourceFile:fs/jfs/super.c]
|
| 74/2 |
2026/05/26 00:14 |
llm |
expert |
0m
Model:
Tokens:
input: 80197
output: 44
thoughts: 2877
Thoughts: **Analysis of the JFS Inline Directory Vulnerability**
Okay, so here's the breakdown of this JFS bug, from my perspective. `jfs_fs_type` mandates `FS_REQUIRES_DEV` but *doesn't* allow `FS_USERNS_MOUNT`, immediately ruling out unprivileged user namespace exploitation. It definitely requires `CAP_SYS_ADMIN` in the initial namespace to mount a JFS image. However, the "Aha!" moment came with the realization of the malicious filesystem trigger: an unprivileged user can potentially trigger this via an auto-mounted malicious JFS image from a USB drive.
Therefore this is indeed a *Malicious Filesystem Trigger* and a *Peripheral Trigger* because of USB devices. And also clearly a Denial of Service leading to a kernel crash, but it goes further. It is exploitable because it's a buffer overflow capable of overwriting function pointers within the `struct inode` or adjacent slab objects!
The core of the issue lies within the `dtInsertEntry` function. Specifically, there's a critical lack of bounds checking on `fsi`, the index into the directory slot array. While a `dtpage_t` has 128 slots, a `dtroot_t` (which is being used inline) only has 9 slots. A crafted image can corrupt `freelist` and `freecnt` such that a large `fsi` is written to. This means that a write can occur *past* the boundaries of `dtroot_t`, leading to an out-of-bounds write. The kernel is using this corrupted free list to write to a location that is outside the range of a smaller object, but is inside the range of a larger object.
Normal directory growth via operations like `mkdir` won't trigger this because the kernel correctly handles inline directory conversion to a tree structure (via `dtSplitUp`). The only pathway to corrupt the `freelist` is through mounting a specially crafted JFS image.
To summarize the critical dimensions:
* **Exploitable: Yes**. Out-of-bounds write controlled by the attacker (filename) at an attacker-controlled offset (via `freelist`), potentially overwriting `i_op`, `i_fop`, or even adjacent slab objects.
* **Denial of Service: Yes**. Kernel crash.
* **Unprivileged Process: No**. `CAP_SYS_ADMIN` required to mount.
* **User Namespace: No**. `FS_USERNS_MOUNT` is not allowed.
* **Peripheral Trigger: Yes**. USB auto-mount is a key factor.
* **Malicious Filesystem Trigger: Yes**. This is the core exploit method.
The trigger mechanism is quite precise. The call stack is: Mount a crafted JFS image, then a call to `openat(..., O_CREAT)` which calls `jfs_create` which leads to `dtInsert` and, finally, `dtInsertEntry`. `dtInsertEntry` uses the corrupt `freelist`, writes the filename out-of-bounds, corrupting `i_sb` (the super block). `inode_set_ctime_current` then dereferences `i_sb` and crashes.
Looking at the precise memory layout (and double-checking the calculations, of course):
* Filename: "cpuacct.usage\_percpu" (20 characters)
* The overflow overwrites bytes at the `i_sb` offset (1128) of `jfs_inode_info`.
* After the calculation, the overwrite occurs at the address `0x0075007000630072`. This perfectly explains the wild pointer in the crash report! This is a 100% confirmation of the findings.
Crucially, it is not just `O_CREAT` that triggers it. *Any* operation adding an entry to a directory -- `mkdir`, `link`, `symlink`, `mknod`, or `rename` -- all these will work, *if* the attacker has write access (easily granted via control of the filesystem image) and can mount it.
Importantly, this is not triggered if the corrupt image is just present; the image *must* be mounted for the filesystem parsing to be done.
The vulnerability stems from the kernel's lack of checks when writing to the inline `dtroot_t`, leading to a very well defined out of bounds write.
The key to exploitability lies in *where* the write occurs. The code overwrites bytes into the `dtslot` struct, starting at a field called `name`, which is meant to store a filename. That `name` is written to `slot[11]`.
|
| 75/2 |
2026/05/26 00:14 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_unicode.c IncludeLines:true Name:get_UCSname]
Results: map[SourceCode: 96: /*
97: * NAME: get_UCSname()
98: *
99: * FUNCTION: Allocate and translate to unicode string
100: *
101: */
102: int get_UCSname(struct component_name * uniName, struct dentry *dentry)
103: {
104: struct nls_table *nls_tab = JFS_SBI(dentry->d_sb)->nls_tab;
105: int length = dentry->d_name.len;
106:
107: if (length > JFS_NAME_MAX)
108: return -ENAMETOOLONG;
109:
110: uniName->name =
111: kmalloc_array(length + 1, sizeof(wchar_t), GFP_NOFS);
112:
113: if (uniName->name == NULL)
114: return -ENOMEM;
115:
116: uniName->namlen = jfs_strtoUCS(uniName->name, dentry->d_name.name,
117: length, nls_tab);
118:
119: if (uniName->namlen < 0) {
120: kfree(uniName->name);
121: return uniName->namlen;
122: }
123:
124: return 0;
125: }
SourceFile:fs/jfs/jfs_unicode.c]
|
| 76/2 |
2026/05/26 00:14 |
llm |
expert |
0m
Model:
Tokens:
input: 84597
output: 44
thoughts: 262
Thoughts: **Analyzing the JFS String Conversion**
Okay, so `jfs_strtoUCS` is the function that handles string conversion, got it. Now, if `nls_tab` is NULL, which it will be by default if no `iocharset` is explicitly provided, it's just going to zero-extend each byte of the input string, essentially doing a simple byte-to-wide character conversion.
```c
if (nls_tab) {
...
} else {
for (i = 0; i < len; i++)
to[i] = (wchar_t) from[i];
}
```
That means, an attacker exploiting a vulnerability here would be limited to crafting pointers where every odd byte is zero, like `XX 00 YY 00 ZZ 00 WW 00`. That's a definite restriction on their ability to forge arbitrary memory addresses. But, wait... could they specify an `iocharset` mount option? If they could, then the `nls_tab` wouldn't be NULL and different code would run.
Since they provide the filesystem image, they *shouldn't* be able to specify mount options directly (unless they mount it themselves, which they can't according to the established constraints). However, what if this image is auto-mounted by something like `udisks2`? That *could* use default mount options, potentially including `iocharset`. This is interesting; I need to look into whether the attacker has control over the mount parameters.
This brings up another question. Can the attacker somehow sneak an `iocharset` option into the JFS superblock itself? I'd better check the JFS superblock structure to see if there's an `iocharset` field. I need to know if the superblock allows this, or if any other metadata could influence the `iocharset`. That's the next step.
|
| 77/2 |
2026/05/26 00:14 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_superblock.h IncludeLines:true Name:jfs_superblock]
Results: map[SourceCode: 19: /*
20: * aggregate superblock
21: *
22: * The name superblock is too close to super_block, so the name has been
23: * changed to jfs_superblock. The utilities are still using the old name.
24: */
25: struct jfs_superblock {
26: char s_magic[4]; /* 4: magic number */
27: __le32 s_version; /* 4: version number */
28:
29: __le64 s_size; /* 8: aggregate size in hardware/LVM blocks;
30: * VFS: number of blocks
31: */
32: __le32 s_bsize; /* 4: aggregate block size in bytes;
33: * VFS: fragment size
34: */
35: __le16 s_l2bsize; /* 2: log2 of s_bsize */
36: __le16 s_l2bfactor; /* 2: log2(s_bsize/hardware block size) */
37: __le32 s_pbsize; /* 4: hardware/LVM block size in bytes */
38: __le16 s_l2pbsize; /* 2: log2 of s_pbsize */
39: __le16 pad; /* 2: padding necessary for alignment */
40:
41: __le32 s_agsize; /* 4: allocation group size in aggr. blocks */
42:
43: __le32 s_flag; /* 4: aggregate attributes:
44: * see jfs_filsys.h
45: */
46: __le32 s_state; /* 4: mount/unmount/recovery state:
47: * see jfs_filsys.h
48: */
49: __le32 s_compress; /* 4: > 0 if data compression */
50:
51: pxd_t s_ait2; /* 8: first extent of secondary
52: * aggregate inode table
53: */
54:
55: pxd_t s_aim2; /* 8: first extent of secondary
56: * aggregate inode map
57: */
58: __le32 s_logdev; /* 4: device address of log */
59: __le32 s_logserial; /* 4: log serial number at aggregate mount */
60: pxd_t s_logpxd; /* 8: inline log extent */
61:
62: pxd_t s_fsckpxd; /* 8: inline fsck work space extent */
63:
64: struct timestruc_t s_time; /* 8: time last updated */
65:
66: __le32 s_fsckloglen; /* 4: Number of filesystem blocks reserved for
67: * the fsck service log.
68: * N.B. These blocks are divided among the
69: * versions kept. This is not a per
70: * version size.
71: * N.B. These blocks are included in the
72: * length field of s_fsckpxd.
73: */
74: s8 s_fscklog; /* 1: which fsck service log is most recent
75: * 0 => no service log data yet
76: * 1 => the first one
77: * 2 => the 2nd one
78: */
79: char s_fpack[11]; /* 11: file system volume name
80: * N.B. This must be 11 bytes to
81: * conform with the OS/2 BootSector
82: * requirements
83: * Only used when s_version is 1
84: */
85:
86: /* extendfs() parameter under s_state & FM_EXTENDFS */
87: __le64 s_xsize; /* 8: extendfs s_size */
88: pxd_t s_xfsckpxd; /* 8: extendfs fsckpxd */
89: pxd_t s_xlogpxd; /* 8: extendfs logpxd */
90: uuid_t s_uuid; /* 16: 128-bit uuid for volume */
91: char s_label[16]; /* 16: volume label */
92: uuid_t s_loguuid; /* 16: 128-bit uuid for log device */
93:
94: };
SourceFile:fs/jfs/jfs_superblock.h]
|
| 78/2 |
2026/05/26 00:14 |
llm |
expert |
0m
Model:
Tokens:
input: 86642
output: 66
thoughts: 1902
Thoughts: **Exploitation of JFS Filesystem with `iocharset` Vulnerability**
Okay, so the lack of an `iocharset` in the superblock is the key here. It prevents an attacker from specifying the character set through the image, and if it's not defined, `nls_tab` is NULL. This means, I'm limited to writing pointers of the form `XX 00 YY 00 ZZ 00 WW 00`. The question is, can I actually leverage this limited write? The answer, surprisingly, is yes. Even though I can only control every other byte, I can overwrite crucial structures.
Initially, I thought about overwriting `i_op` with a user-space address, and I can do this! But I quickly realized that SMAP (Supervisor Mode Access Prevention) is going to thwart that plan by preventing the kernel from directly reading from user-space. Reading from a user-space `i_op` entry will cause a fault. My initial attempts to craft valid kernel addresses were also unsuccessful because of the `00` byte restriction, which means I can't construct addresses like `0xffffffff80000000`.
However, the vulnerability doesn't end there! I then realized I can overwrite `i_sb` with a user-space address, and SMAP would still prevent me from successfully reading the `i_sb->s_time_gran` fields, causing a crash. This is what caused the syzkaller crash!
More interesting is the ability to overwrite various other fields. I can overwrite `i_size`, even if I'm not writing any pointers. This means I can create an out-of-bounds read/write in a file. `i_size` is at offset 1168 bytes, which translates to slot[12] if I'm writing at 32-byte-aligned addresses. I can definitely overwrite `i_size` by writing to `slot[12]`.
I could also mess with `i_uid` or `i_gid`, but since I control the filesystem image, it doesn't give me much that I can't already control.
The most promising attack vector is adjacent objects in the slab cache. `jfs_inode_info` is allocated from `jfs_inode_cachep`, and I can potentially overwrite fields of the NEXT object. I can overwrite the `i_uid` (at offset 32), and since I control the slot index, I can strategically overwrite the next object. This means if I have the right alignment I could overwrite the `i_uid` of an *other* inode.
Even though I am still constrained with the `00` bytes, I can target adjacent inodes from different filesystems, like `ext4_inode_cache` or `proc_inode_cache`, which are sometimes merged. Overwriting the `i_uid` of a `/proc/self/uid_map` inode would be a significant privilege escalation!
Since I can set the *exact* slot index to overwrite `i_uid`, even with the `00` bytes restriction, this is an exploitable local privilege escalation. I can overwrite it with my own UID, then read/write files like `/etc/shadow`!
So, to summarize, this is definitely exploitable. It's a Local Privilege Escalation, and can cause a Denial of Service. It's triggered by a filesystem or peripheral event.
I will now call `set-results`.
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| 79/2 |
2026/05/26 00:15 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:true NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
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| 80/2 |
2026/05/26 00:15 |
llm |
expert |
0m
Model:
Tokens:
input: 89421
output: 736
thoughts: 663
Thoughts: **Finalizing the Analysis**
Okay, the results are in. Time to solidify this into the final response.
The core of the issue boils down to an out-of-bounds write in the `dtInsertEntry` function, specifically within the JFS filesystem. The vulnerability manifests during the creation of a new file or directory, where `jfs_create` calls `dtInsert`, which ultimately calls `dtInsertEntry` to add the new directory entry.
The crux of the problem lies in how inline directories are handled. If the parent directory is an inline directory—stored within the inode structure itself—`dtInsertEntry` attempts to allocate a free slot from the directory's freelist, `p->header.freelist`. The critical oversight is the lack of bounds checking on this freelist index. This creates a gaping hole.
A carefully crafted JFS image, mounted by the system, could include a corrupted inline directory with a `freelist` index that points *outside* the valid boundaries of the inline directory, which is defined by the `dtroot_t` structure and has a limited number of slots. This is a classic buffer overflow scenario.
When this out-of-bounds index is used, `dtInsertEntry` will write the new file's name into memory locations adjacent to the inline directory data within the `jfs_inode_info` structure, or even beyond the structure's limits into neighboring slab objects. In the crash report evidence, we observed the crafted index corrupting the filename ("cpuacct.usage_percpu") and overwriting the `vfs_inode->i_sb` pointer. The string, in UTF-16LE, ended up causing the substring "rcpu" (or more precisely, `72 00 63 00 70 00 75 00` in hex) to overwrite the `i_sb` pointer. The ensuing attempt to dereference the pointer by `inode_set_ctime_current` during a later operation resulted in a General Protection Fault when trying to access `inode->i_sb->s_time_gran`.
**Exploitability: High**
This is a highly exploitable buffer overflow. The attacker has significant control:
* **Offset:** The attacker fully controls the offset, since the `freelist` index dictates where the write occurs.
* **Data:** The filename itself is under the attacker's control, giving them control of the data being written.
Although the data is converted to UTF-16LE, meaning every odd byte is zero if no NLS table is used, this doesn't limit the damage. An attacker can still overwrite critical fields in adjacent inodes within the slab cache, if one is used. This has the potential to grant ownership to a malicious actor on sensitive files like `/etc/shadow` that belong to other filesystems. The attacker could also overwrite fields like `i_size` to facilitate out-of-bounds reads/writes.
**Accessibility: Limited, but Present**
JFS doesn't support unprivileged mounts. Users can't directly mount a crafted JFS image in a user namespace. So standard vulnerability testing within a user namespace won't apply to this problem.
However, the attack is still accessible if the system is configured to auto-mount external media, like USB drives, which is very common on desktop environments using packages such as `udisks2`. This bug can be triggered via Malicious Filesystem and Peripheral triggers.
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| 81/1 |
2026/05/26 00:15 |
action |
format-explanation |
0m
Results: map[Explanation:**Bug Analysis:**
The crash is caused by an out-of-bounds write in the JFS filesystem's directory
entry insertion code (`dtInsertEntry`).
When a new file is created in a JFS directory, `jfs_create` calls `dtInsert`,
which then calls `dtInsertEntry` to add the new entry to the directory. If the
parent directory is an inline directory (its data is stored directly within the
inode's `jfs_inode_info` structure), `dtInsertEntry` allocates a free slot using
the directory's internal freelist (`p->header.freelist`).
However, there is no bounds checking on the `freelist` index. If a crafted JFS
image is mounted, an attacker can supply a corrupted inline directory with a
`freelist` index that points outside the bounds of the inline directory array
(`dtroot_t`, which only has 9 slots). Because the inline directory is embedded
within the `jfs_inode_info` structure, an out-of-bounds slot index causes
`dtInsertEntry` to write the new file's name into adjacent fields of the
`jfs_inode_info` structure, or even past the end of the structure into adjacent
slab objects.
In the provided crash report, the `freelist` index was crafted such that the
filename (`cpuacct.usage_percpu`) was written over the `vfs_inode->i_sb`
pointer. The filename is converted to UTF-16LE, and the substring "rcpu" (which
is `72 00 63 00 70 00 75 00` in hex) overwrote the `i_sb` pointer. When
`inode_set_ctime_current` subsequently tried to access
`inode->i_sb->s_time_gran`, it dereferenced this wild pointer
(`0x0075007000630812`), causing a General Protection Fault.
**Security Impact:**
* **Exploitable:** Yes. This is a highly exploitable buffer overflow. An
attacker controls both the offset (via the `freelist` index) and the data (via
the filename). Although the data is converted to UTF-16LE (meaning every odd
byte is `0x00` if no NLS table is used), the attacker can still overwrite
critical fields. For example, they can overwrite the `i_uid` or `i_gid` of
adjacent inodes in the slab cache (since slab caches are often merged),
potentially granting themselves ownership of sensitive files belonging to other
filesystems. They could also overwrite `i_size` to cause out-of-bounds
reads/writes, or corrupt function pointers if they can bypass SMAP.
* **Denial of Service:** Yes. Triggering the bug easily leads to a kernel
panic/crash.
* **Accessible From Unprivileged Processes / User Namespaces:** No. The JFS
filesystem does not have the `FS_USERNS_MOUNT` flag. Therefore, an unprivileged
user cannot mount a crafted JFS image directly, not even within a user
namespace. It requires `CAP_SYS_ADMIN` in the initial namespace.
* **Malicious Filesystem / Peripheral Trigger:** Yes. The bug can be triggered
if the system is configured to auto-mount external media (e.g., plugging in a
USB drive with a crafted JFS image on a Linux desktop environment running
`udisks2`).]
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