| 0/0 |
2026/01/27 18:44 |
flow |
patching |
27m
Results: map[PatchDescription:jfs: fix array-index-out-of-bounds in dbFindLeaf
Syzkaller reported the following UBSAN array-index-out-of-bounds issue in
dbFindLeaf:
UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:2976:16
index 1365 is out of range for type 's8[1365]' (aka 'signed char[1365]')
...
dbFindLeaf+0x308/0x520 fs/jfs/jfs_dmap.c:2976
dbFindCtl+0x267/0x520 fs/jfs/jfs_dmap.c:1717
...
The function dbFindLeaf() iterates through the dmap tree to find a leaf
with sufficient free blocks. The code calculates an index `x + n` into
the `tp->dmt_stree` array. The bounds check `if (x + n > max_size)`
fails to catch the case where `x + n` equals `max_size`.
When `is_ctl` is true, `max_size` is set to `CTLTREESIZE` (1365). If
`x + n` becomes 1365, the check passes, and the code accesses
`tp->dmt_stree[1365]`, which is out of bounds. This can happen if
`tp->dmt_height` is corrupted (too large), causing the loop to descend
deeper than expected.
Fix this by using `>=` in the bounds check to ensure the index is within
the valid range [0, max_size - 1]. PatchDiff:diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cdfa699cd..18a7dc58f 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2971,7 +2971,7 @@ static int dbFindLeaf(dmtree_t *tp, int l2nb, int *leafidx, bool is_ctl)
/* sufficient free space found. move to the next
* level (or quit if this is the last level).
*/
- if (x + n > max_size)
+ if (x + n >= max_size)
return -ENOSPC;
if (l2nb <= tp->dmt_stree[x + n])
break;
]
|
| 1/1 |
2026/01/27 18:44 |
action |
base-commit-picker |
0m
Results: map[KernelCommit:v6.19-rc7 KernelRepo:git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git]
|
| 2/1 |
2026/01/27 18:44 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/5452af61ab2e1f5601403fe379188fc9d8a831af]
|
| 3/1 |
2026/01/27 18:44 |
action |
kernel-builder |
5m
Results: map[KernelObj:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/build/53ac19c90e186abedbf71cada4c0776d55521b7f]
|
| 4/1 |
2026/01/27 18:50 |
action |
crash-reproducer |
2m
Results: map[CrashReport:------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in /usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/5452af61ab2e1f5601403fe379188fc9d8a831af/fs/jfs/jfs_dmap.c:2976:16
index 1365 is out of range for type 's8[1365]' (aka 'signed char[1365]')
CPU: 1 UID: 0 PID: 6199 Comm: syz-executor257 Not tainted syzkaller #1 PREEMPT_{RT,(full)}
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x10e/0x190 lib/dump_stack.c:120
ubsan_epilogue lib/ubsan.c:233 [inline]
__ubsan_handle_out_of_bounds+0x115/0x140 lib/ubsan.c:455
dbFindLeaf+0x308/0x520 fs/jfs/jfs_dmap.c:2976
dbFindCtl+0x267/0x520 fs/jfs/jfs_dmap.c:1717
dbAllocAny fs/jfs/jfs_dmap.c:1527 [inline]
dbAlloc+0x5fd/0xba0 fs/jfs/jfs_dmap.c:878
diNewIAG fs/jfs/jfs_imap.c:2510 [inline]
diAllocExt fs/jfs/jfs_imap.c:1905 [inline]
diAllocAG+0xcf0/0x1db0 fs/jfs/jfs_imap.c:1669
diAlloc+0x1d4/0x1670 fs/jfs/jfs_imap.c:1590
ialloc+0x8c/0x8f0 fs/jfs/jfs_inode.c:56
jfs_mkdir+0x193/0xa70 fs/jfs/namei.c:225
vfs_mkdir+0x530/0x5d0 fs/namei.c:5139
do_mkdirat+0x27a/0x4b0 fs/namei.c:5173
__do_sys_mkdir fs/namei.c:5200 [inline]
__se_sys_mkdir fs/namei.c:5198 [inline]
__x64_sys_mkdir+0x6c/0x80 fs/namei.c:5198
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe8/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc490daf897
Code: 1f 40 00 48 89 f2 b9 00 01 00 00 48 89 fe bf 9c ff ff ff e9 7b 37 03 00 66 2e 0f 1f 84 00 00 00 00 00 90 b8 53 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d0 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fc490d51038 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 0000200000000200 RCX: 00007fc490daf897
RDX: 0000000002b1247d RSI: 00000000000001ff RDI: 00002000000002c0
RBP: 0000000000000000 R08: 00000000000000fc R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 00002000000002c0
R13: 00007fc490d510d0 R14: 0000000000000000 R15: 0000000000000000
</TASK>
---[ end trace ]---
]
|
| 5/1 |
2026/01/27 18:53 |
action |
codesearch-prepare |
2m
Results: map[Index:codesearch-index]
|
| 6/1 |
2026/01/27 18:55 |
agent |
debugger |
2m
Model:
Instruction:
You are an experienced Linux kernel developer tasked with debugging a kernel crash root cause.
You need to provide a detailed explanation of the root cause for another developer to be
able to write a fix for the bug based on your explanation.
Your final reply must contain only the explanation.
Call some codesearch tools first.
Prefer calling several tools at the same time to save round-trips.
Prompt:
The crash is:
------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in /usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/5452af61ab2e1f5601403fe379188fc9d8a831af/fs/jfs/jfs_dmap.c:2976:16
index 1365 is out of range for type 's8[1365]' (aka 'signed char[1365]')
CPU: 1 UID: 0 PID: 6199 Comm: syz-executor257 Not tainted syzkaller #1 PREEMPT_{RT,(full)}
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x10e/0x190 lib/dump_stack.c:120
ubsan_epilogue lib/ubsan.c:233 [inline]
__ubsan_handle_out_of_bounds+0x115/0x140 lib/ubsan.c:455
dbFindLeaf+0x308/0x520 fs/jfs/jfs_dmap.c:2976
dbFindCtl+0x267/0x520 fs/jfs/jfs_dmap.c:1717
dbAllocAny fs/jfs/jfs_dmap.c:1527 [inline]
dbAlloc+0x5fd/0xba0 fs/jfs/jfs_dmap.c:878
diNewIAG fs/jfs/jfs_imap.c:2510 [inline]
diAllocExt fs/jfs/jfs_imap.c:1905 [inline]
diAllocAG+0xcf0/0x1db0 fs/jfs/jfs_imap.c:1669
diAlloc+0x1d4/0x1670 fs/jfs/jfs_imap.c:1590
ialloc+0x8c/0x8f0 fs/jfs/jfs_inode.c:56
jfs_mkdir+0x193/0xa70 fs/jfs/namei.c:225
vfs_mkdir+0x530/0x5d0 fs/namei.c:5139
do_mkdirat+0x27a/0x4b0 fs/namei.c:5173
__do_sys_mkdir fs/namei.c:5200 [inline]
__se_sys_mkdir fs/namei.c:5198 [inline]
__x64_sys_mkdir+0x6c/0x80 fs/namei.c:5198
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe8/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc490daf897
Code: 1f 40 00 48 89 f2 b9 00 01 00 00 48 89 fe bf 9c ff ff ff e9 7b 37 03 00 66 2e 0f 1f 84 00 00 00 00 00 90 b8 53 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d0 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fc490d51038 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 0000200000000200 RCX: 00007fc490daf897
RDX: 0000000002b1247d RSI: 00000000000001ff RDI: 00002000000002c0
RBP: 0000000000000000 R08: 00000000000000fc R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 00002000000002c0
R13: 00007fc490d510d0 R14: 0000000000000000 R15: 0000000000000000
</TASK>
---[ end trace ]---
Reply: The root cause of this crash is an off-by-one error in the bounds check within the `dbFindLeaf` function in `fs/jfs/jfs_dmap.c`.
The function `dbFindLeaf` iterates through the levels of a dmap tree to find a leaf with sufficient free blocks. The number of iterations is determined by `tp->dmt_height`, which is read from the filesystem image (disk). The crash occurs when `tp->dmt_height` is corrupted (too large), causing the loop to descend deeper than the defined tree structure allows, resulting in the calculated index `x + n` exceeding the valid range of the `tp->dmt_stree` array.
Specifically:
1. The array `tp->dmt_stree` has a size of `CTLTREESIZE` (1365) when `is_ctl` is true (which is the case in the stack trace, called from `dbFindCtl`). The valid indices are `0` to `1364`.
2. The code includes a bounds check at line 2974: `if (x + n > max_size)`.
3. `max_size` is set to `CTLTREESIZE` (1365).
4. When `x + n` reaches `1365`, the condition `1365 > 1365` evaluates to false, allowing execution to proceed.
5. The code then attempts to access `tp->dmt_stree[1365]` at line 2976, triggering the UBSAN array-index-out-of-bounds error.
The bounds check should use `>=` instead of `>` to correctly handle the case where the index equals the array size.
**Fix:**
Change the bounds check in `fs/jfs/jfs_dmap.c` from:
```c
if (x + n > max_size)
```
to:
```c
if (x + n >= max_size)
```
|
| 7/2 |
2026/01/27 18:55 |
llm |
debugger |
0m
Model:
Tokens:
input: 3409
output: 75
thoughts: 349
Thoughts: **Debugging a JFS Array Index Out-of-Bounds Error**
Okay, so I'm getting a frustrating `array-index-out-of-bounds` error, specifically in `fs/jfs/jfs_dmap.c:2976`. The error details are pretty clear – index `1365` is exceeding the bounds of an array of type `s8[1365]`. This immediately tells me there's an off-by-one error lurking somewhere; valid indices range from 0 to 1364. The call stack gives me some breadcrumbs, it looks like `dbFindLeaf` is the function causing the problem, and that's being called from a chain that ultimately leads back to `jfs_mkdir`.
My initial thought is to zero in on that section of `jfs_dmap.c`, specifically around line 2976. I need to understand what array is being accessed at that point. The error message is very specific about the type, `s8[1365]`, which means it’s a character array or a signed 8-bit integer array. I'll use the `codesearch-definition-source` command to read the source code of `dbFindLeaf` and examine that part of the code, looking for the relevant array definition and how it's being indexed.
I'm already mentally breaking down the number `1365`. It feels like there might be some block size or alignment calculations involved. 1365 could be derived from $341 \times 4 + 1$ or $(1024 + 341)$ or similar. I'll be looking for any clues in the array's usage or surrounding calculations to see if any arithmetic errors could have caused this. Let's start with getting the source code of `dbFindLeaf` and begin.
|
| 8/2 |
2026/01/27 18:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeLines:true Name:dbFindLeaf]
Results: map[SourceCode:2924: /*
2925: * NAME: dbFindLeaf()
2926: *
2927: * FUNCTION: search a dmtree_t for sufficient free blocks, returning
2928: * the index of a leaf describing the free blocks if
2929: * sufficient free blocks are found.
2930: *
2931: * the search starts at the top of the dmtree_t tree and
2932: * proceeds down the tree to the leftmost leaf with sufficient
2933: * free space.
2934: *
2935: * PARAMETERS:
2936: * tp - pointer to the tree to be searched.
2937: * l2nb - log2 number of free blocks to search for.
2938: * leafidx - return pointer to be set to the index of the leaf
2939: * describing at least l2nb free blocks if sufficient
2940: * free blocks are found.
2941: * is_ctl - determines if the tree is of type ctl
2942: *
2943: * RETURN VALUES:
2944: * 0 - success
2945: * -ENOSPC - insufficient free blocks.
2946: */
2947: static int dbFindLeaf(dmtree_t *tp, int l2nb, int *leafidx, bool is_ctl)
2948: {
2949: int ti, n = 0, k, x = 0;
2950: int max_size, max_idx;
2951:
2952: max_size = is_ctl ? CTLTREESIZE : TREESIZE;
2953: max_idx = is_ctl ? LPERCTL : LPERDMAP;
2954:
2955: /* first check the root of the tree to see if there is
2956: * sufficient free space.
2957: */
2958: if (l2nb > tp->dmt_stree[ROOT])
2959: return -ENOSPC;
2960:
2961: /* sufficient free space available. now search down the tree
2962: * starting at the next level for the leftmost leaf that
2963: * describes sufficient free space.
2964: */
2965: for (k = le32_to_cpu(tp->dmt_height), ti = 1;
2966: k > 0; k--, ti = ((ti + n) << 2) + 1) {
2967: /* search the four nodes at this level, starting from
2968: * the left.
2969: */
2970: for (x = ti, n = 0; n < 4; n++) {
2971: /* sufficient free space found. move to the next
2972: * level (or quit if this is the last level).
2973: */
2974: if (x + n > max_size)
2975: return -ENOSPC;
2976: if (l2nb <= tp->dmt_stree[x + n])
2977: break;
2978: }
2979:
2980: /* better have found something since the higher
2981: * levels of the tree said it was here.
2982: */
2983: assert(n < 4);
2984: }
2985: if (le32_to_cpu(tp->dmt_leafidx) >= max_idx)
2986: return -ENOSPC;
2987:
2988: /* set the return to the leftmost leaf describing sufficient
2989: * free space.
2990: */
2991: *leafidx = x + n - le32_to_cpu(tp->dmt_leafidx);
2992:
2993: return (0);
2994: }
SourceFile:fs/jfs/jfs_dmap.c]
|
| 9/2 |
2026/01/27 18:55 |
tool |
codesearch-file-index |
0m
Args: map[SourceFile:fs/jfs/jfs_dmap.c]
Results: map[Entities:[map[Kind:function Name:blkstol2] map[Kind:function Name:cntlz] map[Kind:function Name:cnttz] map[Kind:function Name:dbAdjCtl] map[Kind:function Name:dbAdjTree] map[Kind:function Name:dbAlloc] map[Kind:function Name:dbAllocAG] map[Kind:function Name:dbAllocAny] map[Kind:function Name:dbAllocBits] map[Kind:function Name:dbAllocBottomUp] map[Kind:function Name:dbAllocCtl] map[Kind:function Name:dbAllocDmap] map[Kind:function Name:dbAllocDmapBU] map[Kind:function Name:dbAllocDmapLev] map[Kind:function Name:dbAllocNear] map[Kind:function Name:dbAllocNext] map[Kind:function Name:dbBackSplit] map[Kind:function Name:dbDiscardAG] map[Kind:function Name:dbExtend] map[Kind:function Name:dbExtendFS] map[Kind:function Name:dbFinalizeBmap] map[Kind:function Name:dbFindBits] map[Kind:function Name:dbFindCtl] map[Kind:function Name:dbFindLeaf] map[Kind:function Name:dbFree] map[Kind:function Name:dbFreeBits] map[Kind:function Name:dbFreeDmap] map[Kind:function Name:dbGetL2AGSize] map[Kind:function Name:dbInitDmap] map[Kind:function Name:dbInitDmapCtl] map[Kind:function Name:dbInitDmapTree] map[Kind:function Name:dbInitTree] map[Kind:function Name:dbJoin] map[Kind:function Name:dbMapFileSizeToMapSize] map[Kind:function Name:dbMaxBud] map[Kind:function Name:dbMount] map[Kind:function Name:dbNextAG] map[Kind:function Name:dbReAlloc] map[Kind:function Name:dbSplit] map[Kind:function Name:dbSync] map[Kind:function Name:dbUnmount] map[Kind:function Name:dbUpdatePMap]]]
|
| 10/2 |
2026/01/27 18:55 |
llm |
debugger |
0m
Model:
Tokens:
input: 5990
output: 35
thoughts: 169
Thoughts: **Debugging a JFS Index Out-of-Bounds Error**
Alright, let's break this down. The kernel's complaining about an out-of-bounds access at line 2976, specifically with the `if (l2nb <= tp->dmt_stree[x + n])` statement. The error message is clear: the index `1365` is out of bounds for an array of type `s8[1365]`. So, *that* tells me immediately that `tp->dmt_stree` has been incorrectly indexed.
The compiler is pretty straightforward here. The array itself is indeed `s8[1365]`.
Now, I need to understand what `dmtree_t` *is*. I'm going to track that down in the JFS file structure. I'll search the `fs/jfs/` directory for the definition of `dmtree_t`. Given that the error originates in `fs/jfs/`, I'd bet it is defined in either `jfs_dmap.h` or, perhaps, one of the files it includes. That should give me the structure and lead me to the root cause of the indexing problem. Time to dig into the header files.
|
| 11/2 |
2026/01/27 18:56 |
tool |
codesearch-find-references |
0m
Error:
Args: map[Name:dmtree_t SourceTreePrefix:fs/jfs/]
Results: map[References:<nil> TruncatedOutput:false]
|
| 12/2 |
2026/01/27 18:56 |
llm |
debugger |
0m
Model:
Tokens:
input: 6489
output: 23
thoughts: 64
Thoughts: **Investigating the Definition of `dmtree_t`**
Okay, so I need to figure out what `dmtree_t` actually *is*. My first instinct is that it's probably a `typedef`. Given the context, it's likely a structure specific to the JFS filesystem. Let's start with the obvious: I'll search for `typedef struct dmtree` (or variations thereof) in the JFS directory. Might as well be thorough and just `grep` the whole `fs/jfs/` directory for it.
Alternatively, maybe it's *not* a typedef, or perhaps the relevant struct definition doesn't use the `typedef` approach. To ensure I cover all bases, I should list all the files in `fs/jfs/` and visually scan for header files. That's usually the best place to start looking for definitions. Let's see what that turns up.
|
| 13/2 |
2026/01/27 18:56 |
tool |
codesearch-dir-index |
0m
Args:
Results: map[Files:[acl.c file.c inode.c ioctl.c jfs_acl.h jfs_btree.h jfs_debug.c jfs_debug.h jfs_dinode.h jfs_discard.c jfs_discard.h jfs_dmap.c jfs_dmap.h jfs_dtree.c jfs_dtree.h jfs_extent.c jfs_extent.h jfs_filsys.h jfs_imap.c jfs_imap.h jfs_incore.h jfs_inode.c jfs_inode.h jfs_lock.h jfs_logmgr.c jfs_logmgr.h jfs_metapage.c jfs_metapage.h jfs_mount.c jfs_superblock.h jfs_txnmgr.c jfs_txnmgr.h jfs_types.h jfs_umount.c jfs_unicode.c jfs_unicode.h jfs_xattr.h jfs_xtree.c jfs_xtree.h namei.c resize.c super.c symlink.c xattr.c] Subdirs:<nil>]
|
| 14/2 |
2026/01/27 18:56 |
llm |
debugger |
0m
Model:
Tokens:
input: 7186
output: 27
thoughts: 32
Thoughts: Here's my take on the thought process, as if it were my own:
**Initial Assessment: Locating the Relevant Code**
Alright, based on what I'm working on, `jfs_dmap.h` *feels* like the logical starting point. The name is pretty clear, and given my expertise with JFS and the underlying data structures, this seems like the place where the definitions related to the Direct Map, should be. I'll dive into `fs/jfs/jfs_dmap.h` and start there. Let's see what we've got.
|
| 15/2 |
2026/01/27 18:56 |
tool |
read-file |
0m
Args: map[File:fs/jfs/jfs_dmap.h]
Results: map[Contents:/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Copyright (C) International Business Machines Corp., 2000-2002
*/
#ifndef _H_JFS_DMAP
#define _H_JFS_DMAP
#include "jfs_txnmgr.h"
#define BMAPVERSION 1 /* version number */
#define TREESIZE (256+64+16+4+1) /* size of a dmap tree */
#define LEAFIND (64+16+4+1) /* index of 1st leaf of a dmap tree */
#define LPERDMAP 256 /* num leaves per dmap tree */
#define L2LPERDMAP 8 /* l2 number of leaves per dmap tree */
#define DBWORD 32 /* # of blks covered by a map word */
#define L2DBWORD 5 /* l2 # of blks covered by a mword */
#define BUDMIN L2DBWORD /* max free string in a map word */
#define BPERDMAP (LPERDMAP * DBWORD) /* num of blks per dmap */
#define L2BPERDMAP 13 /* l2 num of blks per dmap */
#define CTLTREESIZE (1024+256+64+16+4+1) /* size of a dmapctl tree */
#define CTLLEAFIND (256+64+16+4+1) /* idx of 1st leaf of a dmapctl tree */
#define LPERCTL 1024 /* num of leaves per dmapctl tree */
#define L2LPERCTL 10 /* l2 num of leaves per dmapctl tree */
#define ROOT 0 /* index of the root of a tree */
#define NOFREE ((s8) -1) /* no blocks free */
#define MAXAG 128 /* max number of allocation groups */
#define L2MAXAG 7 /* l2 max num of AG */
#define L2MINAGSZ 25 /* l2 of minimum AG size in bytes */
#define BMAPBLKNO 0 /* lblkno of bmap within the map */
/*
* maximum l2 number of disk blocks at the various dmapctl levels.
*/
#define L2MAXL0SIZE (L2BPERDMAP + 1 * L2LPERCTL)
#define L2MAXL1SIZE (L2BPERDMAP + 2 * L2LPERCTL)
#define L2MAXL2SIZE (L2BPERDMAP + 3 * L2LPERCTL)
/*
* maximum number of disk blocks at the various dmapctl levels.
*/
#define MAXL0SIZE ((s64)1 << L2MAXL0SIZE)
#define MAXL1SIZE ((s64)1 << L2MAXL1SIZE)
#define MAXL2SIZE ((s64)1 << L2MAXL2SIZE)
#define MAXMAPSIZE MAXL2SIZE /* maximum aggregate map size */
/*
* determine the maximum free string for four (lower level) nodes
* of the tree.
*/
static inline signed char TREEMAX(signed char *cp)
{
signed char tmp1, tmp2;
tmp1 = max(*(cp+2), *(cp+3));
tmp2 = max(*(cp), *(cp+1));
return max(tmp1, tmp2);
}
/*
* convert disk block number to the logical block number of the dmap
* describing the disk block. s is the log2(number of logical blocks per page)
*
* The calculation figures out how many logical pages are in front of the dmap.
* - the number of dmaps preceding it
* - the number of L0 pages preceding its L0 page
* - the number of L1 pages preceding its L1 page
* - 3 is added to account for the L2, L1, and L0 page for this dmap
* - 1 is added to account for the control page of the map.
*/
#define BLKTODMAP(b,s) \
((((b) >> 13) + ((b) >> 23) + ((b) >> 33) + 3 + 1) << (s))
/*
* convert disk block number to the logical block number of the LEVEL 0
* dmapctl describing the disk block. s is the log2(number of logical blocks
* per page)
*
* The calculation figures out how many logical pages are in front of the L0.
* - the number of dmap pages preceding it
* - the number of L0 pages preceding it
* - the number of L1 pages preceding its L1 page
* - 2 is added to account for the L2, and L1 page for this L0
* - 1 is added to account for the control page of the map.
*/
#define BLKTOL0(b,s) \
(((((b) >> 23) << 10) + ((b) >> 23) + ((b) >> 33) + 2 + 1) << (s))
/*
* convert disk block number to the logical block number of the LEVEL 1
* dmapctl describing the disk block. s is the log2(number of logical blocks
* per page)
*
* The calculation figures out how many logical pages are in front of the L1.
* - the number of dmap pages preceding it
* - the number of L0 pages preceding it
* - the number of L1 pages preceding it
* - 1 is added to account for the L2 page
* - 1 is added to account for the control page of the map.
*/
#define BLKTOL1(b,s) \
(((((b) >> 33) << 20) + (((b) >> 33) << 10) + ((b) >> 33) + 1 + 1) << (s))
/*
* convert disk block number to the logical block number of the dmapctl
* at the specified level which describes the disk block.
*/
#define BLKTOCTL(b,s,l) \
(((l) == 2) ? 1 : ((l) == 1) ? BLKTOL1((b),(s)) : BLKTOL0((b),(s)))
/*
* convert aggregate map size to the zero origin dmapctl level of the
* top dmapctl.
*/
#define BMAPSZTOLEV(size) \
(((size) <= MAXL0SIZE) ? 0 : ((size) <= MAXL1SIZE) ? 1 : 2)
/* convert disk block number to allocation group number.
*/
#define BLKTOAG(b,sbi) ((b) >> ((sbi)->bmap->db_agl2size))
/* convert allocation group number to starting disk block
* number.
*/
#define AGTOBLK(a,ip) \
((s64)(a) << (JFS_SBI((ip)->i_sb)->bmap->db_agl2size))
/*
* dmap summary tree
*
* dmaptree must be consistent with dmapctl.
*/
struct dmaptree {
__le32 nleafs; /* 4: number of tree leafs */
__le32 l2nleafs; /* 4: l2 number of tree leafs */
__le32 leafidx; /* 4: index of first tree leaf */
__le32 height; /* 4: height of the tree */
s8 budmin; /* 1: min l2 tree leaf value to combine */
s8 stree[TREESIZE]; /* TREESIZE: tree */
u8 pad[2]; /* 2: pad to word boundary */
}; /* - 360 - */
/*
* dmap page per 8K blocks bitmap
*/
struct dmap {
__le32 nblocks; /* 4: num blks covered by this dmap */
__le32 nfree; /* 4: num of free blks in this dmap */
__le64 start; /* 8: starting blkno for this dmap */
struct dmaptree tree; /* 360: dmap tree */
u8 pad[1672]; /* 1672: pad to 2048 bytes */
__le32 wmap[LPERDMAP]; /* 1024: bits of the working map */
__le32 pmap[LPERDMAP]; /* 1024: bits of the persistent map */
}; /* - 4096 - */
/*
* disk map control page per level.
*
* dmapctl must be consistent with dmaptree.
*/
struct dmapctl {
__le32 nleafs; /* 4: number of tree leafs */
__le32 l2nleafs; /* 4: l2 number of tree leafs */
__le32 leafidx; /* 4: index of the first tree leaf */
__le32 height; /* 4: height of tree */
s8 budmin; /* 1: minimum l2 tree leaf value */
s8 stree[CTLTREESIZE]; /* CTLTREESIZE: dmapctl tree */
u8 pad[2714]; /* 2714: pad to 4096 */
}; /* - 4096 - */
/*
* common definition for dmaptree within dmap and dmapctl
*/
typedef union dmtree {
struct dmaptree t1;
struct dmapctl t2;
} dmtree_t;
/* macros for accessing fields within dmtree */
#define dmt_nleafs t1.nleafs
#define dmt_l2nleafs t1.l2nleafs
#define dmt_leafidx t1.leafidx
#define dmt_height t1.height
#define dmt_budmin t1.budmin
#define dmt_stree t2.stree
/*
* on-disk aggregate disk allocation map descriptor.
*/
struct dbmap_disk {
__le64 dn_mapsize; /* 8: number of blocks in aggregate */
__le64 dn_nfree; /* 8: num free blks in aggregate map */
__le32 dn_l2nbperpage; /* 4: number of blks per page */
__le32 dn_numag; /* 4: total number of ags */
__le32 dn_maxlevel; /* 4: number of active ags */
__le32 dn_maxag; /* 4: max active alloc group number */
__le32 dn_agpref; /* 4: preferred alloc group (hint) */
__le32 dn_aglevel; /* 4: dmapctl level holding the AG */
__le32 dn_agheight; /* 4: height in dmapctl of the AG */
__le32 dn_agwidth; /* 4: width in dmapctl of the AG */
__le32 dn_agstart; /* 4: start tree index at AG height */
__le32 dn_agl2size; /* 4: l2 num of blks per alloc group */
__le64 dn_agfree[MAXAG];/* 8*MAXAG: per AG free count */
__le64 dn_agsize; /* 8: num of blks per alloc group */
s8 dn_maxfreebud; /* 1: max free buddy system */
u8 pad[3007]; /* 3007: pad to 4096 */
}; /* - 4096 - */
struct dbmap {
s64 dn_mapsize; /* number of blocks in aggregate */
s64 dn_nfree; /* num free blks in aggregate map */
int dn_l2nbperpage; /* number of blks per page */
int dn_numag; /* total number of ags */
int dn_maxlevel; /* number of active ags */
int dn_maxag; /* max active alloc group number */
int dn_agpref; /* preferred alloc group (hint) */
int dn_aglevel; /* dmapctl level holding the AG */
int dn_agheight; /* height in dmapctl of the AG */
int dn_agwidth; /* width in dmapctl of the AG */
int dn_agstart; /* start tree index at AG height */
int dn_agl2size; /* l2 num of blks per alloc group */
s64 dn_agfree[MAXAG]; /* per AG free count */
s64 dn_agsize; /* num of blks per alloc group */
signed char dn_maxfreebud; /* max free buddy system */
}; /* - 4096 - */
/*
* in-memory aggregate disk allocation map descriptor.
*/
struct bmap {
struct dbmap db_bmap; /* on-disk aggregate map descriptor */
struct inode *db_ipbmap; /* ptr to aggregate map incore inode */
struct mutex db_bmaplock; /* aggregate map lock */
atomic_t db_active[MAXAG]; /* count of active, open files in AG */
u32 *db_DBmap;
};
/* macros for accessing fields within in-memory aggregate map descriptor */
#define db_mapsize db_bmap.dn_mapsize
#define db_nfree db_bmap.dn_nfree
#define db_agfree db_bmap.dn_agfree
#define db_agsize db_bmap.dn_agsize
#define db_agl2size db_bmap.dn_agl2size
#define db_agwidth db_bmap.dn_agwidth
#define db_agheight db_bmap.dn_agheight
#define db_agstart db_bmap.dn_agstart
#define db_numag db_bmap.dn_numag
#define db_maxlevel db_bmap.dn_maxlevel
#define db_aglevel db_bmap.dn_aglevel
#define db_agpref db_bmap.dn_agpref
#define db_maxag db_bmap.dn_maxag
#define db_maxfreebud db_bmap.dn_maxfreebud
#define db_l2nbperpage db_bmap.dn_l2nbperpage
/*
* macros for various conversions needed by the allocators.
* blkstol2(), cntlz(), and cnttz() are operating system dependent functions.
*/
/* convert number of blocks to log2 number of blocks, rounding up to
* the next log2 value if blocks is not a l2 multiple.
*/
#define BLKSTOL2(d) (blkstol2(d))
/* convert number of leafs to log2 leaf value */
#define NLSTOL2BSZ(n) (31 - cntlz((n)) + BUDMIN)
/* convert leaf index to log2 leaf value */
#define LITOL2BSZ(n,m,b) ((((n) == 0) ? (m) : cnttz((n))) + (b))
/* convert a block number to a dmap control leaf index */
#define BLKTOCTLLEAF(b,m) \
(((b) & (((s64)1 << ((m) + L2LPERCTL)) - 1)) >> (m))
/* convert log2 leaf value to buddy size */
#define BUDSIZE(s,m) (1 << ((s) - (m)))
/*
* external references.
*/
extern int dbMount(struct inode *ipbmap);
extern int dbUnmount(struct inode *ipbmap, int mounterror);
extern int dbFree(struct inode *ipbmap, s64 blkno, s64 nblocks);
extern int dbUpdatePMap(struct inode *ipbmap,
int free, s64 blkno, s64 nblocks, struct tblock * tblk);
extern int dbNextAG(struct inode *ipbmap);
extern int dbAlloc(struct inode *ipbmap, s64 hint, s64 nblocks, s64 * results);
extern int dbReAlloc(struct inode *ipbmap,
s64 blkno, s64 nblocks, s64 addnblocks, s64 * results);
extern int dbSync(struct inode *ipbmap);
extern int dbAllocBottomUp(struct inode *ip, s64 blkno, s64 nblocks);
extern int dbExtendFS(struct inode *ipbmap, s64 blkno, s64 nblocks);
extern void dbFinalizeBmap(struct inode *ipbmap);
extern s64 dbMapFileSizeToMapSize(struct inode *ipbmap);
extern s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen);
#endif /* _H_JFS_DMAP */
]
|
| 16/2 |
2026/01/27 18:56 |
llm |
debugger |
0m
Model:
Tokens:
input: 11642
output: 45
thoughts: 4367
Thoughts: **Analysis of a Potential Out-of-Bounds Access in JFS dmap Tree Traversal**
Okay, so I'm looking at this C code related to the JFS file system and a potential error. The core of the problem seems to be an out-of-bounds access in a function called `dbFindLeaf`. This function is responsible for traversing a dmap tree, which is a quadtree structure used to manage free space on the disk.
The error message "index 1365 is out of range for type 's8[1365]'" is pretty clear. The code is trying to access an element beyond the allocated memory for an array of signed 8-bit characters (`s8`). The array `stree` is part of either the `dmaptree` or `dmapctl` structure, which are unions. The `dmapctl` structure uses a much larger tree than the `dmaptree` when we use the `CTLTREESIZE` macro, which is `1024 + 256 + 64 + 16 + 4 + 1 = 1365`. The array is being accessed via the `dmt_stree` macro which can expand to either `t1.stree` or `t2.stree`. This array is being accessed via `t2.stree` so the size should be 1365.
The function `dbFindLeaf` iterates through the tree levels. The critical part is the check `if (x + n > max_size)`. `x` and `n` are calculated within the loop, and they represent the index of the node we're currently looking at. The intention seems to be to prevent accessing an index beyond the allocated size (`max_size`) of the `stree` array. If `x + n` reaches the maximum array size 1365, it accesses the next memory location, which is out of range. The code's current check allows access when it is not strictly less than the maximum size, causing the OOB.
My analysis reveals that the core issue is an off-by-one error in the boundary check. The correct check should be `if (x + n >= max_size)`, which would catch the case where `x + n` equals `max_size`.
Looking more deeply, I need to understand how `x` and `n` are calculated within this loop. The loop uses a height variable obtained from `tp->dmt_height`. It iterates from the root of the tree down to the leaves. At each level, it searches through four nodes (n=0..3). The tree traversal itself uses quadtree indexing, where children of a node are computed using index arithmetic. The index is initialized and updated.
It also looks like it's possible for the tree traversal to reach an invalid index *even* if `dmt_height` is correct, because of errors in `stree` values. If a node in a higher level of the tree indicates we should go to an invalid index, we will go OOB. However, this is unlikely. This loop could be going beyond what's valid in memory by an off-by-one, even when `dmt_height` is correct.
The most likely culprit appears to be the height value being read from the dmap structure. It's possible that `tp->dmt_height` is incorrectly set to a value larger than the actual tree height, which then results in the loop running too many times and indexing out of bounds. The height should correspond to `CTLTREESIZE` or `TREESIZE`.
A correct fix is therefore to change the check in the inner loop to `>=`. We also need to validate height.
|
| 17/2 |
2026/01/27 18:57 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeLines:true Name:dbFindCtl]
Results: map[SourceCode:1653: /*
1654: * NAME: dbFindCtl()
1655: *
1656: * FUNCTION: starting at a specified dmap control page level and block
1657: * number, search down the dmap control levels for a range of
1658: * contiguous free blocks large enough to satisfy an allocation
1659: * request for the specified number of free blocks.
1660: *
1661: * if sufficient contiguous free blocks are found, this routine
1662: * returns the starting block number within a dmap page that
1663: * contains or starts a range of contiqious free blocks that
1664: * is sufficient in size.
1665: *
1666: * PARAMETERS:
1667: * bmp - pointer to bmap descriptor
1668: * level - starting dmap control page level.
1669: * l2nb - log2 number of contiguous free blocks desired.
1670: * *blkno - on entry, starting block number for conducting the search.
1671: * on successful return, the first block within a dmap page
1672: * that contains or starts a range of contiguous free blocks.
1673: *
1674: * RETURN VALUES:
1675: * 0 - success
1676: * -ENOSPC - insufficient disk resources
1677: * -EIO - i/o error
1678: *
1679: * serialization: IWRITE_LOCK(ipbmap) held on entry/exit;
1680: */
1681: static int dbFindCtl(struct bmap * bmp, int l2nb, int level, s64 * blkno)
1682: {
1683: int rc, leafidx, lev;
1684: s64 b, lblkno;
1685: struct dmapctl *dcp;
1686: int budmin;
1687: struct metapage *mp;
1688:
1689: /* starting at the specified dmap control page level and block
1690: * number, search down the dmap control levels for the starting
1691: * block number of a dmap page that contains or starts off
1692: * sufficient free blocks.
1693: */
1694: for (lev = level, b = *blkno; lev >= 0; lev--) {
1695: /* get the buffer of the dmap control page for the block
1696: * number and level (i.e. L0, L1, L2).
1697: */
1698: lblkno = BLKTOCTL(b, bmp->db_l2nbperpage, lev);
1699: mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
1700: if (mp == NULL)
1701: return -EIO;
1702: dcp = (struct dmapctl *) mp->data;
1703: budmin = dcp->budmin;
1704:
1705: if (dcp->leafidx != cpu_to_le32(CTLLEAFIND)) {
1706: jfs_error(bmp->db_ipbmap->i_sb,
1707: "Corrupt dmapctl page\n");
1708: release_metapage(mp);
1709: return -EIO;
1710: }
1711:
1712: /* search the tree within the dmap control page for
1713: * sufficient free space. if sufficient free space is found,
1714: * dbFindLeaf() returns the index of the leaf at which
1715: * free space was found.
1716: */
1717: rc = dbFindLeaf((dmtree_t *) dcp, l2nb, &leafidx, true);
1718:
1719: /* release the buffer.
1720: */
1721: release_metapage(mp);
1722:
1723: /* space found ?
1724: */
1725: if (rc) {
1726: if (lev != level) {
1727: jfs_error(bmp->db_ipbmap->i_sb,
1728: "dmap inconsistent\n");
1729: return -EIO;
1730: }
1731: return -ENOSPC;
1732: }
1733:
1734: /* adjust the block number to reflect the location within
1735: * the dmap control page (i.e. the leaf) at which free
1736: * space was found.
1737: */
1738: b += (((s64) leafidx) << budmin);
1739:
1740: /* we stop the search at this dmap control page level if
1741: * the number of blocks required is greater than or equal
1742: * to the maximum number of blocks described at the next
1743: * (lower) level.
1744: */
1745: if (l2nb >= budmin)
1746: break;
1747: }
1748:
1749: *blkno = b;
1750: return (0);
1751: }
SourceFile:fs/jfs/jfs_dmap.c]
|
| 18/2 |
2026/01/27 18:57 |
llm |
debugger |
0m
Model:
Tokens:
input: 18397
output: 40
thoughts: 1712
Thoughts: **Analysis of Out-of-Bounds Write in `dbFindLeaf`**
Okay, let me walk through my thought process on this. I've been examining a potential out-of-bounds write in the `dbFindLeaf` function within the `jfs_dmap.c` driver. The issue stems from the interaction between data read from disk and the bounds checking within the function, specifically during the tree traversal.
The root of the problem seems to lie within `dbFindCtl`, where `dcp` (the dmap control page) is read from disk. The critical point is that the function doesn't validate the `dcp->height` field against a known maximum tree height (e.g., `CTLTREESIZE`), before using it to control the loop iterations in `dbFindLeaf`. In `dbFindLeaf`, at line 2965, the height is used in a loop.
Here's where it gets interesting: even if `height` *is* correctly set (like 5 for `dmapctl`), the current bound check within the loop, `if (x + n > max_size)`, is off-by-one. This leads to the problem. Let me explain:
`dmapctl` tree, with max size 1365. With height 5:
* L0: 0
* L1: 1-4
* L2: 5-20
* L3: 21-84
* L4: 85-340
* L5: 341-1364
`k` runs 5,4,3,2,1.
Iteration k=5 (L1): ti=1. Loop x=1..4. Max index 4. `max_size`=1365. OK.
Iteration k=1 (L5): ti=341 (if path was all first children). Loop x=341..344. Max 344.
Max index at L5 is 1364.
So if `height` is correct (5), `x+n` will be at most 1364.
So `x+n` will not exceed 1364.
So `x+n` will not reach 1365.
So for `x+n` to reach 1365, `k` must allow one more level, so `dmt_height` must be > 5.
If `dmt_height` is 6.
Iteration k=1 (L6): ti would be calculated from L5 indices.
If we were at index 341 (first leaf of L5).
`ti = ((341 + 0) << 2) + 1 = 1364 + 1 = 1365`.
Then inner loop `x=1365`, `n=0`. `x+n=1365`.
Then `if (1365 > 1365)` is false.
Then access `stree[1365]` -> OOB.
Let's say `dcp->height` is, in fact, larger, say 6. The loop iterates too many times and index `ti` exceeds the bounds of the `stree` array, even with a correct tree of depth 5. The loop's bounds check allows accessing `stree[max_size]` which results in the OOB access.
The correct check would be `if (x + n >= max_size)`. This prevents the OOB access by handling the `x + n` at `max_size` edge case. The current `> max_size` check incorrectly allows access to index `max_size`.
Importantly, `dbFindLeaf` is designed to traverse a tree and `max_size` is passed to the function to limit the search. The `x + n > max_size` check is intended to prevent OOB accesses, but its logic is incorrect.
`max_size` is derived from `CTLTREESIZE` or `TREESIZE` based on the context. Let me make sure those sizes are correct. `CTLTREESIZE` is 1365, which corresponds to indices 0-1364. So the check `>= 1365` *is* correct for `dmapctl`. Similarly, `TREESIZE` is 341, so indices range from 0 to 340. The bug exists in both cases.
Also the `k > 0` condition in the loop, iterated `tp->dmt
|
| 19/2 |
2026/01/27 18:57 |
tool |
codesearch-find-references |
0m
Error:
Args: map[Name:max_size SourceTreePrefix:fs/jfs/jfs_dmap.c]
Results: map[References:<nil> TruncatedOutput:false]
|
| 20/2 |
2026/01/27 18:57 |
llm |
debugger |
0m
Model:
Tokens:
input: 21195
output: 42
thoughts: 64
Thoughts: **Analyzing `max_size` in `dbFindLeaf`**
Okay, so I was initially thinking about the search pattern itself, but now I've taken a look at the code. `max_size` is a local variable within `dbFindLeaf`. My concern now is whether I've missed something. To be completely sure, I'm going to shift my focus and broaden the scope. I'll search for all the usages of `CTLTREESIZE` within `jfs_dmap.c`. That should give me a better understanding of how this size constant is used and whether any other areas could potentially be affected or are similarly safe in their current implementation. This broader search should ensure I don't overlook any related usage patterns or vulnerabilities.
|
| 21/2 |
2026/01/27 18:57 |
tool |
codesearch-find-references |
0m
Error:
Args: map[Name:CTLTREESIZE SourceTreePrefix:fs/jfs/jfs_dmap.c]
Results: map[References:<nil> TruncatedOutput:false]
|
| 22/2 |
2026/01/27 18:57 |
llm |
debugger |
0m
Model:
Tokens:
input: 21483
output: 33
thoughts: 109
Thoughts: **Debugging the `dbFindLeaf` Crash**
Okay, so I'm hitting a crash, and it seems to be in `dbFindLeaf`. Right, `CTLTREESIZE` is a macro, and my initial instinct is to use `find-references`, but I know `find-references` operates on entities. I could also just `grep` via `codesearch-definition-source` or go old-school and manually read the likely functions, but I want to be surgical. The crash is *specifically* in `dbFindLeaf`, so let's start there.
Hold on, before I dig too deep, let's take a step back. I should check where else `dbFindLeaf` is being called to get a better handle on the potential root cause. Looking at the call stack, I see `dbFindCtl` calls it. Hmm, any others? Ah, looks like `dbAllocDmapLev` calls it as well. Okay, let's investigate the context of those calls and see if we can identify any discrepancies. That should give me the crucial context I need to diagnose the error.
|
| 23/2 |
2026/01/27 18:57 |
tool |
codesearch-find-references |
0m
Args: map[Name:dbFindLeaf SourceTreePrefix:fs/jfs/]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:dbAllocDmapLev SourceFile:fs/jfs/jfs_dmap.c SourceLine:1969] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:dbFindCtl SourceFile:fs/jfs/jfs_dmap.c SourceLine:1717]] TruncatedOutput:false]
|
| 24/2 |
2026/01/27 18:57 |
llm |
debugger |
0m
Model:
Tokens:
input: 21992
output: 46
thoughts: 33
Thoughts: Okay, here's my take on those thoughts, framed from a technical expert's perspective:
**Investigating the Data Map Level Allocation**
Right, so this code path is also called from `dbAllocDmapLev`. That's important to keep in mind; any behavior here could impact that function as well. Now, the key is to understand the context and how height validation, if any, is performed. The next logical step is to dive into `dbAllocDmapLev` to see precisely *how* it's using (or not using) the logic we're looking at, especially regarding any validation related to level height. Understanding that calling context is crucial for tracing the code and how the validation fits into the bigger picture of the data map level allocation. I need to figure out what validations are already being handled and if there's any redundancy.
|
| 25/2 |
2026/01/27 18:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeLines:true Name:dbAllocDmapLev]
Results: map[SourceCode:1929: /*
1930: * NAME: dbAllocDmapLev()
1931: *
1932: * FUNCTION: attempt to allocate a specified number of contiguous blocks
1933: * from a specified dmap.
1934: *
1935: * this routine checks if the contiguous blocks are available.
1936: * if so, nblocks of blocks are allocated; otherwise, ENOSPC is
1937: * returned.
1938: *
1939: * PARAMETERS:
1940: * mp - pointer to bmap descriptor
1941: * dp - pointer to dmap to attempt to allocate blocks from.
1942: * l2nb - log2 number of contiguous block desired.
1943: * nblocks - actual number of contiguous block desired.
1944: * results - on successful return, set to the starting block number
1945: * of the newly allocated range.
1946: *
1947: * RETURN VALUES:
1948: * 0 - success
1949: * -ENOSPC - insufficient disk resources
1950: * -EIO - i/o error
1951: *
1952: * serialization: IREAD_LOCK(ipbmap), e.g., from dbAlloc(), or
1953: * IWRITE_LOCK(ipbmap), e.g., dbAllocCtl(), held on entry/exit;
1954: */
1955: static int
1956: dbAllocDmapLev(struct bmap * bmp,
1957: struct dmap * dp, int nblocks, int l2nb, s64 * results)
1958: {
1959: s64 blkno;
1960: int leafidx, rc;
1961:
1962: /* can't be more than a dmaps worth of blocks */
1963: assert(l2nb <= L2BPERDMAP);
1964:
1965: /* search the tree within the dmap page for sufficient
1966: * free space. if sufficient free space is found, dbFindLeaf()
1967: * returns the index of the leaf at which free space was found.
1968: */
1969: if (dbFindLeaf((dmtree_t *) &dp->tree, l2nb, &leafidx, false))
1970: return -ENOSPC;
1971:
1972: if (leafidx < 0)
1973: return -EIO;
1974:
1975: /* determine the block number within the file system corresponding
1976: * to the leaf at which free space was found.
1977: */
1978: blkno = le64_to_cpu(dp->start) + (leafidx << L2DBWORD);
1979:
1980: /* if not all bits of the dmap word are free, get the starting
1981: * bit number within the dmap word of the required string of free
1982: * bits and adjust the block number with this value.
1983: */
1984: if (dp->tree.stree[leafidx + LEAFIND] < BUDMIN)
1985: blkno += dbFindBits(le32_to_cpu(dp->wmap[leafidx]), l2nb);
1986:
1987: /* allocate the blocks */
1988: if ((rc = dbAllocDmap(bmp, dp, blkno, nblocks)) == 0)
1989: *results = blkno;
1990:
1991: return (rc);
1992: }
SourceFile:fs/jfs/jfs_dmap.c]
|
| 26/2 |
2026/01/27 18:58 |
llm |
debugger |
0m
Model:
Tokens:
input: 23314
output: 453
thoughts: 1522
Thoughts: **Analysis of the JFS Dmap Crash**
Okay, so I've got this. The crash is happening in `dbFindLeaf` at `fs/jfs/jfs_dmap.c:2976`. I can see from the call stack that `dbFindCtl` is calling `dbFindLeaf`, passing `is_ctl=true`. This means we're dealing with the control dmap structure and `max_size` is `CTLTREESIZE`, which is 1365. The crash is an out-of-bounds array access on `tp->dmt_stree[x + n]`. UBSAN is reporting the access as index 1365, confirming that `is_ctl` is true and that it's accessing the `t2.stree` member, which has a size of 1365.
The key is in this bounds check: `if (x + n > max_size)`. With `max_size` being 1365, the condition `x + n > 1365` *should* prevent the out-of-bounds access. However, because the index starts at 0, the correct condition should be `x + n >= max_size` because 1365 is a valid address and is one higher than 1364, the highest valid index for an array of size 1365. This allows the loop to calculate an index that's *equal* to `max_size` which results in the OOB read.
The root cause? The `dmt_height` field on disk is getting corrupted or somehow set to a value higher than it should be, likely due to filesystem corruption. This leads to `dbFindLeaf` looping too many times, because the loop condition is based on `dmt_height`. There isn't a check for the height in the calling function, `dbFindCtl`, so the corruption is not caught early.
The fix is simple: change the bounds check in `dbFindLeaf` from `>` to `>=`. That one character fixes it. I know I have to be precise, and this explanation covers it all. I can't think of any edge cases. I'm ready to write the summary.
|
| 27/1 |
2026/01/27 18:58 |
action |
kernel-scratch-checkouter |
0m
Results: map[KernelScratchSrc:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/tmp/tmp3378643586]
|
| 28/1 |
2026/01/27 18:58 |
loop |
|
12m
|
| 29/2 |
2026/01/27 18:58 |
iteration |
0 |
12m
|
| 30/3 |
2026/01/27 18:58 |
agent |
patch-generator |
2m
Model:
Instruction:
You are an experienced Linux kernel developer tasked with creating a fix for a kernel bug.
Use the codeedit tool to do code edits.
Note: you will not see your changes when looking at the code using codesearch tools.
Your final reply should contain explanation of what you did in the patch and why.
Prefer calling several tools at the same time to save round-trips.
Prompt:
The crash that corresponds to the bug is:
------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in /usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/5452af61ab2e1f5601403fe379188fc9d8a831af/fs/jfs/jfs_dmap.c:2976:16
index 1365 is out of range for type 's8[1365]' (aka 'signed char[1365]')
CPU: 1 UID: 0 PID: 6199 Comm: syz-executor257 Not tainted syzkaller #1 PREEMPT_{RT,(full)}
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x10e/0x190 lib/dump_stack.c:120
ubsan_epilogue lib/ubsan.c:233 [inline]
__ubsan_handle_out_of_bounds+0x115/0x140 lib/ubsan.c:455
dbFindLeaf+0x308/0x520 fs/jfs/jfs_dmap.c:2976
dbFindCtl+0x267/0x520 fs/jfs/jfs_dmap.c:1717
dbAllocAny fs/jfs/jfs_dmap.c:1527 [inline]
dbAlloc+0x5fd/0xba0 fs/jfs/jfs_dmap.c:878
diNewIAG fs/jfs/jfs_imap.c:2510 [inline]
diAllocExt fs/jfs/jfs_imap.c:1905 [inline]
diAllocAG+0xcf0/0x1db0 fs/jfs/jfs_imap.c:1669
diAlloc+0x1d4/0x1670 fs/jfs/jfs_imap.c:1590
ialloc+0x8c/0x8f0 fs/jfs/jfs_inode.c:56
jfs_mkdir+0x193/0xa70 fs/jfs/namei.c:225
vfs_mkdir+0x530/0x5d0 fs/namei.c:5139
do_mkdirat+0x27a/0x4b0 fs/namei.c:5173
__do_sys_mkdir fs/namei.c:5200 [inline]
__se_sys_mkdir fs/namei.c:5198 [inline]
__x64_sys_mkdir+0x6c/0x80 fs/namei.c:5198
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe8/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc490daf897
Code: 1f 40 00 48 89 f2 b9 00 01 00 00 48 89 fe bf 9c ff ff ff e9 7b 37 03 00 66 2e 0f 1f 84 00 00 00 00 00 90 b8 53 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d0 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fc490d51038 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 0000200000000200 RCX: 00007fc490daf897
RDX: 0000000002b1247d RSI: 00000000000001ff RDI: 00002000000002c0
RBP: 0000000000000000 R08: 00000000000000fc R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 00002000000002c0
R13: 00007fc490d510d0 R14: 0000000000000000 R15: 0000000000000000
</TASK>
---[ end trace ]---
The explanation of the root cause of the bug is:
The root cause of this crash is an off-by-one error in the bounds check within the `dbFindLeaf` function in `fs/jfs/jfs_dmap.c`.
The function `dbFindLeaf` iterates through the levels of a dmap tree to find a leaf with sufficient free blocks. The number of iterations is determined by `tp->dmt_height`, which is read from the filesystem image (disk). The crash occurs when `tp->dmt_height` is corrupted (too large), causing the loop to descend deeper than the defined tree structure allows, resulting in the calculated index `x + n` exceeding the valid range of the `tp->dmt_stree` array.
Specifically:
1. The array `tp->dmt_stree` has a size of `CTLTREESIZE` (1365) when `is_ctl` is true (which is the case in the stack trace, called from `dbFindCtl`). The valid indices are `0` to `1364`.
2. The code includes a bounds check at line 2974: `if (x + n > max_size)`.
3. `max_size` is set to `CTLTREESIZE` (1365).
4. When `x + n` reaches `1365`, the condition `1365 > 1365` evaluates to false, allowing execution to proceed.
5. The code then attempts to access `tp->dmt_stree[1365]` at line 2976, triggering the UBSAN array-index-out-of-bounds error.
The bounds check should use `>=` instead of `>` to correctly handle the case where the index equals the array size.
**Fix:**
Change the bounds check in `fs/jfs/jfs_dmap.c` from:
```c
if (x + n > max_size)
```
to:
```c
if (x + n >= max_size)
```
Reply: The bug is an off-by-one error in the `dbFindLeaf` function in `fs/jfs/jfs_dmap.c`.
The code iterates over a dmap tree to find free blocks. The loop calculates an index `x + n` into the `tp->dmt_stree` array. The bounds check `if (x + n > max_size)` allows the index to be equal to `max_size`.
Since `max_size` represents the size of the array (e.g., 1365 for `CTLTREESIZE`), and arrays are 0-indexed, an index of `max_size` is out of bounds. The valid indices are `0` to `max_size - 1`.
The crash report shows UBSAN detecting an access at index 1365 for an array of size 1365.
This happens when `tp->dmt_height` is corrupted (too large), causing the loop to go deeper than expected and the index to grow beyond the tree size.
The fix is to change the condition to `if (x + n >= max_size)` to ensure the index stays within valid bounds `[0, max_size - 1]`.
The patch modifies `fs/jfs/jfs_dmap.c`:
```c
<<<<
if (x + n > max_size)
return -ENOSPC;
====
if (x + n >= max_size)
return -ENOSPC;
>>>>
```
|
| 31/4 |
2026/01/27 18:58 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 4098
output: 44
thoughts: 230
Thoughts: **Analyzing a UBSAN Array-Index-Out-of-Bounds Error in JFS**
Okay, so I've got a UBSAN report here indicating an array-index-out-of-bounds error in `fs/jfs/jfs_dmap.c`, specifically at line 2976. The error details point to an access at index 1365 for an array of type `s8[1365]`. My immediate thought is, based on the description, this almost certainly comes down to an off-by-one error in a bounds check within the `dbFindLeaf` function. The explanation flags that `max_size` is 1365, and the check, as implemented, doesn't correctly cover when `x + n` equals `max_size`.
My next step is clear: I need to dive into the code. I'll need to locate the `dbFindLeaf` function within `fs/jfs/jfs_dmap.c`. I will then zero in on the vicinity of line 2976 and carefully review the bounds checking logic surrounding the array access. I'll be looking for where the variable `x` and `n` are calculated, and how they relate to `max_size`. Given my experience, I expect that a subtle error in this check, potentially in the inequality used or in an off-by-one comparison, is the root cause.
|
| 32/4 |
2026/01/27 18:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeLines:true Name:dbFindLeaf]
Results: map[SourceCode:2924: /*
2925: * NAME: dbFindLeaf()
2926: *
2927: * FUNCTION: search a dmtree_t for sufficient free blocks, returning
2928: * the index of a leaf describing the free blocks if
2929: * sufficient free blocks are found.
2930: *
2931: * the search starts at the top of the dmtree_t tree and
2932: * proceeds down the tree to the leftmost leaf with sufficient
2933: * free space.
2934: *
2935: * PARAMETERS:
2936: * tp - pointer to the tree to be searched.
2937: * l2nb - log2 number of free blocks to search for.
2938: * leafidx - return pointer to be set to the index of the leaf
2939: * describing at least l2nb free blocks if sufficient
2940: * free blocks are found.
2941: * is_ctl - determines if the tree is of type ctl
2942: *
2943: * RETURN VALUES:
2944: * 0 - success
2945: * -ENOSPC - insufficient free blocks.
2946: */
2947: static int dbFindLeaf(dmtree_t *tp, int l2nb, int *leafidx, bool is_ctl)
2948: {
2949: int ti, n = 0, k, x = 0;
2950: int max_size, max_idx;
2951:
2952: max_size = is_ctl ? CTLTREESIZE : TREESIZE;
2953: max_idx = is_ctl ? LPERCTL : LPERDMAP;
2954:
2955: /* first check the root of the tree to see if there is
2956: * sufficient free space.
2957: */
2958: if (l2nb > tp->dmt_stree[ROOT])
2959: return -ENOSPC;
2960:
2961: /* sufficient free space available. now search down the tree
2962: * starting at the next level for the leftmost leaf that
2963: * describes sufficient free space.
2964: */
2965: for (k = le32_to_cpu(tp->dmt_height), ti = 1;
2966: k > 0; k--, ti = ((ti + n) << 2) + 1) {
2967: /* search the four nodes at this level, starting from
2968: * the left.
2969: */
2970: for (x = ti, n = 0; n < 4; n++) {
2971: /* sufficient free space found. move to the next
2972: * level (or quit if this is the last level).
2973: */
2974: if (x + n > max_size)
2975: return -ENOSPC;
2976: if (l2nb <= tp->dmt_stree[x + n])
2977: break;
2978: }
2979:
2980: /* better have found something since the higher
2981: * levels of the tree said it was here.
2982: */
2983: assert(n < 4);
2984: }
2985: if (le32_to_cpu(tp->dmt_leafidx) >= max_idx)
2986: return -ENOSPC;
2987:
2988: /* set the return to the leftmost leaf describing sufficient
2989: * free space.
2990: */
2991: *leafidx = x + n - le32_to_cpu(tp->dmt_leafidx);
2992:
2993: return (0);
2994: }
SourceFile:fs/jfs/jfs_dmap.c]
|
| 33/4 |
2026/01/27 18:58 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 5810
output: 41
thoughts: 445
Thoughts: **Analyzing the Array Index Out-of-Bounds Error**
Okay, let's break this down. I'm looking at this C code, specifically this loop:
```c
2970: for (x = ti, n = 0; n < 4; n++) {
2971: /* sufficient free space found. move to the next
2972: * level (or quit if this is the last level).
2973: */
2974: if (x + n > max_size)
2975: return -ENOSPC;
2976: if (l2nb <= tp->dmt_stree[x + n])
2977: break;
2978: }
```
The error report says `index 1365 is out of range for type 's8[1365]'`. So, the problem is clearly with the access to `tp->dmt_stree` at line 2976. This array is being indexed by `x + n`. Now, the error description has given us the crucial piece of information that the array's size is 1365. That means valid indices are 0 to 1364.
Looking at the initialization of `max_size`:
```c
2952: max_size = is_ctl ? CTLTREESIZE : TREESIZE;
```
Since the error message tells us the array is `s8[1365]`, we know that `CTLTREESIZE` must be 1365, as determined by the ternary operator when `is_ctl` is true.
The crucial check is `if (x + n > max_size)`. Now, let's trace this. When `x + n` equals 1365, the comparison becomes 1365 > 1365, which evaluates to false. So, the code *should* proceed to line 2976. But then, it tries to access `tp->dmt_stree[1365]`, and that's precisely where the out-of-bounds error occurs because the valid indices are 0 through 1364.
The suggested fix, changing the `>` to `>=` in the conditional, immediately makes sense. That conditional should prevent the array out-of-bounds access. The corrected conditional would now be: `if (x + n >= max_size)`. This then guards against indices equal to `max_size`.
Before I sign off on this, though, I need to double-check the definitions of `CTLTREESIZE` and `TREESIZE` just to be absolutely certain of their values and any potential dependencies. It's always good to verify the assumptions. But so far, this looks like a straightforward fix for an off-by-one error.
|
| 34/4 |
2026/01/27 18:59 |
tool |
codesearch-find-references |
0m
Error:
Args: map[ContextFile:fs/jfs/jfs_dmap.c Name:CTLTREESIZE]
Results: map[References:<nil> TruncatedOutput:false]
|
| 35/4 |
2026/01/27 18:59 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 6962
output: 22
thoughts: 176
Thoughts: **Investigating the `CTLTREESIZE` Macro**
Okay, so `CTLTREESIZE`... that looks like a macro. My initial instinct is to check `fs/jfs/jfs_dmap.h` or potentially within `fs/jfs/jfs_dmap.c` itself. It could be defined in either place, or possibly in an included header file. Since I don't immediately know where it's defined, I'll start by taking a look at the top of `fs/jfs/jfs_dmap.c` to see if there are any obvious includes or definitions declared directly there.
Alternatively, I could do a search across the entire file tree but restrict it to `fs/jfs`. That's a reasonable option.
But wait a minute, `codesearch-find-references` *should* be able to locate this, even if it's a macro, right? It usually does a pretty good job. It might save some time, if that's the case. It is a good option.
Alright, let's just jump straight to `fs/jfs/jfs_dmap.h` first. That seems like the most likely and efficient first step.
|
| 36/4 |
2026/01/27 18:59 |
tool |
codesearch-dir-index |
0m
Args:
Results: map[Files:[acl.c file.c inode.c ioctl.c jfs_acl.h jfs_btree.h jfs_debug.c jfs_debug.h jfs_dinode.h jfs_discard.c jfs_discard.h jfs_dmap.c jfs_dmap.h jfs_dtree.c jfs_dtree.h jfs_extent.c jfs_extent.h jfs_filsys.h jfs_imap.c jfs_imap.h jfs_incore.h jfs_inode.c jfs_inode.h jfs_lock.h jfs_logmgr.c jfs_logmgr.h jfs_metapage.c jfs_metapage.h jfs_mount.c jfs_superblock.h jfs_txnmgr.c jfs_txnmgr.h jfs_types.h jfs_umount.c jfs_unicode.c jfs_unicode.h jfs_xattr.h jfs_xtree.c jfs_xtree.h namei.c resize.c super.c symlink.c xattr.c] Subdirs:<nil>]
|
| 37/4 |
2026/01/27 18:59 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 7838
output: 27
thoughts: 25
Thoughts: Here's my analysis of the situation:
**Investigating `jfs_dmap.h` for `CTLTREESIZE`**
Okay, so I'm looking at `jfs_dmap.h`. Immediately, my brain goes into search mode. I need to find `CTLTREESIZE`. This likely means I'm working with JFS and the disk map, and `CTLTREESIZE` is almost certainly a crucial constant related to control tree size or some allocation unit within the file system. Now, I have to efficiently read this header file; I'm going to look for constants, macros, and defines, that sort of thing. I'll mentally categorize the definitions as they pop up to understand the relationship of this constant to other structures. Let's dig in.
|
| 38/4 |
2026/01/27 18:59 |
tool |
read-file |
0m
Args: map[File:fs/jfs/jfs_dmap.h]
Results: map[Contents:/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Copyright (C) International Business Machines Corp., 2000-2002
*/
#ifndef _H_JFS_DMAP
#define _H_JFS_DMAP
#include "jfs_txnmgr.h"
#define BMAPVERSION 1 /* version number */
#define TREESIZE (256+64+16+4+1) /* size of a dmap tree */
#define LEAFIND (64+16+4+1) /* index of 1st leaf of a dmap tree */
#define LPERDMAP 256 /* num leaves per dmap tree */
#define L2LPERDMAP 8 /* l2 number of leaves per dmap tree */
#define DBWORD 32 /* # of blks covered by a map word */
#define L2DBWORD 5 /* l2 # of blks covered by a mword */
#define BUDMIN L2DBWORD /* max free string in a map word */
#define BPERDMAP (LPERDMAP * DBWORD) /* num of blks per dmap */
#define L2BPERDMAP 13 /* l2 num of blks per dmap */
#define CTLTREESIZE (1024+256+64+16+4+1) /* size of a dmapctl tree */
#define CTLLEAFIND (256+64+16+4+1) /* idx of 1st leaf of a dmapctl tree */
#define LPERCTL 1024 /* num of leaves per dmapctl tree */
#define L2LPERCTL 10 /* l2 num of leaves per dmapctl tree */
#define ROOT 0 /* index of the root of a tree */
#define NOFREE ((s8) -1) /* no blocks free */
#define MAXAG 128 /* max number of allocation groups */
#define L2MAXAG 7 /* l2 max num of AG */
#define L2MINAGSZ 25 /* l2 of minimum AG size in bytes */
#define BMAPBLKNO 0 /* lblkno of bmap within the map */
/*
* maximum l2 number of disk blocks at the various dmapctl levels.
*/
#define L2MAXL0SIZE (L2BPERDMAP + 1 * L2LPERCTL)
#define L2MAXL1SIZE (L2BPERDMAP + 2 * L2LPERCTL)
#define L2MAXL2SIZE (L2BPERDMAP + 3 * L2LPERCTL)
/*
* maximum number of disk blocks at the various dmapctl levels.
*/
#define MAXL0SIZE ((s64)1 << L2MAXL0SIZE)
#define MAXL1SIZE ((s64)1 << L2MAXL1SIZE)
#define MAXL2SIZE ((s64)1 << L2MAXL2SIZE)
#define MAXMAPSIZE MAXL2SIZE /* maximum aggregate map size */
/*
* determine the maximum free string for four (lower level) nodes
* of the tree.
*/
static inline signed char TREEMAX(signed char *cp)
{
signed char tmp1, tmp2;
tmp1 = max(*(cp+2), *(cp+3));
tmp2 = max(*(cp), *(cp+1));
return max(tmp1, tmp2);
}
/*
* convert disk block number to the logical block number of the dmap
* describing the disk block. s is the log2(number of logical blocks per page)
*
* The calculation figures out how many logical pages are in front of the dmap.
* - the number of dmaps preceding it
* - the number of L0 pages preceding its L0 page
* - the number of L1 pages preceding its L1 page
* - 3 is added to account for the L2, L1, and L0 page for this dmap
* - 1 is added to account for the control page of the map.
*/
#define BLKTODMAP(b,s) \
((((b) >> 13) + ((b) >> 23) + ((b) >> 33) + 3 + 1) << (s))
/*
* convert disk block number to the logical block number of the LEVEL 0
* dmapctl describing the disk block. s is the log2(number of logical blocks
* per page)
*
* The calculation figures out how many logical pages are in front of the L0.
* - the number of dmap pages preceding it
* - the number of L0 pages preceding it
* - the number of L1 pages preceding its L1 page
* - 2 is added to account for the L2, and L1 page for this L0
* - 1 is added to account for the control page of the map.
*/
#define BLKTOL0(b,s) \
(((((b) >> 23) << 10) + ((b) >> 23) + ((b) >> 33) + 2 + 1) << (s))
/*
* convert disk block number to the logical block number of the LEVEL 1
* dmapctl describing the disk block. s is the log2(number of logical blocks
* per page)
*
* The calculation figures out how many logical pages are in front of the L1.
* - the number of dmap pages preceding it
* - the number of L0 pages preceding it
* - the number of L1 pages preceding it
* - 1 is added to account for the L2 page
* - 1 is added to account for the control page of the map.
*/
#define BLKTOL1(b,s) \
(((((b) >> 33) << 20) + (((b) >> 33) << 10) + ((b) >> 33) + 1 + 1) << (s))
/*
* convert disk block number to the logical block number of the dmapctl
* at the specified level which describes the disk block.
*/
#define BLKTOCTL(b,s,l) \
(((l) == 2) ? 1 : ((l) == 1) ? BLKTOL1((b),(s)) : BLKTOL0((b),(s)))
/*
* convert aggregate map size to the zero origin dmapctl level of the
* top dmapctl.
*/
#define BMAPSZTOLEV(size) \
(((size) <= MAXL0SIZE) ? 0 : ((size) <= MAXL1SIZE) ? 1 : 2)
/* convert disk block number to allocation group number.
*/
#define BLKTOAG(b,sbi) ((b) >> ((sbi)->bmap->db_agl2size))
/* convert allocation group number to starting disk block
* number.
*/
#define AGTOBLK(a,ip) \
((s64)(a) << (JFS_SBI((ip)->i_sb)->bmap->db_agl2size))
/*
* dmap summary tree
*
* dmaptree must be consistent with dmapctl.
*/
struct dmaptree {
__le32 nleafs; /* 4: number of tree leafs */
__le32 l2nleafs; /* 4: l2 number of tree leafs */
__le32 leafidx; /* 4: index of first tree leaf */
__le32 height; /* 4: height of the tree */
s8 budmin; /* 1: min l2 tree leaf value to combine */
s8 stree[TREESIZE]; /* TREESIZE: tree */
u8 pad[2]; /* 2: pad to word boundary */
}; /* - 360 - */
/*
* dmap page per 8K blocks bitmap
*/
struct dmap {
__le32 nblocks; /* 4: num blks covered by this dmap */
__le32 nfree; /* 4: num of free blks in this dmap */
__le64 start; /* 8: starting blkno for this dmap */
struct dmaptree tree; /* 360: dmap tree */
u8 pad[1672]; /* 1672: pad to 2048 bytes */
__le32 wmap[LPERDMAP]; /* 1024: bits of the working map */
__le32 pmap[LPERDMAP]; /* 1024: bits of the persistent map */
}; /* - 4096 - */
/*
* disk map control page per level.
*
* dmapctl must be consistent with dmaptree.
*/
struct dmapctl {
__le32 nleafs; /* 4: number of tree leafs */
__le32 l2nleafs; /* 4: l2 number of tree leafs */
__le32 leafidx; /* 4: index of the first tree leaf */
__le32 height; /* 4: height of tree */
s8 budmin; /* 1: minimum l2 tree leaf value */
s8 stree[CTLTREESIZE]; /* CTLTREESIZE: dmapctl tree */
u8 pad[2714]; /* 2714: pad to 4096 */
}; /* - 4096 - */
/*
* common definition for dmaptree within dmap and dmapctl
*/
typedef union dmtree {
struct dmaptree t1;
struct dmapctl t2;
} dmtree_t;
/* macros for accessing fields within dmtree */
#define dmt_nleafs t1.nleafs
#define dmt_l2nleafs t1.l2nleafs
#define dmt_leafidx t1.leafidx
#define dmt_height t1.height
#define dmt_budmin t1.budmin
#define dmt_stree t2.stree
/*
* on-disk aggregate disk allocation map descriptor.
*/
struct dbmap_disk {
__le64 dn_mapsize; /* 8: number of blocks in aggregate */
__le64 dn_nfree; /* 8: num free blks in aggregate map */
__le32 dn_l2nbperpage; /* 4: number of blks per page */
__le32 dn_numag; /* 4: total number of ags */
__le32 dn_maxlevel; /* 4: number of active ags */
__le32 dn_maxag; /* 4: max active alloc group number */
__le32 dn_agpref; /* 4: preferred alloc group (hint) */
__le32 dn_aglevel; /* 4: dmapctl level holding the AG */
__le32 dn_agheight; /* 4: height in dmapctl of the AG */
__le32 dn_agwidth; /* 4: width in dmapctl of the AG */
__le32 dn_agstart; /* 4: start tree index at AG height */
__le32 dn_agl2size; /* 4: l2 num of blks per alloc group */
__le64 dn_agfree[MAXAG];/* 8*MAXAG: per AG free count */
__le64 dn_agsize; /* 8: num of blks per alloc group */
s8 dn_maxfreebud; /* 1: max free buddy system */
u8 pad[3007]; /* 3007: pad to 4096 */
}; /* - 4096 - */
struct dbmap {
s64 dn_mapsize; /* number of blocks in aggregate */
s64 dn_nfree; /* num free blks in aggregate map */
int dn_l2nbperpage; /* number of blks per page */
int dn_numag; /* total number of ags */
int dn_maxlevel; /* number of active ags */
int dn_maxag; /* max active alloc group number */
int dn_agpref; /* preferred alloc group (hint) */
int dn_aglevel; /* dmapctl level holding the AG */
int dn_agheight; /* height in dmapctl of the AG */
int dn_agwidth; /* width in dmapctl of the AG */
int dn_agstart; /* start tree index at AG height */
int dn_agl2size; /* l2 num of blks per alloc group */
s64 dn_agfree[MAXAG]; /* per AG free count */
s64 dn_agsize; /* num of blks per alloc group */
signed char dn_maxfreebud; /* max free buddy system */
}; /* - 4096 - */
/*
* in-memory aggregate disk allocation map descriptor.
*/
struct bmap {
struct dbmap db_bmap; /* on-disk aggregate map descriptor */
struct inode *db_ipbmap; /* ptr to aggregate map incore inode */
struct mutex db_bmaplock; /* aggregate map lock */
atomic_t db_active[MAXAG]; /* count of active, open files in AG */
u32 *db_DBmap;
};
/* macros for accessing fields within in-memory aggregate map descriptor */
#define db_mapsize db_bmap.dn_mapsize
#define db_nfree db_bmap.dn_nfree
#define db_agfree db_bmap.dn_agfree
#define db_agsize db_bmap.dn_agsize
#define db_agl2size db_bmap.dn_agl2size
#define db_agwidth db_bmap.dn_agwidth
#define db_agheight db_bmap.dn_agheight
#define db_agstart db_bmap.dn_agstart
#define db_numag db_bmap.dn_numag
#define db_maxlevel db_bmap.dn_maxlevel
#define db_aglevel db_bmap.dn_aglevel
#define db_agpref db_bmap.dn_agpref
#define db_maxag db_bmap.dn_maxag
#define db_maxfreebud db_bmap.dn_maxfreebud
#define db_l2nbperpage db_bmap.dn_l2nbperpage
/*
* macros for various conversions needed by the allocators.
* blkstol2(), cntlz(), and cnttz() are operating system dependent functions.
*/
/* convert number of blocks to log2 number of blocks, rounding up to
* the next log2 value if blocks is not a l2 multiple.
*/
#define BLKSTOL2(d) (blkstol2(d))
/* convert number of leafs to log2 leaf value */
#define NLSTOL2BSZ(n) (31 - cntlz((n)) + BUDMIN)
/* convert leaf index to log2 leaf value */
#define LITOL2BSZ(n,m,b) ((((n) == 0) ? (m) : cnttz((n))) + (b))
/* convert a block number to a dmap control leaf index */
#define BLKTOCTLLEAF(b,m) \
(((b) & (((s64)1 << ((m) + L2LPERCTL)) - 1)) >> (m))
/* convert log2 leaf value to buddy size */
#define BUDSIZE(s,m) (1 << ((s) - (m)))
/*
* external references.
*/
extern int dbMount(struct inode *ipbmap);
extern int dbUnmount(struct inode *ipbmap, int mounterror);
extern int dbFree(struct inode *ipbmap, s64 blkno, s64 nblocks);
extern int dbUpdatePMap(struct inode *ipbmap,
int free, s64 blkno, s64 nblocks, struct tblock * tblk);
extern int dbNextAG(struct inode *ipbmap);
extern int dbAlloc(struct inode *ipbmap, s64 hint, s64 nblocks, s64 * results);
extern int dbReAlloc(struct inode *ipbmap,
s64 blkno, s64 nblocks, s64 addnblocks, s64 * results);
extern int dbSync(struct inode *ipbmap);
extern int dbAllocBottomUp(struct inode *ip, s64 blkno, s64 nblocks);
extern int dbExtendFS(struct inode *ipbmap, s64 blkno, s64 nblocks);
extern void dbFinalizeBmap(struct inode *ipbmap);
extern s64 dbMapFileSizeToMapSize(struct inode *ipbmap);
extern s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen);
#endif /* _H_JFS_DMAP */
]
|
| 39/4 |
2026/01/27 18:59 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 12330
output: 45
thoughts: 1913
Thoughts: **Analyzing the dmap Tree Index Out-of-Bounds Error**
Okay, so I've been digging into this UBSAN report and trying to understand this array out-of-bounds error. The core of the issue seems to be how the `dmtree_t` union interacts with the `dbFindLeaf` function and its access to the `stree` array.
First, I confirmed the sizes: `CTLTREESIZE` is 1365 and `TREESIZE` is 341. The `dmtree_t` union lets us treat a memory region as either a `dmaptree` or a `dmapctl`. The critical part is that `dmapctl` has a `s8 stree[CTLTREESIZE]` (1365 bytes), while `dmaptree` has `s8 stree[TREESIZE]` (341 bytes).
The function `dbFindLeaf` takes a `dmtree_t *tp` and uses `dmt_stree`, which is actually `t2.stree`. This means that regardless of whether `tp` is logically a `dmaptree` or a `dmapctl`, the code is always *physically* accessing the larger array, the one sized 1365 bytes.
The code checks `if (x + n > max_size)`. Here's where the problem arises: If `is_ctl` is false, `max_size` is set to `TREESIZE` (341); if `is_ctl` is true, `max_size` is set to `CTLTREESIZE` (1365). The UBSAN report shows an access out of bounds at index 1365. That implies that `is_ctl` is indeed true, because the check `x+n > 341` would have been triggered before it reached 1365.
Now, here's the tricky part. Even if `is_ctl` is false, the code *should* be checking against the logical size of 341. But, because of the union, the physical memory layout is still the larger array (1365). Accessing `stree[341]` would be out of bounds for the `dmaptree`'s view (0-340) but *within* the allocated size for `t2.stree` (0-1364). UBSAN somehow knows the real object size.
The actual crash at index 1365 confirms `is_ctl` is true. `max_size` became 1365. The condition `if (1365 > 1365)` is false, and then the code tries to access `stree[1365]`, boom. This means the problem is with the bounds check itself, and the fix is to use `>=`. The code should be `if (x + n >= max_size)`
I then need to verify the loop that calculates these array indices, specifically:
```c
for (k = le32_to_cpu(tp->dmt_height), ti = 1;
k > 0; k--, ti = ((ti + n) << 2) + 1) {
for (x = ti, n = 0; n < 4; n++) {
if (x + n > max_size)
return -ENOSPC;
if (l2nb <= tp->dmt_stree[x + n])
break;
}
}
```
The loop iterates down the tree, and the crucial part is how `ti` is updated in each iteration. It starts at 1, and in each level it checks `ti` to `ti + 3`. Then updates `ti` as `((ti + n) << 2) + 1`.
If the tree height is corrupted, or if the logic has some flaw, `ti` (and thus `x`) can potentially grow too large, eventually leading to `x+n` exceeding the intended bounds of the array. The `x + n >= max_size` check will catch an out-of-bounds access.
So, in conclusion, the original code had the wrong bounds check. We need to prevent access to the 1365th index.
The fix is to use `>=` instead of `>`.
The original author likely had a misunderstanding of how a zero-based array works, and where the error condition arises.
Now, I'm going to look for any other similar checks in the codebase.
|
| 40/4 |
2026/01/27 18:59 |
tool |
codesearch-find-references |
0m
Error:
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeSnippetLines:5 Name:max_size]
Results: map[References:<nil> TruncatedOutput:false]
|
| 41/4 |
2026/01/27 18:59 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 15315
output: 31
thoughts: 99
Thoughts: **Debugging a Potential Size Issue**
Okay, so I'm tracking down this `max_size` variable within `dbFindLeaf` – it seems like it's a local variable. I should probably re-examine the source code of `dbFindLeaf` directly, or just run a pattern search within it. I already have the code available, so that's the fastest approach.
Hmm, let me consider other functions that might be using similar logic. I know `dbFindCtl` calls `dbFindLeaf`, so that's a good starting point. Let's expand our search to `fs/jfs/jfs_dmap.c` in a broader sense. Maybe there are other places in that file with similar loop structures I can learn from.
|
| 42/4 |
2026/01/27 19:00 |
tool |
codesearch-file-index |
0m
Args: map[SourceFile:fs/jfs/jfs_dmap.c]
Results: map[Entities:[map[Kind:function Name:blkstol2] map[Kind:function Name:cntlz] map[Kind:function Name:cnttz] map[Kind:function Name:dbAdjCtl] map[Kind:function Name:dbAdjTree] map[Kind:function Name:dbAlloc] map[Kind:function Name:dbAllocAG] map[Kind:function Name:dbAllocAny] map[Kind:function Name:dbAllocBits] map[Kind:function Name:dbAllocBottomUp] map[Kind:function Name:dbAllocCtl] map[Kind:function Name:dbAllocDmap] map[Kind:function Name:dbAllocDmapBU] map[Kind:function Name:dbAllocDmapLev] map[Kind:function Name:dbAllocNear] map[Kind:function Name:dbAllocNext] map[Kind:function Name:dbBackSplit] map[Kind:function Name:dbDiscardAG] map[Kind:function Name:dbExtend] map[Kind:function Name:dbExtendFS] map[Kind:function Name:dbFinalizeBmap] map[Kind:function Name:dbFindBits] map[Kind:function Name:dbFindCtl] map[Kind:function Name:dbFindLeaf] map[Kind:function Name:dbFree] map[Kind:function Name:dbFreeBits] map[Kind:function Name:dbFreeDmap] map[Kind:function Name:dbGetL2AGSize] map[Kind:function Name:dbInitDmap] map[Kind:function Name:dbInitDmapCtl] map[Kind:function Name:dbInitDmapTree] map[Kind:function Name:dbInitTree] map[Kind:function Name:dbJoin] map[Kind:function Name:dbMapFileSizeToMapSize] map[Kind:function Name:dbMaxBud] map[Kind:function Name:dbMount] map[Kind:function Name:dbNextAG] map[Kind:function Name:dbReAlloc] map[Kind:function Name:dbSplit] map[Kind:function Name:dbSync] map[Kind:function Name:dbUnmount] map[Kind:function Name:dbUpdatePMap]]]
|
| 43/4 |
2026/01/27 19:00 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 16227
output: 45
thoughts: 1033
Thoughts: **Analyzing the `dbFindLeaf` Corruption and Proposed Fix**
Alright, let's dive into this. My initial thought was to look at related functions like `dbAllocDmapLev` or `dbAllocCtl`, but `dbFindLeaf` seems to be where the tree traversal logic resides. The explanation makes it clear: the code crashes because of a corrupted `tp->dmt_height`, which leads to the loop in `dbFindLeaf` descending too deep.
If `tp->dmt_height` is inflated, the loop iterates excessively. Remember, `ti` increases exponentially at each level. The existing check, `x + n >= max_size`, is meant to act as a safeguard against a corrupted height or a structural flaw within the tree.
My instinct is that changing `>` to `>=` might be the correct fix. If `x + n` exactly equals `max_size`, we return `-ENOSPC`, indicating we're at the tree's boundary, which is logical.
I've confirmed there are no other similar checks in `dbFindLeaf`, so let's apply this single change.
Wait a moment. I need to make sure this fix is applicable to both `dmaptree` and `dmapctl`. Looking at line 2952, `max_size` is determined by `is_ctl`, and the size differs depending on this boolean.
`dmtree_t` is a union and the two structures within have different sizes. If `is_ctl` is false, `max_size` is 341. If the access index is 341, it's valid memory-wise (because of the union), but logically invalid for the smaller `t1.stree` structure.
The original `>` comparison would have allowed access to index 341, because `341 > 341` would have evaluated to false. This access would be out of bounds for `t1.stree`, but technically a valid memory access in the large union. With the change, the `>=` comparison catches this edge case. The same applies for the larger `CTLTREESIZE` when `is_ctl` is true and accessing index 1365. This access is technically invalid.
Looking at the structure definitions, they are indeed a union with `s8 stree[TREESIZE]` and `s8 stree[CTLTREESIZE]` inside. Both arrays start at the same offset (16). So, accessing `t2.stree[i]` is equivalent to accessing `t1.stree[i]` for i < 341. However, for i >= 341, it would be an out-of-bounds access for `t1.stree` but a valid memory access for the compiler since it sees the full array inside of the union.
So, for `is_ctl=false`, accessing index 341 is valid C code but a logic error. For `is_ctl=true`, accessing index 1365 is a real out-of-bounds UB. The fix correctly handles both cases!
Finally, `dbFindLeaf` is declared as `static`, which means it is called only within this file and specifically by `dbFindCtl` and `dbAllocDmap`. I will now review the `dbAllocDmap` function for related issues.
|
| 44/4 |
2026/01/27 19:00 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeLines:true Name:dbAllocDmap]
Results: map[SourceCode:1995: /*
1996: * NAME: dbAllocDmap()
1997: *
1998: * FUNCTION: adjust the disk allocation map to reflect the allocation
1999: * of a specified block range within a dmap.
2000: *
2001: * this routine allocates the specified blocks from the dmap
2002: * through a call to dbAllocBits(). if the allocation of the
2003: * block range causes the maximum string of free blocks within
2004: * the dmap to change (i.e. the value of the root of the dmap's
2005: * dmtree), this routine will cause this change to be reflected
2006: * up through the appropriate levels of the dmap control pages
2007: * by a call to dbAdjCtl() for the L0 dmap control page that
2008: * covers this dmap.
2009: *
2010: * PARAMETERS:
2011: * bmp - pointer to bmap descriptor
2012: * dp - pointer to dmap to allocate the block range from.
2013: * blkno - starting block number of the block to be allocated.
2014: * nblocks - number of blocks to be allocated.
2015: *
2016: * RETURN VALUES:
2017: * 0 - success
2018: * -EIO - i/o error
2019: *
2020: * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
2021: */
2022: static int dbAllocDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
2023: int nblocks)
2024: {
2025: s8 oldroot;
2026: int rc;
2027:
2028: /* save the current value of the root (i.e. maximum free string)
2029: * of the dmap tree.
2030: */
2031: oldroot = dp->tree.stree[ROOT];
2032:
2033: /* allocate the specified (blocks) bits */
2034: dbAllocBits(bmp, dp, blkno, nblocks);
2035:
2036: /* if the root has not changed, done. */
2037: if (dp->tree.stree[ROOT] == oldroot)
2038: return (0);
2039:
2040: /* root changed. bubble the change up to the dmap control pages.
2041: * if the adjustment of the upper level control pages fails,
2042: * backout the bit allocation (thus making everything consistent).
2043: */
2044: if ((rc = dbAdjCtl(bmp, blkno, dp->tree.stree[ROOT], 1, 0)))
2045: dbFreeBits(bmp, dp, blkno, nblocks);
2046:
2047: return (rc);
2048: }
SourceFile:fs/jfs/jfs_dmap.c]
|
| 45/4 |
2026/01/27 19:00 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 18943
output: 45
thoughts: 180
Thoughts: **My Current Line of Reasoning**
Okay, so I'm tracing the data allocation process here. I've noticed `dbAllocDmap` relies on `dbAllocBits`, but I'm trying to understand the control flow related to `dbFindLeaf`. I know `dbFindLeaf` is a key function in locating the correct leaf for allocation.
Right now, I see that `dbFindCtl` explicitly calls it. Let's see... looking at the code snippet, it's pretty clear:
```c
static int dbFindCtl(struct bmap * bmp, int l2nb, int level, s64 * blkno)
{
...
rc = dbFindLeaf((dmtree_t *) & dcp->dmt_stree, l2nb, &leafidx, true);
...
}
```
Okay, so `dbFindCtl` calls `dbFindLeaf`, that makes sense. Let me think, where else do we see `dbFindCtl`? Oh, that's right, `dbAlloc` uses `dbAllocAny` which in turn calls `dbFindCtl`. Furthermore, `dbAllocAG` also calls `dbFindCtl`. This starts to create a picture in my mind, the `dbFindCtl` appears to be a central part of the allocation control path.
But, I need to know where all `dbFindLeaf` gets called. My current mental model has `is_ctl=true` on all calls to `dbFindLeaf` and I need to confirm this assumption. I'm going to search for any instances of `dbFindLeaf` in the codebase to make sure it's *always* called with `is_ctl = true`.
|
| 46/4 |
2026/01/27 19:00 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeSnippetLines:5 Name:dbFindLeaf]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:dbAllocDmapLev SourceFile:fs/jfs/jfs_dmap.c SourceLine:1969 SourceSnippet:1964:
1965: /* search the tree within the dmap page for sufficient
1966: * free space. if sufficient free space is found, dbFindLeaf()
1967: * returns the index of the leaf at which free space was found.
1968: */
1969: if (dbFindLeaf((dmtree_t *) &dp->tree, l2nb, &leafidx, false))
1970: return -ENOSPC;
1971:
1972: if (leafidx < 0)
1973: return -EIO;
1974:
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:dbFindCtl SourceFile:fs/jfs/jfs_dmap.c SourceLine:1717 SourceSnippet:1712: /* search the tree within the dmap control page for
1713: * sufficient free space. if sufficient free space is found,
1714: * dbFindLeaf() returns the index of the leaf at which
1715: * free space was found.
1716: */
1717: rc = dbFindLeaf((dmtree_t *) dcp, l2nb, &leafidx, true);
1718:
1719: /* release the buffer.
1720: */
1721: release_metapage(mp);
1722:
]] TruncatedOutput:false]
|
| 47/4 |
2026/01/27 19:00 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 20013
output: 77
thoughts: 273
Thoughts: **Analyzing the JFS Allocation Bug**
Okay, so `dbAllocDmapLev` is calling `dbFindLeaf` with `false`, indicating a dmap tree, while `dbFindCtl` calls it with `true` for a control tree. I see now that `dbFindLeaf` handles both types. The critical `if (x + n >= max_size)` check is the key here; it prevents both logical overruns, which occur in smaller trees, and the more dangerous physical buffer overruns, which is what UBSAN caught on the large tree.
The stack trace clarifies the call path: `dbFindLeaf` is called by `dbFindCtl`, which in turn is called from `dbAllocAny`, then `dbAlloc`, leading to `diNewIAG`, and so on. The crash specifically occurs when `is_ctl` is `true`, and I've confirmed that `max_size` is 1365 in this scenario.
Therefore, this confirms my suspicion. The fix is a simple off-by-one error: The condition should be `>=` rather than `>`.
I'll apply this patch directly using `codeeditor`:
```c
fs/jfs/jfs_dmap.c:
2974: if (x + n > max_size)
2975: return -ENOSPC;
```
becomes
```c
2974: if (x + n >= max_size)
2975: return -ENOSPC;
```
|
| 48/4 |
2026/01/27 19:00 |
tool |
codeeditor |
0m
Args: map[CurrentCode: if (x + n > max_size)
return -ENOSPC; NewCode: if (x + n >= max_size)
return -ENOSPC; SourceFile:fs/jfs/jfs_dmap.c]
Results:
|
| 49/4 |
2026/01/27 19:00 |
llm |
patch-generator |
0m
Model:
Tokens:
input: 20706
output: 337
thoughts: 1834
Thoughts: **Fix Verification and Boundary Condition Analysis**
Okay, I've applied the fix, and now it's time to thoroughly verify its correctness. The core issue was an off-by-one error, where `x + n` could reach `max_size` (which is 1365), leading to an out-of-bounds access on a zero-based array. The problem stemmed from potential corruption of `tp->dmt_height`, causing the loop to iterate excessively.
The fix, which now uses `>=` instead of `>`, directly prevents array access when `x + n` equals `max_size`. I need to ensure this fully addresses all boundary cases.
Let's break down the variables. `n` ranges from 0 to 3, and `x` is represented by `ti`. `ti` itself depends on previous values of `ti` and `n`. I have to confirm that `x+n` can not "jump" over the `max_size` due to how those variables are calculated.
I understand that `ti` grows roughly x4. Also, `max_size` is roughly `4^(height+1)/3`. Let's consider scenarios. If `x` starts extremely large, then `x+n` can be large.
If `x` is right below `max_size`, let's say `max_size-1`. Then, `x+n` (n=0) is fine. But `x+n` (n=1) becomes `max_size`. The original `>` check would fail (false), and the code would incorrectly try to access `stree[max_size]` leading to a crash. However, with the new `>=` check, it correctly succeeds (true) and returns `-ENOSPC`, which is the intended behavior.
The `x + n >= max_size` condition now covers this boundary case. What if `x` itself starts large, because of a previous bad iteration? In the previous iteration, `ti` was calculated. `ti` is calculated as `((ti + n) << 2) + 1`. If `ti` was already large (i.e., invalid), the next `ti` will become even larger. If `ti` was invalid (equals `max_size`), then `x` is `max_size`. In the next iteration, `x+0` is `max_size`, which is correct. The new check correctly handles these cases.
The key is that `x+n` can be *exactly* `max_size`. I considered that and made sure this is taken care of. What about `x+n` being `max_size + 1`? The `>` check would catch it. The only missing case was equality.
Next, I need to evaluate the comparison logic: `l2nb <= tp->dmt_stree[x + n]`. `l2nb` is an `int`, while `dmt_stree` is an `s8` array. However, the values in `dmt_stree` represent log2 of free blocks, so they're small integers. `l2nb` is also expected to be small. This comparison should be fine, and no issues are anticipated here.
Now I am confident that the solution addresses the root cause of the crash.
I also need to remember the `is_ctl` parameter. When `is_ctl` is `true`, we're dealing with `CTLTREESIZE` which applies to a `dmapctl` struct. The `dmapctl` has `stree[CTLTREESIZE]`. Conversely, when `is_ctl` is `false`, we use `TREESIZE`, which is associated with a `dmaptree` struct which means the `t2.stree` union member is accessed. `dbFindLeaf` is called with `is_ctl=false`, `tp` is cast to `dmtree_t*`, and `tp->dmt_stree` accesses `tp->t2.stree`. With type-punning, if the underlying object is a `dmaptree`, and you accessed `t2.stree[i]` where `i >= TREESIZE` (341), you'd be accessing memory beyond the `dmaptree` if the underlying object is a `dmaptree`. But remember that padding exists. With a `dmap` struct where there's padding after `tree`, accessing `tree.stree` up to index 340 is the valid part of `dmaptree`. If `is_ctl=false` you're really accessing the padding. This is safe, and `max_size` is set to `TREESIZE
|
| 50/3 |
2026/01/27 19:01 |
action |
test-patch |
9m
Results: map[PatchDiff:diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cdfa699cd..18a7dc58f 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2971,7 +2971,7 @@ static int dbFindLeaf(dmtree_t *tp, int l2nb, int *leafidx, bool is_ctl)
/* sufficient free space found. move to the next
* level (or quit if this is the last level).
*/
- if (x + n > max_size)
+ if (x + n >= max_size)
return -ENOSPC;
if (l2nb <= tp->dmt_stree[x + n])
break;
TestError:]
|
| 51/1 |
2026/01/27 19:11 |
agent |
description-generator |
0m
Model:
Instruction:
You are an experienced Linux kernel developer tasked with writing a commit description for
a kernel bug fixing commit. The description should start with a one-line summary,
and then include description of the bug being fixed, and how it's fixed by the provided patch.
Your final reply should contain only the text of the commit description.
Phrase the one-line summary so that it is not longer than 72 characters.
The rest of the description must be word-wrapped at 72 characters.
Prefer calling several tools at the same time to save round-trips.
Prompt:
The crash that corresponds to the bug is:
------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in /usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/5452af61ab2e1f5601403fe379188fc9d8a831af/fs/jfs/jfs_dmap.c:2976:16
index 1365 is out of range for type 's8[1365]' (aka 'signed char[1365]')
CPU: 1 UID: 0 PID: 6199 Comm: syz-executor257 Not tainted syzkaller #1 PREEMPT_{RT,(full)}
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x10e/0x190 lib/dump_stack.c:120
ubsan_epilogue lib/ubsan.c:233 [inline]
__ubsan_handle_out_of_bounds+0x115/0x140 lib/ubsan.c:455
dbFindLeaf+0x308/0x520 fs/jfs/jfs_dmap.c:2976
dbFindCtl+0x267/0x520 fs/jfs/jfs_dmap.c:1717
dbAllocAny fs/jfs/jfs_dmap.c:1527 [inline]
dbAlloc+0x5fd/0xba0 fs/jfs/jfs_dmap.c:878
diNewIAG fs/jfs/jfs_imap.c:2510 [inline]
diAllocExt fs/jfs/jfs_imap.c:1905 [inline]
diAllocAG+0xcf0/0x1db0 fs/jfs/jfs_imap.c:1669
diAlloc+0x1d4/0x1670 fs/jfs/jfs_imap.c:1590
ialloc+0x8c/0x8f0 fs/jfs/jfs_inode.c:56
jfs_mkdir+0x193/0xa70 fs/jfs/namei.c:225
vfs_mkdir+0x530/0x5d0 fs/namei.c:5139
do_mkdirat+0x27a/0x4b0 fs/namei.c:5173
__do_sys_mkdir fs/namei.c:5200 [inline]
__se_sys_mkdir fs/namei.c:5198 [inline]
__x64_sys_mkdir+0x6c/0x80 fs/namei.c:5198
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe8/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc490daf897
Code: 1f 40 00 48 89 f2 b9 00 01 00 00 48 89 fe bf 9c ff ff ff e9 7b 37 03 00 66 2e 0f 1f 84 00 00 00 00 00 90 b8 53 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d0 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fc490d51038 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 0000200000000200 RCX: 00007fc490daf897
RDX: 0000000002b1247d RSI: 00000000000001ff RDI: 00002000000002c0
RBP: 0000000000000000 R08: 00000000000000fc R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 00002000000002c0
R13: 00007fc490d510d0 R14: 0000000000000000 R15: 0000000000000000
</TASK>
---[ end trace ]---
The explanation of the root cause of the bug is:
The root cause of this crash is an off-by-one error in the bounds check within the `dbFindLeaf` function in `fs/jfs/jfs_dmap.c`.
The function `dbFindLeaf` iterates through the levels of a dmap tree to find a leaf with sufficient free blocks. The number of iterations is determined by `tp->dmt_height`, which is read from the filesystem image (disk). The crash occurs when `tp->dmt_height` is corrupted (too large), causing the loop to descend deeper than the defined tree structure allows, resulting in the calculated index `x + n` exceeding the valid range of the `tp->dmt_stree` array.
Specifically:
1. The array `tp->dmt_stree` has a size of `CTLTREESIZE` (1365) when `is_ctl` is true (which is the case in the stack trace, called from `dbFindCtl`). The valid indices are `0` to `1364`.
2. The code includes a bounds check at line 2974: `if (x + n > max_size)`.
3. `max_size` is set to `CTLTREESIZE` (1365).
4. When `x + n` reaches `1365`, the condition `1365 > 1365` evaluates to false, allowing execution to proceed.
5. The code then attempts to access `tp->dmt_stree[1365]` at line 2976, triggering the UBSAN array-index-out-of-bounds error.
The bounds check should use `>=` instead of `>` to correctly handle the case where the index equals the array size.
**Fix:**
Change the bounds check in `fs/jfs/jfs_dmap.c` from:
```c
if (x + n > max_size)
```
to:
```c
if (x + n >= max_size)
```
The diff of the bug fix is:
diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cdfa699cd..18a7dc58f 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2971,7 +2971,7 @@ static int dbFindLeaf(dmtree_t *tp, int l2nb, int *leafidx, bool is_ctl)
/* sufficient free space found. move to the next
* level (or quit if this is the last level).
*/
- if (x + n > max_size)
+ if (x + n >= max_size)
return -ENOSPC;
if (l2nb <= tp->dmt_stree[x + n])
break;
Additional description of the patch:
The bug is an off-by-one error in the `dbFindLeaf` function in `fs/jfs/jfs_dmap.c`.
The code iterates over a dmap tree to find free blocks. The loop calculates an index `x + n` into the `tp->dmt_stree` array. The bounds check `if (x + n > max_size)` allows the index to be equal to `max_size`.
Since `max_size` represents the size of the array (e.g., 1365 for `CTLTREESIZE`), and arrays are 0-indexed, an index of `max_size` is out of bounds. The valid indices are `0` to `max_size - 1`.
The crash report shows UBSAN detecting an access at index 1365 for an array of size 1365.
This happens when `tp->dmt_height` is corrupted (too large), causing the loop to go deeper than expected and the index to grow beyond the tree size.
The fix is to change the condition to `if (x + n >= max_size)` to ensure the index stays within valid bounds `[0, max_size - 1]`.
The patch modifies `fs/jfs/jfs_dmap.c`:
```c
<<<<
if (x + n > max_size)
return -ENOSPC;
====
if (x + n >= max_size)
return -ENOSPC;
>>>>
```
Reply: jfs: fix array-index-out-of-bounds in dbFindLeaf
Syzkaller reported the following UBSAN array-index-out-of-bounds issue in
dbFindLeaf:
UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:2976:16
index 1365 is out of range for type 's8[1365]' (aka 'signed char[1365]')
...
dbFindLeaf+0x308/0x520 fs/jfs/jfs_dmap.c:2976
dbFindCtl+0x267/0x520 fs/jfs/jfs_dmap.c:1717
...
The function dbFindLeaf() iterates through the dmap tree to find a leaf
with sufficient free blocks. The code calculates an index `x + n` into
the `tp->dmt_stree` array. The bounds check `if (x + n > max_size)`
fails to catch the case where `x + n` equals `max_size`.
When `is_ctl` is true, `max_size` is set to `CTLTREESIZE` (1365). If
`x + n` becomes 1365, the check passes, and the code accesses
`tp->dmt_stree[1365]`, which is out of bounds. This can happen if
`tp->dmt_height` is corrupted (too large), causing the loop to descend
deeper than expected.
Fix this by using `>=` in the bounds check to ensure the index is within
the valid range [0, max_size - 1].
|
| 52/2 |
2026/01/27 19:11 |
llm |
description-generator |
0m
Model:
Tokens:
input: 4502
output: 44
thoughts: 396
Thoughts: **Kernel Bug Fix Commit Message Thoughts**
Okay, so I need to craft a concise and accurate commit message for this kernel bug fix. I've got all the essentials: the crash report, the root cause analysis, the fix itself, and the patch diff. It's a UBSAN array-index-out-of-bounds error, specifically in the JFS filesystem, within the `dbFindLeaf` function in `fs/jfs/jfs_dmap.c`.
The crash report pinpoints the exact line: `fs/jfs/jfs_dmap.c:2976`. The error is very clear; index 1365 is out of bounds for an array of size 1365. That off-by-one error, from my understanding of the root cause, is due to the faulty `if (x + n > max_size)` check, where `max_size` is 1365. The calculation `x + n` results in 1365, which doesn't trigger the "out of bounds" condition. The fix is straightforward: change that to `>=`.
Now, the commit message. I think a good summary line would be something along the lines of "`jfs: fix array-index-out-of-bounds in dbFindLeaf`" or "`jfs: fix ubsan array-index-out-of-bounds in dbFindLeaf`", which is concise and descriptive.
The commit description needs to clarify the issue: that a potentially corrupted `tp->dmt_height` can result in a loop calculation that generates an invalid index. The current check, using `>`, is insufficient because it permits access to the array's "end" element, which is still out of bounds. Replacing it with `>=` will provide the necessary bound protection.
Just to be absolutely certain, I'm going to run a quick `codesearch-definition-source` check on the surrounding code, especially around `CTLTREESIZE` and `max_size`. Although the problem seems clear based on the crash report and the code context, a quick verification never hurts, and it will give me the added context that I can use in the commit's description. The file is, again, `fs/jfs/jfs_dmap.c`, and the function is `dbFindLeaf`.
|
| 53/2 |
2026/01/27 19:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/jfs/jfs_dmap.c IncludeLines:true Name:dbFindLeaf]
Results: map[SourceCode:2924: /*
2925: * NAME: dbFindLeaf()
2926: *
2927: * FUNCTION: search a dmtree_t for sufficient free blocks, returning
2928: * the index of a leaf describing the free blocks if
2929: * sufficient free blocks are found.
2930: *
2931: * the search starts at the top of the dmtree_t tree and
2932: * proceeds down the tree to the leftmost leaf with sufficient
2933: * free space.
2934: *
2935: * PARAMETERS:
2936: * tp - pointer to the tree to be searched.
2937: * l2nb - log2 number of free blocks to search for.
2938: * leafidx - return pointer to be set to the index of the leaf
2939: * describing at least l2nb free blocks if sufficient
2940: * free blocks are found.
2941: * is_ctl - determines if the tree is of type ctl
2942: *
2943: * RETURN VALUES:
2944: * 0 - success
2945: * -ENOSPC - insufficient free blocks.
2946: */
2947: static int dbFindLeaf(dmtree_t *tp, int l2nb, int *leafidx, bool is_ctl)
2948: {
2949: int ti, n = 0, k, x = 0;
2950: int max_size, max_idx;
2951:
2952: max_size = is_ctl ? CTLTREESIZE : TREESIZE;
2953: max_idx = is_ctl ? LPERCTL : LPERDMAP;
2954:
2955: /* first check the root of the tree to see if there is
2956: * sufficient free space.
2957: */
2958: if (l2nb > tp->dmt_stree[ROOT])
2959: return -ENOSPC;
2960:
2961: /* sufficient free space available. now search down the tree
2962: * starting at the next level for the leftmost leaf that
2963: * describes sufficient free space.
2964: */
2965: for (k = le32_to_cpu(tp->dmt_height), ti = 1;
2966: k > 0; k--, ti = ((ti + n) << 2) + 1) {
2967: /* search the four nodes at this level, starting from
2968: * the left.
2969: */
2970: for (x = ti, n = 0; n < 4; n++) {
2971: /* sufficient free space found. move to the next
2972: * level (or quit if this is the last level).
2973: */
2974: if (x + n > max_size)
2975: return -ENOSPC;
2976: if (l2nb <= tp->dmt_stree[x + n])
2977: break;
2978: }
2979:
2980: /* better have found something since the higher
2981: * levels of the tree said it was here.
2982: */
2983: assert(n < 4);
2984: }
2985: if (le32_to_cpu(tp->dmt_leafidx) >= max_idx)
2986: return -ENOSPC;
2987:
2988: /* set the return to the leftmost leaf describing sufficient
2989: * free space.
2990: */
2991: *leafidx = x + n - le32_to_cpu(tp->dmt_leafidx);
2992:
2993: return (0);
2994: }
SourceFile:fs/jfs/jfs_dmap.c]
|
| 54/2 |
2026/01/27 19:11 |
llm |
description-generator |
0m
Model:
Tokens:
input: 6574
output: 401
thoughts: 1419
Thoughts: **Analyzing and Fixing the Array-Index-Out-of-Bounds in `dbFindLeaf`**
Okay, the code confirms the issue. I see it: line 2952 sets `max_size`, line 2970 has a loop from `n = 0` to 3, and then on line 2974, we have the crucial bound check: `if (x + n > max_size)`. Line 2976 is where the access to `tp->dmt_stree[x + n]` happens. The problem is clear: if `x + n` *equals* `max_size`, the condition is false (`max_size` is not *greater* than `max_size`), and the OOB access happens. The UBSAN report confirms it, hitting `s8[1365]` at index 1365. `CTLTREESIZE` from the report corresponds to 1365.
The fix is straightforward; it's a classic off-by-one. We need to change the condition to `>=`. That will fix the comparison for valid indices.
Now, I need to craft a good commit message. Let's see...
I'll structure it like this: A one-line summary followed by the detailed body.
**Here's the commit message I'll write:**
Summary: jfs: fix array-index-out-of-bounds in dbFindLeaf
Body:
Syzkaller reported the following UBSAN array-index-out-of-bounds issue in dbFindLeaf:
UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:2976:16
index 1365 is out of range for type 's8[1365]' (aka 'signed char[1365]')
...
dbFindLeaf+0x308/0x520 fs/jfs/jfs_dmap.c:2976
dbFindCtl+0x267/0x520 fs/jfs/jfs_dmap.c:1717
...
The function dbFindLeaf() iterates through the dmap tree to find a leaf with sufficient free blocks. The code calculates an index `x + n` into the `tp->dmt_stree` array. The bounds check `if (x + n > max_size)` fails to catch the case where `x + n` equals `max_size`.
When `is_ctl` is true, `max_size` is set to `CTLTREESIZE` (1365). If `x + n` becomes 1365, the check passes, and the code accesses `tp->dmt_stree[1365]`, which is out of bounds. This can happen if `tp->dmt_height` is corrupted (too large).
Fix this by using `>=` in the bounds check to ensure the index is within valid range [0, max_size - 1].
I'm ready to push it! The key is that the description focuses on the bug *and* the reason it occurs. The check that currently used `>` is too weak, and the fix is to use `>=`. The corruption scenario is important - `dmt_height` being too large coming from disk is a good "corrupted image" case for syzkaller to find. The description should be comprehensive. I'll make sure `max_size` matches the array size. UBSAN states `s8[1365]`, and the message is pretty clear, but I will check the header file. All should be good!
|