| 0/0 |
2026/08/09 04:33 |
flow |
assessment-security |
2m
Results: map[DenialOfService:true Explanation:**Bug Analysis:**
The bug is a NULL pointer dereference in `strcmp()` called from
`remove_cache_mod()` in `kernel/trace/trace_events.c`.
It is triggered via the ftrace `set_event` interface. When a user writes a
wildcard module event filter (e.g., `*:mod:foo`) to the `set_event` file, the
kernel caches this filter using `cache_mod()`. Because of the wildcard `*`, the
`match` string is passed as `NULL`, resulting in an `event_mod` entry where
`event_mod->match` is `NULL`.
Subsequently, if the user writes a specific event filter to remove it (e.g.,
`!bar:mod:foo`), `remove_cache_mod()` is invoked. This function iterates over
the cached module events and attempts to compare the new match string (`"bar"`)
with the cached one using `strcmp(event_mod->match, match)`. Since
`event_mod->match` is `NULL`, this results in a NULL pointer dereference.
**Security Impact:**
* **Exploitable:** No. The bug is a simple read from a NULL pointer (or its
KASAN shadow equivalent). It does not provide any primitives for memory
corruption, arbitrary execution, or information leaks.
* **Denial Of Service:** Yes. Triggering the bug causes a kernel oops. Even if
`panic_on_oops` is not set, the process will be killed while holding the global
`event_mutex`. This leaves the mutex permanently locked, deadlocking any future
attempts to use or configure ftrace on the system.
* **Accessible From Unprivileged Processes:** No. The bug is triggered by
writing to the `set_event` file in `tracefs` (usually mounted at
`/sys/kernel/tracing` or `/sys/kernel/debug/tracing`). By default, these files
have `0640` permissions and are owned by root, meaning unprivileged users cannot
access them.
* **Accessible From User Namespaces:** No. The `tracefs` and `debugfs`
filesystems do not have the `FS_USERNS_MOUNT` flag set. Therefore, they cannot
be mounted by an unprivileged user inside a user namespace.
* **Other Triggers:** The bug is strictly tied to the ftrace configuration
interface and cannot be triggered via network traffic, malicious filesystems,
peripherals, or VM guest interactions. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/08/09 04:33 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/08/09 04:33 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/app/workdir/cache/src/c47bee79b7c1491a9e684c5a8653382995c504b0]
|
| 3/1 |
2026/08/09 04:33 |
action |
kernel-builder |
0m
Results: map[KernelObj:/app/workdir/cache/build/4c1dac6389458ee2dc4aa62375fe3e74a55b1dcc]
|
| 4/1 |
2026/08/09 04:33 |
action |
codesearch-prepare |
0m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/08/09 04:33 |
agent |
expert |
2m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Instruction: You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by grepping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption, elevated privileges, or an information leak.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completely wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control transfers, that also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitability depends on how exactly the uninit value
is used in the code, and what it affects.
Information leaks are exploitable on their own and should be classified as such. A bug that copies kernel
memory contents to userspace (e.g. an out-of-bounds read whose result is returned to the caller, or
uninitialized stack/heap bytes written to a user buffer) is exploitable: it can reveal kernel pointer
values and defeat KASLR, expose sensitive data such as cryptographic keys or other processes' memory, and
serves as a necessary building block in most modern kernel privilege-escalation exploit chains. Do not classify
an information leak as non-exploitable solely because it does not directly cause a memory write or control-flow
hijack; the leak itself is the exploit primitive.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidential Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
Unable to handle kernel paging request at virtual address dfff800000000000
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
Mem abort info:
ESR = 0x0000000096000005
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x05: level 1 translation fault
Data abort info:
ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0
[dfff800000000000] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] SMP
Modules linked in:
CPU: 1 UID: 0 PID: 14446 Comm: syz.3.4021 Tainted: G L syzkaller #0 PREEMPT
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : strcmp+0x28/0xf0 lib/string.c:265
lr : remove_cache_mod kernel/trace/trace_events.c:948 [inline]
lr : cache_mod kernel/trace/trace_events.c:977 [inline]
lr : __ftrace_set_clr_event_nolock+0x6a0/0x940 kernel/trace/trace_events.c:1395
sp : ffff800093a67840
x29: ffff800093a67870 x28: dfff800000000000 x27: 0000000000000000
x26: ffff800088d6e8b0 x25: ffff0000c50e1100 x24: 00000000ffffffea
x23: ffff800088d6e8b0 x22: 0000000000000000 x21: dfff800000000000
x20: ffff0000c50e1118 x19: ffff0000c84e7b80 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000001
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: dfff800000000000 x9 : ffff0000d554ef01
x8 : 0000000000000000 x7 : ffff800080538ea0 x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff8000806c6790
x2 : 0000000000000000 x1 : ffff0000d554ef01 x0 : 0000000000000000
Call trace:
strcmp+0x28/0xf0 lib/string.c:265 (P)
remove_cache_mod kernel/trace/trace_events.c:948 [inline]
cache_mod kernel/trace/trace_events.c:977 [inline]
__ftrace_set_clr_event_nolock+0x6a0/0x940 kernel/trace/trace_events.c:1395
__ftrace_set_clr_event+0xa8/0xec kernel/trace/trace_events.c:1410
ftrace_set_clr_event+0x2a0/0x438 kernel/trace/trace_events.c:1460
ftrace_event_write+0x1dc/0x28c kernel/trace/trace_events.c:1548
vfs_write+0x2a4/0xa0c fs/read_write.c:685
ksys_write+0x12c/0x228 fs/read_write.c:739
__do_sys_write fs/read_write.c:750 [inline]
__se_sys_write fs/read_write.c:747 [inline]
__arm64_sys_write+0x84/0x98 fs/read_write.c:747
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:738
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:757
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590
Code: aa0103e9 f2fbffea d343fc0b 1200080c (38ea696b)
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
0: aa0103e9 mov x9, x1
4: f2fbffea movk x10, #0xdfff, lsl #48
8: d343fc0b lsr x11, x0, #3
c: 1200080c and w12, w0, #0x7
* 10: 38ea696b ldrsb w11, [x11, x10] <-- trapping instruction
Reply: **Bug Analysis:**
The bug is a NULL pointer dereference in `strcmp()` called from `remove_cache_mod()` in `kernel/trace/trace_events.c`.
It is triggered via the ftrace `set_event` interface. When a user writes a wildcard module event filter (e.g., `*:mod:foo`) to the `set_event` file, the kernel caches this filter using `cache_mod()`. Because of the wildcard `*`, the `match` string is passed as `NULL`, resulting in an `event_mod` entry where `event_mod->match` is `NULL`.
Subsequently, if the user writes a specific event filter to remove it (e.g., `!bar:mod:foo`), `remove_cache_mod()` is invoked. This function iterates over the cached module events and attempts to compare the new match string (`"bar"`) with the cached one using `strcmp(event_mod->match, match)`. Since `event_mod->match` is `NULL`, this results in a NULL pointer dereference.
**Security Impact:**
* **Exploitable:** No. The bug is a simple read from a NULL pointer (or its KASAN shadow equivalent). It does not provide any primitives for memory corruption, arbitrary execution, or information leaks.
* **Denial Of Service:** Yes. Triggering the bug causes a kernel oops. Even if `panic_on_oops` is not set, the process will be killed while holding the global `event_mutex`. This leaves the mutex permanently locked, deadlocking any future attempts to use or configure ftrace on the system.
* **Accessible From Unprivileged Processes:** No. The bug is triggered by writing to the `set_event` file in `tracefs` (usually mounted at `/sys/kernel/tracing` or `/sys/kernel/debug/tracing`). By default, these files have `0640` permissions and are owned by root, meaning unprivileged users cannot access them.
* **Accessible From User Namespaces:** No. The `tracefs` and `debugfs` filesystems do not have the `FS_USERNS_MOUNT` flag set. Therefore, they cannot be mounted by an unprivileged user inside a user namespace.
* **Other Triggers:** The bug is strictly tied to the ftrace configuration interface and cannot be triggered via network traffic, malicious filesystems, peripherals, or VM guest interactions.
|
| 6/2 |
2026/08/09 04:33 |
llm |
expert |
0m
Model:
Tokens:
input: 7631
output: 38
thoughts: 185
Thoughts: **Analyzing a Kernel Null-Pointer Dereference**
Okay, so I've got a kernel bug report here. It looks like we've got a KASAN null-pointer dereference β always a fun one. The report highlights an issue in the range [0x0000000000000000-0x0000000000000007]. That's the tell-tale sign, right? The PC is `strcmp+0x28/0xf0` in `lib/string.c`, specifically line 265. That, by itself, isn't the root cause but it's where the crash happens. Let's look at the backtrace. The return address traces up through `remove_cache_mod`, and then `cache_mod`, both of which look like they're inlined calls within `kernel/trace/trace_events.c`. The ultimate culprit appears to be `__ftrace_set_clr_event_nolock` at `kernel/trace/trace_events.c:1395`. Given the context and the functions involved, I'm betting this is a classic race condition in the tracing code, probably related to modifying the cache while another operation is trying to read or write to it. I'll need to dig into `kernel/trace/trace_events.c` and figure out precisely how these functions interact and where the lock is, or isn't, being correctly handled. The fact that `strcmp` is involved suggests a string comparison is failing, likely on a null pointer. Time to get the debugger out!
|
| 7/2 |
2026/08/09 04:33 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:remove_cache_mod]
Results: map[SourceCode: 938: static int remove_cache_mod(struct trace_array *tr, const char *mod,
939: const char *match, const char *system, const char *event)
940: {
941: struct event_mod_load *event_mod, *n;
942: int ret = -EINVAL;
943:
944: list_for_each_entry_safe(event_mod, n, &tr->mod_events, list) {
945: if (strcmp(event_mod->module, mod) != 0)
946: continue;
947:
948: if (match && strcmp(event_mod->match, match) != 0)
949: continue;
950:
951: if (system &&
952: (!event_mod->system || strcmp(event_mod->system, system) != 0))
953: continue;
954:
955: if (event &&
956: (!event_mod->event || strcmp(event_mod->event, event) != 0))
957: continue;
958:
959: free_event_mod(event_mod);
960: ret = 0;
961: }
962:
963: return ret;
964: }
SourceFile:kernel/trace/trace_events.c]
|
| 8/2 |
2026/08/09 04:33 |
llm |
expert |
0m
Model:
Tokens:
input: 8627
output: 53
thoughts: 66
Thoughts: **Debugging a String Comparison**
Okay, so I'm hitting a crash in the `strcmp` call. The interesting thing is that the `match` variable isn't NULL, that's already been checked. Therefore, the problem *must* be with `event_mod->match` being NULL. Time to trace back and find out where that field is populated and, crucially, how it's being set to NULL in the first place. This is a classic null pointer dereference, and I need to track down the root cause. Let's dig into the code and see where `event_mod->match` gets its value.
|
| 9/2 |
2026/08/09 04:33 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:5 Name:event_mod_load::match SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:writes ReferencingEntityKind:function ReferencingEntityName:cache_mod SourceFile:kernel/trace/trace_events.c SourceLine:989 SourceSnippet: 984: event_mod->module = kstrdup(mod, GFP_KERNEL);
985: if (!event_mod->module)
986: goto out_free;
987:
988: if (match) {
989: event_mod->match = kstrdup(match, GFP_KERNEL);
990: if (!event_mod->match)
991: goto out_free;
992: }
993:
994: if (system) {
] map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:cache_mod SourceFile:kernel/trace/trace_events.c SourceLine:990 SourceSnippet: 985: if (!event_mod->module)
986: goto out_free;
987:
988: if (match) {
989: event_mod->match = kstrdup(match, GFP_KERNEL);
990: if (!event_mod->match)
991: goto out_free;
992: }
993:
994: if (system) {
995: event_mod->system = kstrdup(system, GFP_KERNEL);
] map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:free_event_mod SourceFile:kernel/trace/trace_events.c SourceLine:923 SourceSnippet: 919: static void free_event_mod(struct event_mod_load *event_mod)
920: {
921: list_del(&event_mod->list);
922: kfree(event_mod->module);
923: kfree(event_mod->match);
924: kfree(event_mod->system);
925: kfree(event_mod->event);
926: kfree(event_mod);
927: }
] map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:remove_cache_mod SourceFile:kernel/trace/trace_events.c SourceLine:948 SourceSnippet: 943:
944: list_for_each_entry_safe(event_mod, n, &tr->mod_events, list) {
945: if (strcmp(event_mod->module, mod) != 0)
946: continue;
947:
948: if (match && strcmp(event_mod->match, match) != 0)
949: continue;
950:
951: if (system &&
952: (!event_mod->system || strcmp(event_mod->system, system) != 0))
953: continue;
] map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:s_show SourceFile:kernel/trace/trace_events.c SourceLine:1778 SourceSnippet:1773:
1774: if (iter->type == SET_EVENT_FILE)
1775: return t_show(m, iter->file);
1776:
1777: /* When match is set, system and event are not */
1778: if (iter->event_mod->match) {
1779: seq_printf(m, "%s:mod:%s\n", iter->event_mod->match,
1780: iter->event_mod->module);
1781: return 0;
1782: }
1783:
] map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:s_show SourceFile:kernel/trace/trace_events.c SourceLine:1779 SourceSnippet:1774: if (iter->type == SET_EVENT_FILE)
1775: return t_show(m, iter->file);
1776:
1777: /* When match is set, system and event are not */
1778: if (iter->event_mod->match) {
1779: seq_printf(m, "%s:mod:%s\n", iter->event_mod->match,
1780: iter->event_mod->module);
1781: return 0;
1782: }
1783:
1784: system = iter->event_mod->system ? : "*";
] map[ReferenceKind:reads ReferencingEntityKind:function ReferencingEntityName:update_mod_cache SourceFile:kernel/trace/trace_events.c SourceLine:3903 SourceSnippet:3898:
3899: list_for_each_entry_safe(event_mod, n, &tr->mod_events, list) {
3900: if (strcmp(event_mod->module, mod->name) != 0)
3901: continue;
3902:
3903: __ftrace_set_clr_event_nolock(tr, event_mod->match,
3904: event_mod->system,
3905: event_mod->event, 1, mod->name);
3906: free_event_mod(event_mod);
3907: }
3908: }
]] TruncatedOutput:false]
|
| 10/2 |
2026/08/09 04:33 |
llm |
expert |
0m
Model:
Tokens:
input: 10398
output: 36
thoughts: 37
Thoughts: Okay, let's see. Here's my understanding, as if these were my thoughts:
**Analyzing Potential Null Pointer Dereference**
Right, so I'm looking at this code and it seems like `event_mod->match` could potentially be NULL. I need to figure out why. Aha! It looks like if the `match` argument passed to `cache_mod` was NULL, then `event_mod->match` would also be NULL. Okay, so `cache_mod` is the critical point here. I need to take a closer look at that function to confirm this, and understand the implications.
|
| 11/2 |
2026/08/09 04:33 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:cache_mod]
Results: map[SourceCode: 966: static int cache_mod(struct trace_array *tr, const char *mod, int set,
967: const char *match, const char *system, const char *event)
968: {
969: struct event_mod_load *event_mod;
970:
971: /* If the module exists, then this just failed to find an event */
972: if (module_exists(mod))
973: return -EINVAL;
974:
975: /* See if this is to remove a cached filter */
976: if (!set)
977: return remove_cache_mod(tr, mod, match, system, event);
978:
979: event_mod = kzalloc_obj(*event_mod);
980: if (!event_mod)
981: return -ENOMEM;
982:
983: INIT_LIST_HEAD(&event_mod->list);
984: event_mod->module = kstrdup(mod, GFP_KERNEL);
985: if (!event_mod->module)
986: goto out_free;
987:
988: if (match) {
989: event_mod->match = kstrdup(match, GFP_KERNEL);
990: if (!event_mod->match)
991: goto out_free;
992: }
993:
994: if (system) {
995: event_mod->system = kstrdup(system, GFP_KERNEL);
996: if (!event_mod->system)
997: goto out_free;
998: }
999:
1000: if (event) {
1001: event_mod->event = kstrdup(event, GFP_KERNEL);
1002: if (!event_mod->event)
1003: goto out_free;
1004: }
1005:
1006: list_add(&event_mod->list, &tr->mod_events);
1007:
1008: return 0;
1009:
1010: out_free:
1011: free_event_mod(event_mod);
1012:
1013: return -ENOMEM;
1014: }
SourceFile:kernel/trace/trace_events.c]
|
| 12/2 |
2026/08/09 04:33 |
llm |
expert |
0m
Model:
Tokens:
input: 11295
output: 45
thoughts: 42
Thoughts: Here's my take on the thought process, as requested:
**Deconstructing the Call Stack**
Okay, so I'm looking at this code and immediately I see `cache_mod` is called from `__ftrace_set_clr_event_nolock`. That's the key. I need to understand what `__ftrace_set_clr_event_nolock` is doing and what its inputs are. The relationship between `cache_mod` and this function is central to whatever this code is trying to accomplish. Let's dig into `__ftrace_set_clr_event_nolock` and see if the function's internals provide any clues as to why `cache_mod` is being called in the first place. This probably has to do with how the events in Ftrace get changed or modified and how this modification interacts with the cache.
|
| 13/2 |
2026/08/09 04:34 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:__ftrace_set_clr_event_nolock]
Results: map[SourceCode:1321: /*
1322: * __ftrace_set_clr_event(NULL, NULL, NULL, set) will set/unset all events.
1323: */
1324: static int
1325: __ftrace_set_clr_event_nolock(struct trace_array *tr, const char *match,
1326: const char *sub, const char *event, int set,
1327: const char *mod)
1328: {
1329: struct trace_event_file *file;
1330: struct trace_event_call *call;
1331: char *module __free(kfree) = NULL;
1332: const char *name;
1333: int ret = -EINVAL;
1334: int eret = 0;
1335:
1336: if (mod) {
1337: char *p;
1338:
1339: module = kstrdup(mod, GFP_KERNEL);
1340: if (!module)
1341: return -ENOMEM;
1342:
1343: /* Replace all '-' with '_' as that's what modules do */
1344: for (p = strchr(module, '-'); p; p = strchr(p + 1, '-'))
1345: *p = '_';
1346: }
1347:
1348: list_for_each_entry(file, &tr->events, list) {
1349:
1350: call = file->event_call;
1351:
1352: /* If a module is specified, skip events that are not that module */
1353: if (module &&
1354: ((call->flags & TRACE_EVENT_FL_DYNAMIC) ||
1355: !call->module || strcmp(module_name(call->module), module)))
1356: continue;
1357:
1358: name = trace_event_name(call);
1359:
1360: if (!name || !call->class || !call->class->reg)
1361: continue;
1362:
1363: if (call->flags & TRACE_EVENT_FL_IGNORE_ENABLE)
1364: continue;
1365:
1366: if (match &&
1367: strcmp(match, name) != 0 &&
1368: strcmp(match, call->class->system) != 0)
1369: continue;
1370:
1371: if (sub && strcmp(sub, call->class->system) != 0)
1372: continue;
1373:
1374: if (event && strcmp(event, name) != 0)
1375: continue;
1376:
1377: ret = ftrace_event_enable_disable(file, set);
1378:
1379: /*
1380: * Save the first error and return that. Some events
1381: * may still have been enabled, but let the user
1382: * know that something went wrong.
1383: */
1384: if (ret && !eret)
1385: eret = ret;
1386:
1387: ret = eret;
1388: }
1389:
1390: /*
1391: * If this is a module setting and nothing was found,
1392: * check if the module was loaded. If it wasn't cache it.
1393: */
1394: if (module && ret == -EINVAL && !eret)
1395: ret = cache_mod(tr, module, set, match, sub, event);
1396:
1397: return ret;
1398: }
SourceFile:kernel/trace/trace_events.c]
|
| 14/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 12669
output: 58
thoughts: 464
Thoughts: **Vulnerability Deep Dive: A Potential Null Pointer Dereference in Ftrace**
Okay, let's break this down. I'm looking at how `__ftrace_set_clr_event_nolock` interacts with the trace cache. It calls `cache_mod`, and I'm focusing on the `set=0` case where it's supposed to *remove* something. Specifically, `remove_cache_mod` is the critical function here.
The core of the issue boils down to how `remove_cache_mod` handles comparisons within the `tr->mod_events` list. It iterates and checks for matching modules, and then, crucially, it checks for matches with the `match` parameter passed in, and `event_mod->match` from the linked list.
The dangerous line is this: `if (match && strcmp(event_mod->match, match) != 0)`. If `match` is *not* NULL, the code attempts to use `strcmp` on `event_mod->match`. Here's the catch: what if `event_mod->match` *is* NULL? That's a classic null pointer dereference vulnerability.
I can see a clear path to triggering this. When `cache_mod` is called with `set=1`, `event_mod` is allocated. If the original call had `match=NULL`, then `event_mod->match` is *also* set to NULL.
So, here's the exploit: Call `__ftrace_set_clr_event_nolock` *first* with `set=1` and `match=NULL` (and some module identifier). This adds an `event_mod` to the list with `match` equal to NULL.
Then, call it *again* with `set=0` and `match` set to *something* that is *not* NULL, but keep the same module identifier. Now, `remove_cache_mod` will iterate the list, find our originally added `event_mod`, and hit that problematic `strcmp(NULL, match)` call, leading to a crash.
I need to trace the call paths to `__ftrace_set_clr_event_nolock` to verify this sequence is possible in a real-world scenario.
|
| 15/2 |
2026/08/09 04:34 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:5 Name:__ftrace_set_clr_event_nolock SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__ftrace_set_clr_event SourceFile:kernel/trace/trace_events.c SourceLine:1410 SourceSnippet:1405:
1406: if (trace_array_is_readonly(tr))
1407: return -EACCES;
1408:
1409: mutex_lock(&event_mutex);
1410: ret = __ftrace_set_clr_event_nolock(tr, match, sub, event, set, mod);
1411: mutex_unlock(&event_mutex);
1412:
1413: return ret;
1414: }
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:event_trace_del_tracer SourceFile:kernel/trace/trace_events.c SourceLine:4672 SourceSnippet:4667:
4668: /* Clear the pid list */
4669: __ftrace_clear_event_pids(tr, TRACE_PIDS | TRACE_NO_PIDS);
4670:
4671: /* Disable any running events */
4672: __ftrace_set_clr_event_nolock(tr, NULL, NULL, NULL, 0, NULL);
4673:
4674: /* Make sure no more events are being executed */
4675: tracepoint_synchronize_unregister();
4676:
4677: down_write(&trace_event_sem);
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:update_mod_cache SourceFile:kernel/trace/trace_events.c SourceLine:3903 SourceSnippet:3898:
3899: list_for_each_entry_safe(event_mod, n, &tr->mod_events, list) {
3900: if (strcmp(event_mod->module, mod->name) != 0)
3901: continue;
3902:
3903: __ftrace_set_clr_event_nolock(tr, event_mod->match,
3904: event_mod->system,
3905: event_mod->event, 1, mod->name);
3906: free_event_mod(event_mod);
3907: }
3908: }
]] TruncatedOutput:false]
|
| 16/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 14362
output: 55
thoughts: 26
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Decoding the `__ftrace_set_clr_event` Call**
Right, so I'm looking at this ftrace function, `__ftrace_set_clr_event`. I see immediately that it's acting as a wrapper, isn't it? It's making a call to `__ftrace_set_clr_event_nolock`. That suggests a pretty standard pattern. The intention is probably to provide a locking mechanism to protect some shared data or resource. `__ftrace_set_clr_event` is the public-facing function and is handling the necessary lock acquisition and release, while `__ftrace_set_clr_event_nolock` is where the actual, more granular work is done. This approach keeps the core logic of setting or clearing the ftrace event isolated from the locking complexity. That's good design β keeps things cleaner and prevents deadlocks. My guess is we'll see a mutex or spinlock being managed in the calling function, depending on the kernel context, but I'd need to trace it to confirm the particular implementation details. Essentially, I'm expecting this to be a classic lock-protected, non-locking helper function paradigm, a common design pattern in kernel code.
|
| 17/2 |
2026/08/09 04:34 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:5 Name:__ftrace_set_clr_event SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:ftrace_set_clr_event SourceFile:kernel/trace/trace_events.c SourceLine:1460 SourceSnippet:1455: /* Allow wildcard for no length or star */
1456: if (!strlen(match) || strcmp(match, "*") == 0)
1457: match = NULL;
1458: }
1459:
1460: ret = __ftrace_set_clr_event(tr, match, sub, event, set, mod);
1461:
1462: /* Put back the colon to allow this to be called again */
1463: if (buf)
1464: *(buf - 1) = ':';
1465:
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:system_enable_write SourceFile:kernel/trace/trace_events.c SourceLine:2034 SourceSnippet:2029: * so the name is safe to use.
2030: */
2031: if (system)
2032: name = system->name;
2033:
2034: ret = __ftrace_set_clr_event(dir->tr, NULL, name, NULL, val, NULL);
2035: if (ret)
2036: goto out;
2037:
2038: ret = cnt;
2039:
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:trace_array_set_clr_event SourceFile:kernel/trace/trace_events.c SourceLine:1514 SourceSnippet:1509:
1510: if (!tr)
1511: return -ENOENT;
1512:
1513: set = (enable == true) ? 1 : 0;
1514: return __ftrace_set_clr_event(tr, NULL, system, event, set, NULL);
1515: }
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:trace_set_clr_event SourceFile:kernel/trace/trace_events.c SourceLine:1488 SourceSnippet:1483: struct trace_array *tr = top_trace_array();
1484:
1485: if (!tr)
1486: return -ENODEV;
1487:
1488: return __ftrace_set_clr_event(tr, NULL, system, event, set, NULL);
1489: }
]] TruncatedOutput:false]
|
| 18/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 15475
output: 41
thoughts: 29
Thoughts: Okay, here's my interpretation of that.
**Analyzing the Function Call Flow in ftrace**
Alright, let's break this down. From looking at this, it seems pretty clear. The function `ftrace_set_clr_event` is getting called *from* `ftrace_event_write`. I can see that relationship, plain as day, from the stack trace. That likely means something is either enabling or disabling an event *before* it gets written to by `ftrace_event_write`. Need to check the parameters in order to determine what it does, likely based on the parameters it receives. This could be a critical point for understanding event filtering, control flow, or even potential race conditions if the enabling/disabling is not handled atomically. I'll need to dig into the implementations of both functions to understand the exact mechanics of that interaction. This is a common pattern in the kernel tracing infrastructure, so I'm not surprised, but knowing the precise relationship is key to debugging trace output and identifying any performance bottlenecks or unexpected behavior.
|
| 19/2 |
2026/08/09 04:34 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:ftrace_set_clr_event]
Results: map[SourceCode:1416: int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
1417: {
1418: char *event = NULL, *sub = NULL, *match, *mod;
1419: int ret;
1420:
1421: if (!tr)
1422: return -ENOENT;
1423:
1424: /* Modules events can be appended with :mod:<module> */
1425: mod = strstr(buf, ":mod:");
1426: if (mod) {
1427: *mod = '\0';
1428: /* move to the module name */
1429: mod += 5;
1430: }
1431:
1432: /*
1433: * The buf format can be <subsystem>:<event-name>
1434: * *:<event-name> means any event by that name.
1435: * :<event-name> is the same.
1436: *
1437: * <subsystem>:* means all events in that subsystem
1438: * <subsystem>: means the same.
1439: *
1440: * <name> (no ':') means all events in a subsystem with
1441: * the name <name> or any event that matches <name>
1442: */
1443:
1444: match = strsep(&buf, ":");
1445: if (buf) {
1446: sub = match;
1447: event = buf;
1448: match = NULL;
1449:
1450: if (!strlen(sub) || strcmp(sub, "*") == 0)
1451: sub = NULL;
1452: if (!strlen(event) || strcmp(event, "*") == 0)
1453: event = NULL;
1454: } else if (mod) {
1455: /* Allow wildcard for no length or star */
1456: if (!strlen(match) || strcmp(match, "*") == 0)
1457: match = NULL;
1458: }
1459:
1460: ret = __ftrace_set_clr_event(tr, match, sub, event, set, mod);
1461:
1462: /* Put back the colon to allow this to be called again */
1463: if (buf)
1464: *(buf - 1) = ':';
1465:
1466: return ret;
1467: }
SourceFile:kernel/trace/trace_events.c]
|
| 20/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 16521
output: 39
thoughts: 224
Thoughts: **My Analysis of the `ftrace_set_clr_event` Parsing and Event Addition**
Okay, let's break down how this works. I see that `ftrace_set_clr_event` starts by parsing the input string. Let's say I write something like `*:mod:foo` to the `set_event` file. I immediately understand what's going on; `mod` becomes "foo" and `buf` is `*`. The `match` becomes `*` and `buf` becomes NULL.
Since there's no system or event given, the code takes the `else if (mod)` path. Because `match` is `*`, it gets assigned NULL. Now, `__ftrace_set_clr_event` gets invoked, but with `match=NULL`, `sub=NULL`, `event=NULL`, `set=1`, and `mod="foo"`.
Effectively, this means it's calling `cache_mod` with the module name "foo". This is the important bit. `cache_mod` then adds an `event_mod` entry to whatever internal data structure it uses. The crucial thing is that this `event_mod` has `module="foo"` and `match` remains NULL.
Now, if I try to write something like `!bar:mod:foo`, there's the initial parsing and then... hmm, I'm pretty sure that the `!` prefix is handled at a higher level, specifically within `ftrace_event_write`. I need to review that function to understand precisely how the negation is interpreted. This is something that would be good to have in a test case!
|
| 21/2 |
2026/08/09 04:34 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:ftrace_event_write]
Results: map[SourceCode:1521: static ssize_t
1522: ftrace_event_write(struct file *file, const char __user *ubuf,
1523: size_t cnt, loff_t *ppos)
1524: {
1525: struct trace_parser parser;
1526: struct seq_file *m = file->private_data;
1527: struct trace_array *tr = m->private;
1528: ssize_t read, ret;
1529:
1530: if (!cnt)
1531: return 0;
1532:
1533: ret = tracing_update_buffers(tr);
1534: if (ret < 0)
1535: return ret;
1536:
1537: if (trace_parser_get_init(&parser, EVENT_BUF_SIZE + 1))
1538: return -ENOMEM;
1539:
1540: read = trace_get_user(&parser, ubuf, cnt, ppos);
1541:
1542: if (read >= 0 && trace_parser_loaded((&parser))) {
1543: int set = 1;
1544:
1545: if (*parser.buffer == '!')
1546: set = 0;
1547:
1548: ret = ftrace_set_clr_event(tr, parser.buffer + !set, set);
1549: if (ret)
1550: goto out_put;
1551: }
1552:
1553: ret = read;
1554:
1555: out_put:
1556: trace_parser_put(&parser);
1557:
1558: return ret;
1559: }
SourceFile:kernel/trace/trace_events.c]
|
| 22/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 17682
output: 52
thoughts: 900
Thoughts: **Analyzing a Kernel NULL Pointer Dereference in Ftrace**
Okay, so I've traced through this ftrace code, and it's pretty clear where the vulnerability lies. The `!` operator in the `set_event` file, which translates to a "set=0" operation, is the key. Let's break it down:
If I write something like `!bar:mod:foo` to `set_event`:
1. `mod` gets set to `foo`, and `buf` to `bar`.
2. `match` is initialized as `bar`, then updated to NULL.
3. The crucial `__ftrace_set_clr_event` function gets called with `mod="foo"`, and `match="bar"`, but `set=0`.
4. This, in turn, calls `remove_cache_mod(tr, "foo", "bar", NULL, NULL)`.
The problem appears in `remove_cache_mod`:
```c
list_for_each_entry_safe(event_mod, n, &tr->mod_events, list) {
if (strcmp(event_mod->module, mod) != 0)
continue;
if (match && strcmp(event_mod->match, match) != 0)
continue;
```
It looks for an `event_mod` where `module` is `"foo"`. `match` is `"bar"` and is not NULL. The code then compares the existing `event_mod->match` with the new `match`. But `event_mod->match` *was* initially set to NULL during the first write (e.g., `*:mod:foo`).
Here's the verification:
* Write 1: `*:mod:foo` sets `mod` to `foo`, `buf` to `*`, `match` becomes `*` and then NULL. `event_mod->match` becomes NULL in the cache.
* Write 2: `!bar:mod:foo` triggers the `remove_cache_mod` function. This causes the code to execute `strcmp(event_mod->match, match)` i.e. `strcmp(NULL, "bar")`, which results in a NULL pointer dereference.
The KASAN output confirms that it's a read from the NULL address. The address accessed `dfff800000000000` is the KASAN shadow address for NULL. This is a classic kernel oops. If I had KASAN not enabled, it would have just dereferenced NULL.
While this isn't exploitable for privilege escalation or memory corruption because it's just a read of NULL, it's a Denial of Service (DoS). It can crash the kernel (if `panic_on_oops` is set) or at least kill the process. This specific crash can leave the `event_mutex` held, causing deadlock, effectively DoSing any other process using ftrace. It appears that `event_mutex` is held during `__ftrace_set_clr_event_nolock`. If the process crashes while holding that lock, any subsequent ftrace access will hang.
Now, the important question is: can an unprivileged process trigger this? This bug is triggered by writing to the `set_event` file in tracefs, which is typically mounted at `/sys/kernel/tracing` or `/sys/kernel/debug/tracing`. Now I need to check the permissions of `set_event` and see if an unprivileged user can exploit it.
|
| 23/2 |
2026/08/09 04:34 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:5 Name:ftrace_event_write SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:ftrace_set_event_fops SourceFile:kernel/trace/trace_events.c SourceLine:2648 SourceSnippet:2645: static const struct file_operations ftrace_set_event_fops = {
2646: .open = ftrace_event_set_open,
2647: .read = seq_read,
2648: .write = ftrace_event_write,
2649: .llseek = seq_lseek,
2650: .release = ftrace_event_release,
2651: };
]] TruncatedOutput:false]
|
| 24/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 19613
output: 55
thoughts: 19
Thoughts: Here's my take on those thoughts:
**Tracing the Use of ftrace_set_event_fops**
Okay, so I'm digging into `ftrace_set_event_fops`. Time to trace its usage. I need to understand where this function is actually called within the system. My initial instinct is to use cross-referencing tools or a debugger to find all the instances where `ftrace_set_event_fops` is invoked. This will give me a better understanding of how the function fits into the overall event tracing framework and how it's being utilized in the kernel's tracing mechanism. Essentially, I need to see the contexts where the function is setting up file operations for the trace events. This will illuminate what parts of the code are directly interacting with this function.
|
| 25/2 |
2026/08/09 04:34 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:5 Name:ftrace_set_event_fops SourceTreePrefix:]
Results: map[References:<nil> TruncatedOutput:false]
|
| 26/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 19873
output: 29
thoughts: 28
Thoughts: Okay, here's my attempt at summarizing those thoughts from a first-person, expert perspective:
**Finding the `set_event` Function**
Right, so I see it's used in `kernel/trace/trace_events.c`. That's not entirely surprising, given the context. My initial instinct is to dig deeper and see how `set_event` is actually used within that file and the broader tracing framework. My next step will be to search within that same file for the function `set_event`. That seems like the most logical starting point for understanding its role and interactions.
|
| 27/2 |
2026/08/09 04:34 |
tool |
grepper |
0m
Args: map[Expression:"set_event" PathPrefix:kernel/trace/]
Results: map[Output:kernel/trace/trace_events.c=4545=create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
--
kernel/trace/trace_events.c-4567- if (!trace_array_is_readonly(tr)) {
kernel/trace/trace_events.c:4568: entry = trace_create_file("set_event", TRACE_MODE_WRITE, parent,
kernel/trace/trace_events.c-4569- tr, &ftrace_set_event_fops);
]
|
| 28/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 20206
output: 31
thoughts: 20
Thoughts: Here's my summary, as the expert:
**Checking TRACE_MODE_WRITE Permissions**
Okay, so I'm thinking about `TRACE_MODE_WRITE`. Typically, I expect it to be set with `0644` permissions. That's the common practice for a file like this, readable by the owner and group, and read-only for others. Let's just double-check that this is indeed the case. No point assuming, even with common conventions. It's always best to verify, especially when dealing with potentially sensitive data.
|
| 29/2 |
2026/08/09 04:34 |
tool |
grepper |
0m
Args: map[Expression:define TRACE_MODE_WRITE PathPrefix:kernel/trace/]
Results: map[Output:kernel/trace/trace.h-33-
kernel/trace/trace.h:34:#define TRACE_MODE_WRITE 0640
kernel/trace/trace.h-35-#define TRACE_MODE_READ 0440
]
|
| 30/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 20449
output: 32
thoughts: 79
Thoughts: **Investigating Tracefs Mountability in User Namespaces**
Okay, so looking at the permissions, `0640` translates to read/write for the owner, read-only for the group, and no access for others. Typically, the owner in this context would be root, which is important to consider. My primary question now centers around `tracefs` and its ability to be mounted within a user namespace. If I can mount `tracefs` inside a user namespace, that would open up the possibility of unprivileged users having access to it within that isolated environment. This is a critical point; if it's mountable, it means I can potentially achieve something valuable for that user. Therefore, I need to confirm whether `tracefs` *can* actually be mounted in a user namespace. That's the core question I'm trying to answer here.
|
| 31/2 |
2026/08/09 04:34 |
tool |
grepper |
0m
Error:
Args: map[Expression:FS_USERNS_MOUNT PathPrefix:fs/tracefs/]
Results:
|
| 32/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 20755
output: 30
thoughts: 14
Thoughts: Here's my take on the thought process, summarized as you requested:
**Diving into `fs/tracefs/inode.c`**
Okay, time to dig in. Let's start by taking a look at `fs/tracefs/inode.c`. I'm curious to see how the tracefs inodes are handled, specifically the inode operations and how they interact with the trace infrastructure. I want to understand the lifecycle of these inodes, how they're created, and how they contribute to the overall tracing mechanism within the kernel. It's likely that a thorough understanding here is key to understanding and potentially debugging any issues in tracefs. I need to refresh my understanding of how this module interfaces with the overall VFS layer.
|
| 33/2 |
2026/08/09 04:34 |
tool |
grepper |
0m
Args: map[Expression:trace_fs_type PathPrefix:fs/tracefs/]
Results: map[Output:fs/tracefs/inode.c=502=static int tracefs_init_fs_context(struct fs_context *fc)
--
fs/tracefs/inode.c-516-
fs/tracefs/inode.c:517:static struct file_system_type trace_fs_type = {
fs/tracefs/inode.c-518- .owner = THIS_MODULE,
--
fs/tracefs/inode.c=526=struct dentry *tracefs_start_creating(const char *name, struct dentry *parent)
--
fs/tracefs/inode.c-532-
fs/tracefs/inode.c:533: error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
fs/tracefs/inode.c-534- &tracefs_mount_count);
--
fs/tracefs/inode.c=758=void tracefs_remove(struct dentry *dentry)
--
fs/tracefs/inode.c-762-
fs/tracefs/inode.c:763: simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count);
fs/tracefs/inode.c-764- simple_recursive_removal(dentry, remove_one);
--
fs/tracefs/inode.c=787=static int __init tracefs_init(void)
--
fs/tracefs/inode.c-802-
fs/tracefs/inode.c:803: retval = register_filesystem(&trace_fs_type);
fs/tracefs/inode.c-804- if (!retval)
]
|
| 34/2 |
2026/08/09 04:34 |
llm |
expert |
0m
Model:
Tokens:
input: 21381
output: 37
thoughts: 13
Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're my own:
**Analyzing the `trace_fs_type` Definition**
Alright, time to get my hands dirty. It looks like I need to really understand how `trace_fs_type` is defined. I'm going to pull up the definition. I need to see what's under the hood, all the structural elements. This is core infrastructure, so I need to know precisely how it's put together. What are the key data structures involved? What are the implications of the design choices? Let's get to the nitty-gritty and see what this thing *really* does. Understanding this definition is going to be key to whatever I'm troubleshooting or building.
|
| 35/2 |
2026/08/09 04:35 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/tracefs/inode.c Name:trace_fs_type]
Results: map[SourceCode: 517: static struct file_system_type trace_fs_type = {
518: .owner = THIS_MODULE,
519: .name = "tracefs",
520: .init_fs_context = tracefs_init_fs_context,
521: .parameters = tracefs_param_specs,
522: .kill_sb = kill_anon_super,
523: };
SourceFile:fs/tracefs/inode.c]
|
| 36/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 21749
output: 38
thoughts: 812
Thoughts: **Tracefs Security Analysis**
Okay, so I'm looking at this `tracefs` situation, and my initial thought is that it's not mountable in a user namespace by an unprivileged user because it lacks the `FS_USERNS_MOUNT` capability. But, hold on, what about `tracefs` delegation? I know there *is* delegation to non-root users, but that's an administrative action, not something available by default. By default, `tracefs` is locked down to root access only. Therefore, unprivileged processes simply cannot access it.
Even if we *could* create a user namespace, it wouldn't help. We still can't mount it there. But just to be sure, even if root in the initial namespace mounts it, a user *inside* a user namespace would be blocked because the tracefs files are owned by root in the initial namespace, which maps to `nobody` in the user namespace, and the file permissions (0640) don't give `nobody` read/write access.
What about a process that has `CAP_SYS_ADMIN` inside a user namespace? Nope, we're still stuck because the critical `FS_USERNS_MOUNT` flag is missing, preventing the mount altogether.
So, let's look for other ways to get access, specifically, other ways to write to `set_event`. Is there an `ioctl` or something sneaky? Nope, just plain file writes.
Now, let's try to break this down by finding how to trigger this bug, focusing on the call to `remove_cache_mod`, that's called from `cache_mod`, which is called from `__ftrace_set_clr_event_nolock`.
`__ftrace_set_clr_event_nolock` is called from three different places:
- `__ftrace_set_clr_event`
- `event_trace_del_tracer`
- `update_mod_cache`
`event_trace_del_tracer` calls it with `match=NULL`, `sub=NULL`, `event=NULL`, `set=0`, `mod=NULL`. That won't trigger the bug, because `mod` is NULL, and so, the `cache_mod` function is not called.
`update_mod_cache` is called when a module is loaded, and it passes in `match=event_mod->match`, `sub=event_mod->system`, `event=event_mod->event`, `set=1`, `mod=mod->name`. It iterates through a list of `event_mod` structures.
```c
list_for_each_entry_safe(event_mod, n, &tr->mod_events, list) {
if (strcmp(event_mod->module, mod->name) != 0)
continue;
__ftrace_set_clr_event_nolock(tr, event_mod->match,
event_mod->system,
event_mod->event, 1, mod->name);
free_event_mod(event_mod);
}
```
If `event_mod->match` is NULL in that loop, it calls `__ftrace_set_clr_event_nolock` with `match=NULL`. That's fine, because it won't trigger the bug either.
So, the only way to trigger this bug is to call `__ftrace_set_clr_event_nolock` with `set=0` and `match!=NULL` and `mod!=NULL`, when there is an `event_mod` with `match=NULL` and the same `mod`.
This can only be done by writing to `set_event`. `set_event_pid` doesn't use this function.
Wait a second, there's `system_enable_write` that calls `__ftrace_set_clr_event`. I'll have to look at that closer.
|
| 37/2 |
2026/08/09 04:35 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:system_enable_write]
Results: map[SourceCode:2006: static ssize_t
2007: system_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
2008: loff_t *ppos)
2009: {
2010: struct trace_subsystem_dir *dir = filp->private_data;
2011: struct event_subsystem *system = dir->subsystem;
2012: const char *name = NULL;
2013: unsigned long val;
2014: ssize_t ret;
2015:
2016: ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
2017: if (ret)
2018: return ret;
2019:
2020: ret = tracing_update_buffers(dir->tr);
2021: if (ret < 0)
2022: return ret;
2023:
2024: if (val != 0 && val != 1)
2025: return -EINVAL;
2026:
2027: /*
2028: * Opening of "enable" adds a ref count to system,
2029: * so the name is safe to use.
2030: */
2031: if (system)
2032: name = system->name;
2033:
2034: ret = __ftrace_set_clr_event(dir->tr, NULL, name, NULL, val, NULL);
2035: if (ret)
2036: goto out;
2037:
2038: ret = cnt;
2039:
2040: out:
2041: *ppos += cnt;
2042:
2043: return ret;
2044: }
SourceFile:kernel/trace/trace_events.c]
|
| 38/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 24013
output: 42
thoughts: 49
Thoughts: Okay, here's my interpretation of those thoughts, presented as my own mental process, with the bolded header as requested:
**Diving into the Ftrace Event Setting Logic**
Alright, let's see, the initial thought process seems to be focused on a specific function call, `system_enable_write`. Hmm, that function's behavior with respect to triggering a potential issue is the first thing that needs understanding. It is calling `__ftrace_set_clr_event`. Ok, the key observation here is that the function is being called with `mod=NULL`. Good, this probably rules out the scenario where the suspected bug comes into play, given what I know about the typical conditions required for this type of ftrace problem. It's likely the check against `mod` is an important part of the problem.
But, hold on...that's just one path. What about `trace_array_set_clr_event`? We need to also consider what happens when that function is called. The fact that this function is now on my mind suggests this might be the location of the bug. It's time to dig deeper into the call stack to see if that function is handling the parameters in a way that creates an issue. I'll need to check the logic there, perhaps there is a nuance with event setting that makes the bug show up when called from this function.
|
| 39/2 |
2026/08/09 04:35 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:trace_array_set_clr_event]
Results: map[SourceCode:1492: /**
1493: * trace_array_set_clr_event - enable or disable an event for a trace array.
1494: * @tr: concerned trace array.
1495: * @system: system name to match (NULL for any system)
1496: * @event: event name to match (NULL for all events, within system)
1497: * @enable: true to enable, false to disable
1498: *
1499: * This is a way for other parts of the kernel to enable or disable
1500: * event recording.
1501: *
1502: * Returns 0 on success, -EINVAL if the parameters do not match any
1503: * registered events.
1504: */
1505: int trace_array_set_clr_event(struct trace_array *tr, const char *system,
1506: const char *event, bool enable)
1507: {
1508: int set;
1509:
1510: if (!tr)
1511: return -ENOENT;
1512:
1513: set = (enable == true) ? 1 : 0;
1514: return __ftrace_set_clr_event(tr, NULL, system, event, set, NULL);
1515: }
SourceFile:kernel/trace/trace_events.c]
|
| 40/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 24793
output: 40
thoughts: 22
Thoughts: Okay, here's my interpretation of those thoughts, framed as an expert's inner monologue:
**Investigating a Null Module Call and Event Clearing**
Alright, so the code's making a call with `mod=NULL`. That's an interesting quirk. I need to figure out what's happening there and what the implications are. Typically, a NULL module pointer is...well, problematic if it's not handled gracefully. It could be an early initialization state, a deliberate clearing, or a sign of a deeper bug. I need to trace this back and see how that variable gets populated, and why it's potentially getting cleared. What context surrounds that call? Are there any obvious error checks around it?
Then there's `trace_set_clr_event`. The presence of this function piqued my interest. What is this clearing event? Is it a way to clear flags, or a logging component? I need to understand its purpose and relationship to that `mod=NULL` call. Are they related? Does the clearing event somehow interact with or rely on that null module pointer? A clearing event might be used to reset some system component, such as a buffer used for tracing data, so this call could be essential to maintain a clear record of the system as it operates. I need to delve into the implementation of this function and see how it interacts with the broader tracing framework. The goal now is to establish if `trace_set_clr_event` and the `mod=NULL` call are connected and, if so, in what manner.
|
| 41/2 |
2026/08/09 04:35 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:trace_set_clr_event]
Results: map[SourceCode:1469: /**
1470: * trace_set_clr_event - enable or disable an event
1471: * @system: system name to match (NULL for any system)
1472: * @event: event name to match (NULL for all events, within system)
1473: * @set: 1 to enable, 0 to disable
1474: *
1475: * This is a way for other parts of the kernel to enable or disable
1476: * event recording.
1477: *
1478: * Returns 0 on success, -EINVAL if the parameters do not match any
1479: * registered events.
1480: */
1481: int trace_set_clr_event(const char *system, const char *event, int set)
1482: {
1483: struct trace_array *tr = top_trace_array();
1484:
1485: if (!tr)
1486: return -ENODEV;
1487:
1488: return __ftrace_set_clr_event(tr, NULL, system, event, set, NULL);
1489: }
SourceFile:kernel/trace/trace_events.c]
|
| 42/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 25530
output: 54
thoughts: 104
Thoughts: **Analyzing the Vulnerability's Reachability**
Okay, so I'm looking at this and the key is `mod=NULL`. That's the critical piece. This means the only entry point to trigger the bug is through `ftrace_set_clr_event`. Now, where does *that* get called? Right, it's called by `ftrace_event_write` specifically when we're writing to the `set_event` file within tracefs.
So, the vulnerability is, in effect, confined to interactions with the `set_event` file within the tracefs filesystem. That's good from a security perspective... but let's not get ahead of ourselves. As we know, tracefs, by default, is only accessible to root within the initial user namespace. That sounds restrictive, but we need to be absolutely certain. Let's double-check. Just to be thorough, I'm going to scan the code again to verify there aren't any other call sites for `ftrace_set_clr_event` that we might be overlooking. We can't afford any gaps in this analysis.
|
| 43/2 |
2026/08/09 04:35 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:5 Name:ftrace_set_clr_event SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__early_set_events SourceFile:kernel/trace/trace_events.c SourceLine:4705 SourceSnippet:4700: char *token;
4701:
4702: while ((token = strsep(&buf, ","))) {
4703: if (*token) {
4704: if (enable) {
4705: if (ftrace_set_clr_event(tr, token, 1))
4706: pr_warn("Failed to enable trace event: %s\n", token);
4707: } else {
4708: ftrace_set_clr_event(tr, token, 0);
4709: }
4710: }
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__early_set_events SourceFile:kernel/trace/trace_events.c SourceLine:4708 SourceSnippet:4703: if (*token) {
4704: if (enable) {
4705: if (ftrace_set_clr_event(tr, token, 1))
4706: pr_warn("Failed to enable trace event: %s\n", token);
4707: } else {
4708: ftrace_set_clr_event(tr, token, 0);
4709: }
4710: }
4711:
4712: /* Put back the comma to allow this to be called again */
4713: if (buf)
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:ftrace_event_write SourceFile:kernel/trace/trace_events.c SourceLine:1548 SourceSnippet:1543: int set = 1;
1544:
1545: if (*parser.buffer == '!')
1546: set = 0;
1547:
1548: ret = ftrace_set_clr_event(tr, parser.buffer + !set, set);
1549: if (ret)
1550: goto out_put;
1551: }
1552:
1553: ret = read;
]] TruncatedOutput:false]
|
| 44/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 26576
output: 32
thoughts: 657
Thoughts: **My Assessment of the Tracefs NULL Pointer Dereference**
Okay, so I've been digging into this potential security issue, and here's my take. The core of the problem lies in the `__early_set_events` function. It's triggered when parsing the kernel command line, specifically when using the `trace_event=` parameter. `setup_trace_events` is the gateway. This means I can potentially trigger it with something like `trace_event=*:mod:foo,!bar:mod:foo` during boot, but, realistically, that's a root-level privilege, or bootloader level, so it's not a general attack vector.
The vulnerability itself is a NULL pointer dereference. The `dfff800000000000` address is being accessed which looks like KASAN shadow for NULL. Without KASAN, itβs a read from NULL. This causes a kernel oops, which is annoying, but doesn't lead to memory corruption, privilege escalation, or any kind of information leakage. I'm not seeing any immediate way to leverage this into something worse.
So, the impact seems limited to Denial of Service (DoS). The oops can panic the kernel if `panic_on_oops` is set, which is definitely a bad day. Even if not, it kills the process holding the `event_mutex`, effectively deadlocking the ftrace system. That's a reliable DoS condition.
I've checked for other triggers. No guest VM vulnerabilities, nothing in confidential computing, no network or peripheral triggers. It's localized to the host kernel's ftrace implementation. It doesn't look like any other interface exposes `ftrace_event_write` directly; it's locked down to the `set_event` file in tracefs.
To summarize, this NULL pointer dereference is happening in `strcmp` called from `remove_cache_mod`. It happens when `event_mod->match` becomes NULL if `cache_mod` was called with `match=NULL`. This happens when you write `*:mod:<module>` to `set_event`. Later, writing `!bar:mod:<module>` triggers `remove_cache_mod` with `match="bar"`. That then dereferences the NULL `event_mod->match`.
It is a read-only NULL pointer, and thus, not exploitable for privilege escalation or information leakage. It *is* a DoS, via a kernel oops and potential deadlock. The real kicker is that tracefs is only accessible to root (0640 permissions, owned by root), and user namespaces are a no-go for mounting tracefs.
Now, I'll need to double-check if there's some obscure kernel configuration or newer version that accidentally allows `tracefs` to be mounted in a user namespace, but as it stands, this is a pretty contained, root-level DoS vulnerability.
|
| 45/2 |
2026/08/09 04:35 |
tool |
grepper |
0m
Error:
Args: map[Expression:FS_USERNS_MOUNT PathPrefix:fs/tracefs/]
Results:
|
| 46/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 27904
output: 32
thoughts: 54
Thoughts: Okay, here's my take on those thoughts, framed as my own reasoning:
**Checking Debugfs for Trace Event Access**
Hold on a second, that doesn't sound quite right. Let's dig deeper and see if we can get access to the `set_event` functionality through `debugfs`. I know that `tracefs` is typically mounted within `/sys/kernel/debug/tracing`, and I want to verify if the event settings are accessible there. I also need to keep in mind that `debugfs` can't be mounted inside a user namespace. That restriction will influence my approach.
|
| 47/2 |
2026/08/09 04:35 |
tool |
grepper |
0m
Error:
Args: map[Expression:FS_USERNS_MOUNT PathPrefix:fs/debugfs/]
Results:
|
| 48/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 28133
output: 66
thoughts: 499
Thoughts: **My Assessment of the `set_event` Vulnerability**
Okay, let's break this down. First, this isn't something that can be exploited directly from a user namespace. That's a non-starter.
My next line of inquiry is how we *could* potentially write to `set_event`. I'm thinking about `tracefs` delegation. Could that be a vector? Well, there's a delegation feature, but that requires explicit administrator action to grant access to a group. We're assuming the default config, so that's not it either.
Alright, the focus is now on finding alternative paths where `cache_mod` could be called with a `match=NULL` value. It looks like `__ftrace_set_clr_event_nolock` is the key. Specifically, when `module` is set, `ret` is `-EINVAL`, and `!eret`, then `cache_mod` gets called. This seems to happen when an event isn't found for a given module.
Now, let's explore this edge case. If I try to write something like `"foo:mod:bar"` where `"foo"` doesn't exist, `match` will become `"foo"`, and so `event_mod->match` gets that value. If I write something like `"*:mod:bar"`, `match` is `NULL`, which sets `event_mod->match` to null. Same thing with `"sys:foo:mod:bar"`, `match` is null, which leaves `event_mod->match` as null. But what if I write `"!baz:mod:bar"`? Now the game changes!
`remove_cache_mod` is going to do a `strcmp` comparison of `event_mod->match` (which is `NULL`) to `"baz"`...and that's a recipe for a crash.
So, this is a very straightforward reproduction: root can easily trigger it.
Alright, the final assessment:
* **Exploitable:** No. It's a NULL pointer dereference on read.
* **Denial of Service:** Yes. Kernel oops and possible deadlocks.
* **Unprivileged:** No. Requires root access.
* **UserNamespace:** No.
* **VMGuestTrigger:** No.
* **VMHostTrigger:** No.
* **NetworkTrigger:** No.
* **RemoteTrigger:** No.
* **PeripheralTrigger:** No.
* **FilesystemTrigger:** No.
|
| 49/2 |
2026/08/09 04:35 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 50/2 |
2026/08/09 04:35 |
llm |
expert |
0m
Model:
Tokens:
input: 29307
output: 525
thoughts: 326
Thoughts: **Final Thoughts on the Kernel Trace Event Bug**
Okay, the analysis is complete, and it's time to put together the final assessment. Here's what I've got:
Essentially, this boils down to a NULL pointer dereference. The culprit is the `strcmp` function, triggered within `remove_cache_mod` which is found in `kernel/trace/trace_events.c`. The problem surfaces when a user, likely root, crafts a wildcard module event filter, something like `*:mod:foo`, and writes it to the `set_event` file within tracefs. That sets up a situation where the cached module event ends up with a NULL `match` string. Then, a subsequent attempt to remove a specific event filter, something like `!bar:mod:foo`, fires off a `remove_cache_mod` call. Inside that, the code tries to compare the new, specific filter's match string with the cached NULL `match` using `strcmp`. That's where the NULL pointer dereference happens.
Now, while it's a read from a NULL pointer, so not a textbook exploitable vulnerability for memory corruption, privilege escalation, or any information leak, it's still significant. This is a kernel oops waiting to happen, immediately killing the offending process while it holds the `event_mutex`. That means any further ftrace operations are going to deadlock, essentially leading to a Denial of Service. Not ideal, to say the least.
The good news, if you can call it that, is the limited scope. The `set_event` file lives in tracefs, usually mounted at either `/sys/kernel/tracing` or `/sys/kernel/debug/tracing`. This means that by default, the file permissions are `0640` and owned by root. Unprivileged users are locked out from accessing them. On top of that, tracefs doesn't have the `FS_USERNS_MOUNT` flag set, preventing it from being mounted inside a user namespace. This confines the bug's reach to the root user in the initial namespace, although it remains a potentially dangerous condition for that privileged user.
|
| 51/1 |
2026/08/09 04:35 |
action |
format-explanation |
0m
Results: map[Explanation:**Bug Analysis:**
The bug is a NULL pointer dereference in `strcmp()` called from
`remove_cache_mod()` in `kernel/trace/trace_events.c`.
It is triggered via the ftrace `set_event` interface. When a user writes a
wildcard module event filter (e.g., `*:mod:foo`) to the `set_event` file, the
kernel caches this filter using `cache_mod()`. Because of the wildcard `*`, the
`match` string is passed as `NULL`, resulting in an `event_mod` entry where
`event_mod->match` is `NULL`.
Subsequently, if the user writes a specific event filter to remove it (e.g.,
`!bar:mod:foo`), `remove_cache_mod()` is invoked. This function iterates over
the cached module events and attempts to compare the new match string (`"bar"`)
with the cached one using `strcmp(event_mod->match, match)`. Since
`event_mod->match` is `NULL`, this results in a NULL pointer dereference.
**Security Impact:**
* **Exploitable:** No. The bug is a simple read from a NULL pointer (or its
KASAN shadow equivalent). It does not provide any primitives for memory
corruption, arbitrary execution, or information leaks.
* **Denial Of Service:** Yes. Triggering the bug causes a kernel oops. Even if
`panic_on_oops` is not set, the process will be killed while holding the global
`event_mutex`. This leaves the mutex permanently locked, deadlocking any future
attempts to use or configure ftrace on the system.
* **Accessible From Unprivileged Processes:** No. The bug is triggered by
writing to the `set_event` file in `tracefs` (usually mounted at
`/sys/kernel/tracing` or `/sys/kernel/debug/tracing`). By default, these files
have `0640` permissions and are owned by root, meaning unprivileged users cannot
access them.
* **Accessible From User Namespaces:** No. The `tracefs` and `debugfs`
filesystems do not have the `FS_USERNS_MOUNT` flag set. Therefore, they cannot
be mounted by an unprivileged user inside a user namespace.
* **Other Triggers:** The bug is strictly tied to the ftrace configuration
interface and cannot be triggered via network traffic, malicious filesystems,
peripherals, or VM guest interactions.]
|