diff options
| author | Hui Su <sh_def@163.com> | 2026-08-12 01:39:03 +0800 |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2026-08-13 15:38:03 -0400 |
| commit | b69859204d4db3acd86c1c2dadcef0d77b451933 (patch) | |
| tree | a294a374e9ba1049a80edca141ef841fe31cc53e /kernel | |
| parent | db2ddb87143519e20a95aa36c60b36107b736a58 (diff) | |
tracing: Fix NULL pointer dereference in module event cache removal
A module-only event filter such as ":mod:foo" is cached with a NULL
event_mod->match when foo has not been loaded. If a later write tries to
remove a specific match from the same module, remove_cache_mod() passes
the NULL cached match to strcmp(), causing a NULL pointer dereference.
The issue can be reproduced from userspace:
echo ':mod:trace_events_kunit_missing' > /sys/kernel/tracing/set_event
echo '!foo_bar:mod:trace_events_kunit_missing' >> /sys/kernel/tracing/set_event
The second write must be a concatenation (">>") to not include O_TRUNC as
that would cause ftrace_clear_events() to clear the cached modules lines.
The crash was reproduced on x86_64 QEMU while KUnit workers contended on
the event tracing path:
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
RIP: 0010:strcmp+0x10/0x30
Call Trace:
__ftrace_set_clr_event_nolock+0x373/0x4a0
ftrace_set_clr_event+0xf0/0x180
ftrace_event_write+0xdf/0x110
vfs_write+0xf6/0x440
ksys_write+0x68/0xe0
do_syscall_64+0xf9/0x540
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Check event_mod->match before comparing it, consistent with the existing
NULL checks for the cached system and event fields. The mismatched removal
continues to return -EINVAL; a broad cached module filter is removed with
"!:mod:<module>".
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260811173902.1927376-2-sh_def@163.com
Fixes: b355247df104 ("tracing: Cache \":mod:\" events for modules not loaded yet")
Reported-by: syzbot+4d3143c8e28f6266c636@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/6a7a6b7f.9c11d2ce.289b96.00f8.GAE@google.com/
Signed-off-by: Hui Su <sh_def@163.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/trace_events.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index c01b10b99f67..032f741ba616 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -945,7 +945,7 @@ static int remove_cache_mod(struct trace_array *tr, const char *mod, if (strcmp(event_mod->module, mod) != 0) continue; - if (match && strcmp(event_mod->match, match) != 0) + if (match && (!event_mod->match || strcmp(event_mod->match, match) != 0)) continue; if (system && |