CVE-2026-99140

In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix hist trigger timestamps for buffered events

Syzkaller triggered a WARN_ON_ONCE(!nest) warning:

WARNING: kernel/trace/ring_buffer.c:821 at ring_buffer_event_time_stamp Call trace: ring_buffer_event_time_stamp hist_field_timestamp hist_fn_call event_hist_trigger event_triggers_call __event_trigger_test_discard trace_event_buffer_commit do_trace_event_raw_event_sched_switch trace_event_raw_event_sched_switch

The warning is probabilistically reproducible and is related to syzkaller executing the following commands:

echo prev_pid == 999999 > events/sched/sched_switch/filter echo hist:keys=common_timestamp > events/sched/sched_switch/trigger

The specific triggering process is as follows:

CPU 0 CPU 1 (context switching) (echo hist:keys=common_timestamp > events/sched/sched_switch/trigger) do_trace_event_raw_event_##call trace_event_buffer_lock_reserve if (!tr->no_filter_buffering_ref && trace_file->flags & EVENT_FILE_FL_FILTERED) return entry; // return directly event_hist_trigger_parse hist_register_trigger tracing_set_filter_buffering(file->tr, true); tr->no_filter_buffering_ref++; __trace_buffer_lock_reserve rb_start_commit local_inc(&cpu_buffer->committing); // skipped and not executed trace_event_buffer_commit __event_trigger_test_discard event_triggers_call event_hist_trigger hist_fn_call hist_field_timestamp ring_buffer_event_time_stamp nest = local_read(&cpu_buffer->committing); WARN_ON_ONCE(!nest) // trigger warning

The root cause is that when an event file has a filter attached and the hist trigger has not yet been attached, trace_event_buffer_lock_reserve() writes the event into the per-CPU trace_buffered_event temp buffer instead of reserving it in the ring buffer, so cpu_buffer->committing is not incremented. When the event is later processed at commit time by a hist trigger, hist_field_timestamp() -> ring_buffer_event_time_stamp() sees a zero committing count, triggering WARN_ON_ONCE(!nest).

tracing_event_time_stamp() was added by commit d8279bfc5e959 (tracing: Add tracing_event_time_stamp() API) for exactly this case: if the event is the per-CPU trace_buffered_event, it returns the current ring buffer timestamp. But it never gained a caller. Use it in hist_field_timestamp(), so that a hist trigger that races onto a buffered event records the current time, which is only marginally later than when the event was recorded, instead of warning and recording a bogus timestamp.

Affected Software

References

• https://git.kernel.org/stable/c/09c7cce2e59e6b3b1807520bcb1980c561f15d1e
• https://git.kernel.org/stable/c/71c5c7420478d94d6eb0b427f66fa41bbda651e3
• https://git.kernel.org/stable/c/89e90b16aadd6e66bd0323bc8dfc76a62e756b57
• https://git.kernel.org/stable/c/9414ca3b99e5a7f1f3bf51c2a01b383e1b355dd0
• https://git.kernel.org/stable/c/ab320f6aa3769480f735ed0ad026c4a61799b7bc
• https://git.kernel.org/stable/c/af192a356e9830a0df231b590ad6fb1fc28c9315
• https://git.kernel.org/stable/c/b3a94a79047d3fc9385b3709cb2b86f4a26ed0c3