tracing: Fix NULL dereference when copying keys for a field variable

Browse source

In event_hist_trigger_parse() where it needs to create actions like
"onmatch", it calls:

  event_hist_trigger_parse() {
    create_actions() {
      action_create() {
        trace_action_create() {
          trace_action_create_field_var() {
            create_field_var_hist()

Where create_field_var_hist() does a loop on the hist_data
representing the keys. The issue is, if the keys uses one of the
pseudo field types (like common_cpu), the hist_data field element
will have NULL for its field member causing a NULL pointer
dereference when accessing the key_field->field->name.

  # echo 'hist:keys=common_cpu:ts0=common_timestamp.usecs' > \
      events/sched/sched_waking/trigger
  # echo 'my_synth u64 lat; int prio' > synthetic_events
  # echo 'hist:keys=common_cpu:wakeup_lat=common_timestamp.usecs-$ts0:\
      onmatch(sched.sched_waking).my_synth($wakeup_lat,prio)' > \
      events/sched/sched_switch/trigger

  KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
  RIP: 0010:create_field_var_hist+0x771/0x1380
  Call Trace:
   trace_action_create_field_var+0x360/0x600
   trace_action_create+0x393/0xe80
   event_hist_trigger_parse+0x3e47/0x69e0
   trigger_process_regex+0x1a6/0x250
   event_trigger_write+0xce/0x160

Instead of accessing it directly, use the proper handler
expr_field_str() to get the name.

The three previous patches are prerequisites: without them a .buckets
key and a common_stacktrace key each render into a command that cannot
be parsed back.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260914053443.981201-5-donggeunyoo.kernel@gmail.com
Fixes: 02205a6752 ("tracing: Add support for 'field variables'")
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Assisted-by: Claude:claude-fable-5
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

...

This commit is contained in:

Donggeun Yoo 2026-09-14 14:34:43 +09:00 • committed by Steven Rostedt

parent 24a19b953e

commit a0777b9e53

1 changed files with 1 additions and 1 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

2

kernel/trace/trace_events_hist.c

View file