FAILED: patch "[PATCH] tracing: Fix NULL dereference when copying keys for a field" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x a0777b9e53157f1f6848a0fd0650f5465391ea81
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026102127-agreeable-wisplike-bc63@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a0777b9e53157f1f6848a0fd0650f5465391ea81 Mon Sep 17 00:00:00 2001
From: Donggeun Yoo <[email protected]>
Date: Mon, 14 Sep 2026 14:34:43 +0900
Subject: [PATCH] tracing: Fix NULL dereference when copying keys for a field
variable

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.

index 8af97fd4ee2d..b3df8862855f 100644
@@ -3090,7 +3090,7 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 		key_field = hist_data->fields[i];
 		if (!first)
 			seq_buf_putc(&s, ',');
-		seq_buf_puts(&s, key_field->field->name);
+		expr_field_str(key_field, &s);
 		first = false;
 	}
 

From: Donggeun Yoo <[email protected]>

[ Upstream commit a0777b9e53157f1f6848a0fd0650f5465391ea81 ]

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.

---
 kernel/trace/trace_events_hist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 5659009450caf..187b59350ee1f 100644
@@ -2527,7 +2527,7 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 		key_field = hist_data->fields[i];
 		if (!first)
 			strcat(cmd, ",");
-		strcat(cmd, key_field->field->name);
+		expr_field_str(key_field, cmd);
 		first = false;
 	}
 

2.53.0