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tracing: Set the trace clock before registering the histogram trigger

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hist_register_trigger() puts the trigger on the global named_triggers
list in cmd_ops->init(), and only then sets the trace clock:

	if (data->cmd_ops->init) {
		ret = data->cmd_ops->init(data);
		if (ret < 0)
			goto out;
	}

	if (hist_data->enable_timestamps) {
		ret = tracing_set_clock(file->tr, hist_data->attrs->clock);
		if (ret) {
			hist_err(tr, HIST_ERR_SET_CLOCK_FAIL, errpos(clock));
			goto out;
		}

The clock string is not checked anywhere before that call, so a named
trigger using common_timestamp with an unknown clock fails after it has
already become findable. event_hist_trigger_parse() then frees it
without taking it off the list, and the next lookup by name reads the
freed object:

 ~# cd /sys/kernel/tracing/events/sched/sched_switch
 ~# echo 'hist:name=foo:keys=common_pid:ts=common_timestamp:clock=bogus' > trigger
 bash: echo: write error: Invalid argument
 ~# echo 'hist:name=foo:keys=common_pid' > trigger

  BUG: KASAN: slab-use-after-free in find_named_trigger+0xac/0xc0
  Read of size 8 at addr ffff88800915d760 by task init/1
   find_named_trigger+0xac/0xc0
   hist_register_trigger+0xc1/0x900
   event_hist_trigger_parse+0x3146/0x6af0
   event_trigger_write+0xce/0x160
  Freed by task 63:
   kfree+0x154/0x420
   trigger_kthread_fn+0xfd/0x160

Set the clock before the trigger is registered, so that nothing which
can fail runs after it is published, the way commit 6f86bdeab6
("tracing: Fix bad hist from corrupting named_triggers list") moved the
registration below the rest of the setup.

tracing_set_filter_buffering() is reference counted, so the init failure
path has to drop the reference that the clock block now takes first.

Cc: stable@vger.kernel.org
Fixes: a4072fe85b ("tracing: Add a clock attribute for hist triggers")
Link: https://patch.msgid.link/20260907091415.554535-1-donggeunyoo.kernel@gmail.com
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Donggeun Yoo 2026-09-07 18:14:15 +09:00 committed by Steven Rostedt
parent 0999d3e16d
commit 6ede78d056
1 changed files with 9 additions and 6 deletions
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15
kernel/trace/trace_events_hist.c
View File

@ -6631,12 +6631,6 @@ static int hist_register_trigger(char *glob,
data->cmd_ops = cmd_ops;
}
if (data->cmd_ops->init) {
ret = data->cmd_ops->init(data);
if (ret < 0)
goto out;
}
if (hist_data->enable_timestamps) {
char *clock = hist_data->attrs->clock;
@ -6649,6 +6643,15 @@ static int hist_register_trigger(char *glob,
tracing_set_filter_buffering(file->tr, true);
}
if (data->cmd_ops->init) {
ret = data->cmd_ops->init(data);
if (ret < 0) {
if (hist_data->enable_timestamps)
tracing_set_filter_buffering(file->tr, false);
goto out;
}
}
if (named_data) {
remove_hist_vars(hist_data);
destroy_hist_data(hist_data);