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tracing: Undo the registration when enabling the histogram trigger fails

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Commit 6f86bdeab6 ("tracing: Fix bad hist from corrupting named_triggers
list") described how a trigger that is registered but not on file->triggers
ends up freed while still on the global named_triggers list, and moved the
registration down so that hist_trigger_enable() follows it immediately. One
path still gets there. hist_trigger_enable() adds the trigger and takes it
straight back out when the event cannot be enabled:

	list_add_tail_rcu(&data->list, &file->triggers);

	update_cond_flag(file);

	if (trace_event_trigger_enable_disable(file, 1) < 0) {
		list_del_rcu(&data->list);
		update_cond_flag(file);
		ret--;
	}

so the list walk in hist_unregister_trigger() matches nothing, test stays
NULL, and the ->free() that would call del_named_trigger() is skipped.
out_unreg falls through to out_free, which frees the trigger anyway:

 BUG: KASAN: slab-use-after-free in find_named_trigger+0xac/0xc0
 Read of size 8 at addr ffff8880091d3160 by task init/1
  find_named_trigger+0xac/0xc0
  hist_register_trigger+0xc1/0xa00
  event_hist_trigger_parse+0x3146/0x6af0
  event_trigger_write+0xce/0x160
 Freed by task 69:
  kfree+0x154/0x420
  trigger_kthread_fn+0xfd/0x160

Leave the trigger where hist_unregister_trigger() can find it and let that
undo the registration, which is the only code that knows all of what
cmd_ops->init() took: the named list entry, the hist_pad reference, the
reference on the trigger a named histogram is shared with, and the copied
cmd_ops. It also pairs the failed trace_event_trigger_enable_disable(),
whose sm_ref and buffered event reference are otherwise left behind.

Since ->free() releases trigger_data and, for a trigger that does not share
its histogram, hist_data with it, out_unreg can no longer fall through to
out_free. For a trigger that does share, hist_register_trigger() has
already destroyed the caller's hist_data, so the fall-through was reading
freed memory there as well.

Move the enable_timestamps check in hist_unregister_trigger() above the
->free() call for the same reason: hist_data does not outlive it once the
trigger being removed is the one that owns it.

Cc: stable@vger.kernel.org
Fixes: 067fe038e7 ("tracing: Add variable reference handling to hist triggers")
Reported-by: Sashiko AI <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/linux-trace-kernel/20260907092944.3950E1F00A3D@smtp.kernel.org/
Link: https://patch.msgid.link/20260907124420.607097-3-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 21:44:20 +09:00 committed by Steven Rostedt
parent 0fe23b8eab
commit 92383cef66
1 changed files with 10 additions and 7 deletions
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17
kernel/trace/trace_events_hist.c
View File

@ -6670,11 +6670,12 @@ static int hist_trigger_enable(struct event_trigger_data *data,
update_cond_flag(file);
if (trace_event_trigger_enable_disable(file, 1) < 0) {
list_del_rcu(&data->list);
update_cond_flag(file);
/*
* On failure the caller undoes the registration, and
* hist_unregister_trigger() can only find the trigger here.
*/
if (trace_event_trigger_enable_disable(file, 1) < 0)
ret--;
}
return ret;
}
@ -6752,13 +6753,13 @@ static void hist_unregister_trigger(char *glob,
}
}
if (test && test->cmd_ops->free)
test->cmd_ops->free(test);
if (hist_data->enable_timestamps) {
if (!hist_data->remove || test)
tracing_set_filter_buffering(file->tr, false);
}
if (test && test->cmd_ops->free)
test->cmd_ops->free(test);
}
static bool hist_file_check_refs(struct trace_event_file *file)
@ -6963,6 +6964,8 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops,
return ret;
out_unreg:
event_trigger_unregister(cmd_ops, file, glob+1, trigger_data);
/* The unregister frees trigger_data, skip out_free */
goto out;
out_free:
remove_hist_vars(hist_data);