FAILED: patch "[PATCH] tracing: Undo the registration when enabling the histogram" 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 92383cef66791a0c63a2f27755cadbdb2fbf270b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026091612-blazer-ambiguity-e8df@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 92383cef66791a0c63a2f27755cadbdb2fbf270b Mon Sep 17 00:00:00 2001
From: Donggeun Yoo <[email protected]>
Date: Mon, 7 Sep 2026 21:44:20 +0900
Subject: [PATCH] tracing: Undo the registration when enabling the histogram
trigger fails

Commit 6f86bdeab633 ("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.

index 54c95f9bd0a3..53100287466f 100644
@@ -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);
 

From: Donggeun Yoo <[email protected]>

[ Upstream commit 92383cef66791a0c63a2f27755cadbdb2fbf270b ]

Commit 6f86bdeab633 ("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.

---
 kernel/trace/trace_events_hist.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

index 32f9ab82a8810..b501b5b00bf0b 100644
@@ -5545,11 +5545,12 @@ 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;
 }

@@ -5628,13 +5629,13 @@ static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
 		}
 	}
 
-	if (unregistered && test->ops->free)
-		test->ops->free(test->ops, test);
-
 	if (hist_data->enable_timestamps) {
 		if (!hist_data->remove || unregistered)
 			tracing_set_time_stamp_abs(file->tr, false);
 	}
+
+	if (unregistered && test->ops->free)
+		test->ops->free(test->ops, test);
 }
 
 static bool hist_file_check_refs(struct trace_event_file *file)

@@ -5833,8 +5834,11 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 		goto out_unreg;
 enable:
 	ret = hist_trigger_enable(trigger_data, file);
-	if (ret)
-		goto out_unreg;
+	if (ret) {
+		cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
+		/* The unregister frees trigger_data, skip out_free */
+		goto out;
+	}
 
 	se_name = trace_event_name(file->event_call);
 	se = find_synth_event(se_name);

2.53.0