FAILED: patch "[PATCH] tracing: Fix trace_marker copy link list updates" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 07183aac4a6828e474f00b37c9d795d0d99e18a7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026032336-exhale-bounce-7a32@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 07183aac4a6828e474f00b37c9d795d0d99e18a7 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <[email protected]>
Date: Wed, 18 Mar 2026 18:55:12 -0400
Subject: [PATCH] tracing: Fix trace_marker copy link list updates

When the "copy_trace_marker" option is enabled for an instance, anything written into /sys/kernel/tracing/trace_marker is also copied into that instances buffer. When the option is set, that instance's trace_array descriptor is added to the marker_copies link list. This list is protected by RCU, as all iterations uses an RCU protected list traversal.

When the instance is deleted, all the flags that were enabled are cleared. This also clears the copy_trace_marker flag and removes the trace_array descriptor from the list.

The issue is after the flags are called, a direct call to update_marker_trace() is performed to clear the flag. This function returns true if the state of the flag changed and false otherwise. If it returns true here, synchronize_rcu() is called to make sure all readers see that its removed from the list.

But since the flag was already cleared, the state does not change and the synchronization is never called, leaving a possible UAF bug.

Move the clearing of all flags below the updating of the copy_trace_marker option which then makes sure the synchronization is performed.

Also use the flag for checking the state in update_marker_trace() instead of looking at if the list is empty.

index bb4a62f4b953..a626211ceb9a 100644
@@ -555,7 +555,7 @@ static bool update_marker_trace(struct trace_array *tr, int enabled)
 	lockdep_assert_held(&event_mutex);
 
 	if (enabled) {
-		if (!list_empty(&tr->marker_list))
+		if (tr->trace_flags & TRACE_ITER(COPY_MARKER))
 			return false;
 
 		list_add_rcu(&tr->marker_list, &marker_copies);

@@ -563,10 +563,10 @@ static bool update_marker_trace(struct trace_array *tr, int enabled)
 		return true;
 	}
 
-	if (list_empty(&tr->marker_list))
+	if (!(tr->trace_flags & TRACE_ITER(COPY_MARKER)))
 		return false;
 
-	list_del_init(&tr->marker_list);
+	list_del_rcu(&tr->marker_list);
 	tr->trace_flags &= ~TRACE_ITER(COPY_MARKER);
 	return true;
 }

@@ -9761,18 +9761,19 @@ static int __remove_instance(struct trace_array *tr)
 
 	list_del(&tr->list);
 
+	if (printk_trace == tr)
+		update_printk_trace(&global_trace);
+
+	/* Must be done before disabling all the flags */
+	if (update_marker_trace(tr, 0))
+		synchronize_rcu();
+
 	/* Disable all the flags that were enabled coming in */
 	for (i = 0; i < TRACE_FLAGS_MAX_SIZE; i++) {
 		if ((1ULL << i) & ZEROED_TRACE_FLAGS)
 			set_tracer_flag(tr, 1ULL << i, 0);
 	}
 
-	if (printk_trace == tr)
-		update_printk_trace(&global_trace);
-
-	if (update_marker_trace(tr, 0))
-		synchronize_rcu();
-
 	tracing_set_nop(tr);
 	clear_ftrace_function_probes(tr);
 	event_trace_del_tracer(tr);

From: Steven Rostedt <[email protected]>

[ Upstream commit 07183aac4a6828e474f00b37c9d795d0d99e18a7 ]

When the "copy_trace_marker" option is enabled for an instance, anything written into /sys/kernel/tracing/trace_marker is also copied into that instances buffer. When the option is set, that instance's trace_array descriptor is added to the marker_copies link list. This list is protected by RCU, as all iterations uses an RCU protected list traversal.

When the instance is deleted, all the flags that were enabled are cleared. This also clears the copy_trace_marker flag and removes the trace_array descriptor from the list.

The issue is after the flags are called, a direct call to update_marker_trace() is performed to clear the flag. This function returns true if the state of the flag changed and false otherwise. If it returns true here, synchronize_rcu() is called to make sure all readers see that its removed from the list.

But since the flag was already cleared, the state does not change and the synchronization is never called, leaving a possible UAF bug.

Move the clearing of all flags below the updating of the copy_trace_marker option which then makes sure the synchronization is performed.

Also use the flag for checking the state in update_marker_trace() instead of looking at if the list is empty.

---
 kernel/trace/trace.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

index ff5d0b6d52e03..b5f88fcfd4ddc 100644
@@ -569,7 +569,7 @@ static bool update_marker_trace(struct trace_array *tr, int enabled)
 	lockdep_assert_held(&event_mutex);
 
 	if (enabled) {
-		if (!list_empty(&tr->marker_list))
+		if (tr->trace_flags & TRACE_ITER_COPY_MARKER)
 			return false;
 
 		list_add_rcu(&tr->marker_list, &marker_copies);

@@ -577,10 +577,10 @@ static bool update_marker_trace(struct trace_array *tr, int enabled)
 		return true;
 	}
 
-	if (list_empty(&tr->marker_list))
+	if (!(tr->trace_flags & TRACE_ITER_COPY_MARKER))
 		return false;
 
-	list_del_init(&tr->marker_list);
+	list_del_rcu(&tr->marker_list);
 	tr->trace_flags &= ~TRACE_ITER_COPY_MARKER;
 	return true;
 }

@@ -10215,18 +10215,19 @@ static int __remove_instance(struct trace_array *tr)
 
 	list_del(&tr->list);
 
-	/* Disable all the flags that were enabled coming in */
-	for (i = 0; i < TRACE_FLAGS_MAX_SIZE; i++) {
-		if ((1 << i) & ZEROED_TRACE_FLAGS)
-			set_tracer_flag(tr, 1 << i, 0);
-	}
-
 	if (printk_trace == tr)
 		update_printk_trace(&global_trace);
 
+	/* Must be done before disabling all the flags */
 	if (update_marker_trace(tr, 0))
 		synchronize_rcu();
 
+	/* Disable all the flags that were enabled coming in */
+	for (i = 0; i < TRACE_FLAGS_MAX_SIZE; i++) {
+		if ((1 << i) & ZEROED_TRACE_FLAGS)
+			set_tracer_flag(tr, 1 << i, 0);
+	}
+
 	tracing_set_nop(tr);
 	clear_ftrace_function_probes(tr);
 	event_trace_del_tracer(tr);

2.51.0