Commit 07183aac4a68 for kernel

commit 07183aac4a6828e474f00b37c9d795d0d99e18a7
Author: Steven Rostedt <rostedt@goodmis.org>
Date:   Wed Mar 18 18:55:12 2026 -0400

    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.

    Cc: stable@vger.kernel.org
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Link: https://patch.msgid.link/20260318185512.1b6c7db4@gandalf.local.home
    Fixes: 7b382efd5e8a ("tracing: Allow the top level trace_marker to write into another instances")
    Reported-by: Sasha Levin <sashal@kernel.org>
    Closes: https://lore.kernel.org/all/20260225133122.237275-1-sashal@kernel.org/
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index bb4a62f4b953..a626211ceb9a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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);

-	/* 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);

+	/* 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);
+	}
+
 	tracing_set_nop(tr);
 	clear_ftrace_function_probes(tr);
 	event_trace_del_tracer(tr);