tracing/trigger: Fix to return error if failed to alloc snapshot

JIRA: https://issues.redhat.com/browse/RHEL-33284
CVE: CVE-2024-26920

commit b5085b5
Author: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Date:   Fri Jan 26 09:42:58 2024 +0900

    tracing/trigger: Fix to return error if failed to alloc snapshot

    commit 0958b33 upstream.

    Fix register_snapshot_trigger() to return error code if it failed to
    allocate a snapshot instead of 0 (success). Unless that, it will register
    snapshot trigger without an error.

    Link: https://lore.kernel.org/linux-trace-kernel/170622977792.270660.2789298642759362200.stgit@devnote2

    Fixes: 0bbe7f7 ("tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation")
    Cc: stable@vger.kernel.org
    Cc: Vincent Donnefort <vdonnefort@google.com>
    Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Author: jeromemarchand

kernel/trace/trace_events_trigger.c

@@ -1108,8 +1108,10 @@ register_snapshot_trigger(char *glob, struct event_trigger_ops *ops,
 			  struct event_trigger_data *data,
 			  struct trace_event_file *file)
 {
-	if (tracing_alloc_snapshot_instance(file->tr) != 0)
-		return 0;
+	int ret = tracing_alloc_snapshot_instance(file->tr);
+
+	if (ret < 0)
+		return ret;
 
 	return register_trigger(glob, ops, data, file);
 }