[PATCH AUTOSEL 6.1 04/12] tracing/user_events: Fix the incorrect trace record for empty arguments events

[Sasha Levin]

From: sunliming <sunliming@xxxxxxxxxx>

[ Upstream commit 6f05dcabe5c241d066ec472cf38ac8b84f8c9c6f ]

The user_events support events that has empty arguments. But the trace event
is discarded and not really committed when the arguments is empty. Fix this
by not attempting to copy in zero-length data.

Link: https://lkml.kernel.org/r/20230606062027.1008398-2-sunliming@xxxxxxxxxx

Acked-by: Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx>
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: sunliming <sunliming@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/trace/trace_events_user.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index ad64da21c34aa..49e114d250136 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -916,7 +916,7 @@ static void user_event_ftrace(struct user_event *user, struct iov_iter *i,
 	if (unlikely(!entry))
 		return;
 
-	if (unlikely(!copy_nofault(entry + 1, i->count, i)))
+	if (unlikely(i->count != 0 && !copy_nofault(entry + 1, i->count, i)))
 		goto discard;
 
 	if (!list_empty(&user->validators) &&
@@ -957,7 +957,7 @@ static void user_event_perf(struct user_event *user, struct iov_iter *i,
 
 		perf_fetch_caller_regs(regs);
 
-		if (unlikely(!copy_nofault(perf_entry + 1, i->count, i)))
+		if (unlikely(i->count != 0 && !copy_nofault(perf_entry + 1, i->count, i)))
 			goto discard;
 
 		if (!list_empty(&user->validators) &&
-- 
2.39.2