[PATCH v5.10-v5.15] rcu-tasks: Fix show_rcu_tasks_trace_gp_kthread buffer overflow

[Vamsi Krishna Brahmajosyula]

From: Nikita Kiryushin <kiryushin@xxxxxxxx>

[ Upstream commit cc5645fddb0ce28492b15520306d092730dffa48 ]

There is a possibility of buffer overflow in
show_rcu_tasks_trace_gp_kthread() if counters, passed
to sprintf() are huge. Counter numbers, needed for this
are unrealistically high, but buffer overflow is still
possible.

Use snprintf() with buffer size instead of sprintf().

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: edf3775f0ad6 ("rcu-tasks: Add count for idle tasks on offline CPUs")
Signed-off-by: Nikita Kiryushin <kiryushin@xxxxxxxx>
Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
Signed-off-by: Vamsi Krishna Brahmajosyula <vamsi-krishna.brahmajosyula@xxxxxxxxxxxx>
---
 kernel/rcu/tasks.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 105fdc2bb004..bede3a4f108e 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1240,7 +1240,7 @@ static void show_rcu_tasks_trace_gp_kthread(void)
 {
 	char buf[64];
 
-	sprintf(buf, "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end),
+	snprintf(buf, sizeof(buf), "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end),
 		data_race(n_heavy_reader_ofl_updates),
 		data_race(n_heavy_reader_updates),
 		data_race(n_heavy_reader_attempts));
-- 
2.45.2