rcu-tasks: Fix show_rcu_tasks_trace_gp_kthread buffer overflow

mainline inclusion
from mainline-v6.10-rc1
commit cc5645fddb0ce28492b15520306d092730dffa48
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IA6SGB
CVE: CVE-2024-38577

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=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: edf3775f ("rcu-tasks: Add count for idle tasks on offline CPUs")
Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>