linux-kernel - Re: [PATCH v4] rcu-tasks: Fix show_rcu_tasks_trace_gp

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Date: Wed, 27 Mar 2024 13:52:46 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Nikita Kiryushin <kiryushin@...ud.ru>
Cc: "Paul E. McKenney" <paulmck@...nel.org>, Frederic Weisbecker
 <frederic@...nel.org>, Neeraj Upadhyay <quic_neeraju@...cinc.com>, Joel
 Fernandes <joel@...lfernandes.org>, Josh Triplett <josh@...htriplett.org>,
 Boqun Feng <boqun.feng@...il.com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Lai Jiangshan <jiangshanlai@...il.com>,
 Zqiang <qiang.zhang1211@...il.com>, rcu@...r.kernel.org,
 linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH v4] rcu-tasks: Fix show_rcu_tasks_trace_gp_kthread
 buffer overflow

On Wed, 27 Mar 2024 20:47:47 +0300
Nikita Kiryushin <kiryushin@...ud.ru> wrote:

> 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().
> 

Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve

> 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@...ud.ru>
> ---
> v4: Change ARRAY_SIZE to sizeof() as more idiomatic
> as Steven Rostedt <rostedt@...dmis.org> suggested
> v3: Fixed commit message
> v2: Use snprintf() as
> Steven Rostedt <rostedt@...dmis.org> suggested.
>  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 147b5945d67a..2a453de9f3d9 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -1994,7 +1994,7 @@ void show_rcu_tasks_trace_gp_kthread(void)
>  {
>  	char buf[64];
>  
> -	sprintf(buf, "N%lu h:%lu/%lu/%lu",
> +	snprintf(buf, sizeof(buf), "N%lu h:%lu/%lu/%lu",
>  		data_race(n_trc_holdouts),
>  		data_race(n_heavy_reader_ofl_updates),
>  		data_race(n_heavy_reader_updates),