linux-kernel - Re: [PATCH 1/7] fs/exec: make __set_task_comm always set a nul terminated string

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Message-ID: <c3571571-320a-3e25-8409-5653ddca895c@redhat.com>
Date:   Wed, 10 Nov 2021 09:28:12 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Yafang Shao <laoar.shao@...il.com>, akpm@...ux-foundation.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        oliver.sang@...el.com, lkp@...el.com,
        Kees Cook <keescook@...omium.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH 1/7] fs/exec: make __set_task_comm always set a nul
 terminated string

On 08.11.21 09:38, Yafang Shao wrote:
> Make sure the string set to task comm is always nul terminated.
> 

strlcpy: "the result is always a valid NUL-terminated string that fits
in the buffer"

The only difference seems to be that strscpy_pad() pads the remainder
with zeroes.

Is this description correct and I am missing something important?

> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: Michal Miroslaw <mirq-linux@...e.qmqm.pl> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Petr Mladek <pmladek@...e.com>
> ---
>  fs/exec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index a098c133d8d7..404156b5b314 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1224,7 +1224,7 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
>  {
>  	task_lock(tsk);
>  	trace_task_rename(tsk, buf);
> -	strlcpy(tsk->comm, buf, sizeof(tsk->comm));
> +	strscpy_pad(tsk->comm, buf, sizeof(tsk->comm));
>  	task_unlock(tsk);
>  	perf_event_comm(tsk, exec);
>  }
> 


-- 
Thanks,

David / dhildenb