linux-kernel - Re: [PATCH v2] exec: avoid gcc-8 warning for get_task

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Date:   Wed, 6 Dec 2017 18:49:34 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <james.l.morris@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <asarai@...e.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] exec: avoid gcc-8 warning for get_task_comm


* Arnd Bergmann <arnd@...db.de> wrote:

> gcc-8 warns about using strncpy() with the source size as the limit:
> 
> fs/exec.c:1223:32: error: argument to 'sizeof' in 'strncpy' call is the same expression as the source; did you mean to use the size of the destination? [-Werror=sizeof-pointer-memaccess]
> 
> This is indeed slightly suspicious, as it protects us from source
> arguments without NUL-termination, but does not guarantee that the
> destination is terminated.
> 
> This keeps the strncpy() to ensure we have properly padded target buffer,
> but ensures that we use the correct length, by passing the actual length
> of the destination buffer as well as adding a build-time check to ensure
> it is exactly TASK_COMM_LEN.  There are only 23 callsights which I all
> reviewed to ensure this is currently the case. We could get away with
> doing only the check or passing the right length, but it doesn't hurt
> to do both.
> 
> Suggested-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Looks useful.

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo