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

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Date:   Wed, 6 Dec 2017 15:09:20 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.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-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] exec: avoid gcc-8 warning for get_task_comm

On Wed, Dec 6, 2017 at 9:49 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * 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>

Ingo, can you take this into -tip, or should this go via -mm or some other tree?

-Kees

-- 
Kees Cook
Pixel Security