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Date:   Wed, 6 Dec 2017 15:09:20 -0800
From:   Kees Cook <>
To:     Ingo Molnar <>
Cc:     Arnd Bergmann <>,
        Alexander Viro <>,
        Ingo Molnar <>,
        Peter Zijlstra <>,
        Serge Hallyn <>,
        James Morris <>,
        Andrew Morton <>,
        Aleksa Sarai <>,
        "Eric W. Biederman" <>,
        Frederic Weisbecker <>,
        Thomas Gleixner <>,
        "" <>,
        LKML <>
Subject: Re: [PATCH v2] exec: avoid gcc-8 warning for get_task_comm

On Wed, Dec 6, 2017 at 9:49 AM, Ingo Molnar <> wrote:
> * Arnd Bergmann <> 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 <>
>> Signed-off-by: Arnd Bergmann <>
> Looks useful.
> Acked-by: Ingo Molnar <>

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


Kees Cook
Pixel Security

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