Re: [PATCH v2] exec: avoid gcc-8 warning for get_task_comm

From: Ingo Molnar <mingo@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	Serge Hallyn <serge@hallyn.com>,
	James Morris <james.l.morris@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Aleksa Sarai <asarai@suse.de>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] exec: avoid gcc-8 warning for get_task_comm
Date: Wed, 6 Dec 2017 18:49:34 +0100	[thread overview]
Message-ID: <20171206174934.e5s6c5dh5lscwkyp@gmail.com> (raw)
In-Reply-To: <20171205151724.1764896-1-arnd@arndb.de>

* Arnd Bergmann <arnd@arndb.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@chromium.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Looks useful.

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

Thanks,

	Ingo