linux-kernel - Re: [PATCH] kmemleak: avoid buffer overrun: NUL-terminate strncpy-copied command

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Date:	Fri, 24 Aug 2012 11:27:26 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Jim Meyering <jim@...ering.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jim Meyering <meyering@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] kmemleak: avoid buffer overrun: NUL-terminate
 strncpy-copied command

On Mon, Aug 20, 2012 at 05:55:22PM +0100, Jim Meyering wrote:
> From: Jim Meyering <meyering@...hat.com>
> 
> strncpy NUL-terminates only when the length of the source string
> is smaller than the size of the destination buffer.
> The two other strncpy uses (just preceding) happen to be ok
> with the current TASK_COMM_LEN (16), because the literals
> "hardirq" and "softirq" are both shorter than 16.  However,
> technically it'd be better to use strcpy along with a
> compile-time assertion that they fit in the buffer.
> 
> Signed-off-by: Jim Meyering <meyering@...hat.com>
> ---
>  mm/kmemleak.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 45eb621..947257f 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -555,6 +555,7 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
>  		 * case, the command line is not correct.
>  		 */
>  		strncpy(object->comm, current->comm, sizeof(object->comm));
> +		object->comm[sizeof(object->comm) - 1] = 0;

Does it really matter here? object->comm[] and current->comm[] have the
same size, TASK_COMM_LEN.

-- 
Catalin
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