linux-kernel - Re: [PATCH 2/4] ipc/shm.c: check for overflows of shm

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Date:	Wed, 23 Apr 2014 06:58:48 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
CC:	mtk.manpages@...il.com, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	gthelen@...gle.com, aswin@...com, linux-mm@...ck.org
Subject: Re: [PATCH 2/4] ipc/shm.c: check for overflows of shm_tot

On 04/21/2014 04:26 PM, Manfred Spraul wrote:
> shm_tot counts the total number of pages used by shm segments.
> 
> If SHMALL is ULONG_MAX (or nearly ULONG_MAX), then the number
> can overflow.  Subsequent calls to shmctl(,SHM_INFO,) would return
> wrong values for shm_tot.
> 
> The patch adds a detection for overflows.
> 
> Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
> ---
>  ipc/shm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 382e2fb..2dfa3d6 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -493,7 +493,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
>  	if (size < SHMMIN || size > ns->shm_ctlmax)
>  		return -EINVAL;
>  
> -	if (ns->shm_tot + numpages > ns->shm_ctlall)
> +	if (ns->shm_tot + numpages < ns->shm_tot ||
> +			ns->shm_tot + numpages > ns->shm_ctlall)
>  		return -ENOSPC;
>  
>  	shp = ipc_rcu_alloc(sizeof(*shp));
> 

Acked-by: Michael Kerrisk <mtk.manpages@...il.com>

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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