From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx197.postini.com [74.125.245.197]) by kanga.kvack.org (Postfix) with SMTP id CD0A86B13F0 for ; Tue, 14 Feb 2012 03:52:56 -0500 (EST) Date: Tue, 14 Feb 2012 00:53:01 -0800 From: Andrew Morton Subject: Re: [PATCH] slab: warning if total alloc size overflow Message-Id: <20120214005301.a9d5be1a.akpm@linux-foundation.org> In-Reply-To: <1329204499-2671-1-git-send-email-hamo.by@gmail.com> References: <1329204499-2671-1-git-send-email-hamo.by@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Yang Bai Cc: cl@linux-foundation.org, penberg@kernel.org, mpm@selenic.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, 14 Feb 2012 15:28:19 +0800 Yang Bai wrote: > Before, if the total alloc size is overflow, > we just return NULL like alloc fail. But they > are two different type problems. The former looks > more like a programming problem. So add a warning > here. > > Signed-off-by: Yang Bai > --- > include/linux/slab.h | 4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 573c809..5865237 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -242,8 +242,10 @@ size_t ksize(const void *); > */ > static inline void *kcalloc(size_t n, size_t size, gfp_t flags) > { > - if (size != 0 && n > ULONG_MAX / size) > + if (size != 0 && n > ULONG_MAX / size) { > + WARN(1, "Alloc memory size (%lu * %lu) overflow.", n, size); > return NULL; > + } > return __kmalloc(n * size, flags | __GFP_ZERO); > } One of the applications of kcalloc() is to prevent userspace from causing a multiplicative overflow (and then perhaps causing an overwrite beyond the end of the allocated memory). With this patch, we've just handed the user a way of spamming the logs at 1MHz. This is bad. Also, please let's not randomly add debug stuff in places where we've never demonstrated a need for it. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org