From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id 2A2F96B004F for ; Thu, 12 Jan 2012 16:58:05 -0500 (EST) Date: Thu, 12 Jan 2012 13:58:03 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: Don't warn if memdup_user fails Message-Id: <20120112135803.1fb98fd6.akpm@linux-foundation.org> In-Reply-To: References: <1326300636-29233-1-git-send-email-levinsasha928@gmail.com> <20120111141219.271d3a97.akpm@linux-foundation.org> <1326355594.1999.7.camel@lappy> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Pekka Enberg , Sasha Levin , lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Tyler Hicks , Dustin Kirkland , ecryptfs@vger.kernel.org On Thu, 12 Jan 2012 13:19:54 -0800 (PST) David Rientjes wrote: > On Thu, 12 Jan 2012, Pekka Enberg wrote: > > > I think you missed Andrew's point. We absolutely want to issue a > > kernel warning here because ecryptfs is misusing the memdup_user() > > API. We must not let userspace processes allocate large amounts of > > memory arbitrarily. > > > > I think it's good to fix ecryptfs like Tyler is doing and, at the same > time, ensure that the len passed to memdup_user() makes sense prior to > kmallocing memory with GFP_KERNEL. Perhaps something like > > if (WARN_ON(len > PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) > return ERR_PTR(-ENOMEM); > > in which case __GFP_NOWARN is irrelevant. If someone is passing huge size_t's into kmalloc() and getting failures then that's probably a bug. So perhaps we should add a warning to kmalloc itself if the size_t is out of bounds, and !__GFP_NOWARN. That might cause problems with those callers who like to call kmalloc() in a probing loop with decreasing size_t. But none of this will be very effective. If someone is passing an unchecked size_t into kmalloc then normal testing will not reveal the problem because the testers won't pass stupid numbers into their syscalls. -- 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