From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: [PATCH] bcache: fix BUG_ON due to integer overflow with GC_SECTORS_USED Date: Tue, 11 Feb 2014 10:18:05 -0800 Message-ID: <20140211181805.GA11655@kmo> References: <20140211180257.GA26313@kmo> <20140211181431.GA19110@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pb0-f43.google.com ([209.85.160.43]:52308 "EHLO mail-pb0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751986AbaBKSSI (ORCPT ); Tue, 11 Feb 2014 13:18:08 -0500 Received: by mail-pb0-f43.google.com with SMTP id md12so8071472pbc.2 for ; Tue, 11 Feb 2014 10:18:07 -0800 (PST) Content-Disposition: inline In-Reply-To: <20140211181431.GA19110@kroah.com> Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: Greg KH Cc: stable@vger.kernel.org, linux-bcache@vger.kernel.org On Tue, Feb 11, 2014 at 10:14:31AM -0800, Greg KH wrote: > On Tue, Feb 11, 2014 at 10:02:57AM -0800, Darrick J. Wong wrote: > > The BUG_ON at the end of __bch_btree_mark_key can be triggered due to > > an integer overflow error: > > > > BITMASK(GC_SECTORS_USED, struct bucket, gc_mark, 2, 13); > > ... > > SET_GC_SECTORS_USED(g, min_t(unsigned, > > GC_SECTORS_USED(g) + KEY_SIZE(k), > > (1 << 14) - 1)); > > BUG_ON(!GC_SECTORS_USED(g)); > > > > In bcache.h, the SECTORS_USED bitfield is defined to be 13 bits wide. > > While the SET_ code tries to ensure that the field doesn't overflow by > > clamping it to (1<<14)-1 == 16383, this is incorrect because 16383 > > requires 14 bits. Therefore, if GC_SECTORS_USED() + KEY_SIZE() = > > 8192, the SET_ statement tries to store 8192 into a 13-bit field. In > > a 13-bit field, 8192 becomes zero, thus triggering the BUG_ON. > > > > Therefore, create a field width constant and a max value constant, and > > use those to create the bitfield and check the inputs to > > SET_GC_SECTORS_USED. Arguably the BITMASK() template ought to have > > BUG_ON checks for too-large values, but that's a separate patch. > > > > Signed-off-by: Darrick J. Wong > > Signed-off-by: Kent Overstreet > > --- > > Greg, stable team et. all - can you apply this asap to 3.13? It hasn't hit > > Linus's tree yet (it's on its way via Jens), but multiple users are hitting this > > BUG_ON() and the fix has been tested. > > Think about what you just wrote. > > Then go read Documentation/stable_kernel_rules.txt. > > You should know better... I figured if any patch qualified for skipping ahead this one would - and it always takes awhile for stuff to make it through Jens, but ah well. It's 947174476701fbc84ea8c7ec9664270f9d80b076, currently in Jens' for-linus tree, I'll ping you again when I see it go in since I forgot to add the stable tag to the patch.