From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755642AbZBFVak (ORCPT ); Fri, 6 Feb 2009 16:30:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753243AbZBFVab (ORCPT ); Fri, 6 Feb 2009 16:30:31 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:57893 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752551AbZBFVaa (ORCPT ); Fri, 6 Feb 2009 16:30:30 -0500 Date: Fri, 6 Feb 2009 13:29:50 -0800 From: Andrew Morton To: Guennadi Liakhovetski Cc: linux-kernel@vger.kernel.org, lethal@linux-sh.org, adrian@newgolddream.dyndns.info, lkmladrian@gmail.com, linux-sh@vger.kernel.org, penberg@cs.helsinki.fi, dbaryshkov@gmail.com, penguin-kernel@i-love.sakura.ne.jp, hannes@cmpxchg.org Subject: Re: [PATCH] fix broken size test in bitmap_find_free_region() Message-Id: <20090206132950.96c3f92e.akpm@linux-foundation.org> In-Reply-To: References: <8b67d60901201348r6a59928dw3fcf8c9c823d5c68@mail.gmail.com> <1232488507.6794.8.camel@localhost.localdomain> <20090121033951.GB14094@linux-sh.org> <20090121081118.GA14537@linux-sh.org> <20090127134831.3dd04182.akpm@linux-foundation.org> <20090127225458.GA8756@linux-sh.org> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 6 Feb 2009 13:22:33 +0100 (CET) Guennadi Liakhovetski wrote: > This loop and test in bitmap_find_free_region() > > for (pos = 0; pos < bits; pos += (1 << order)) > if (__reg_op(bitmap, pos, order, REG_OP_ISFREE)) > break; > if (pos == bits) > return -ENOMEM; > > can only return an error (-ENOMEM) if bits is a multiple of (1 << order), > which is, for instance, true, if bits is (also) a power of 2. This > is not necessarily the case with dma_alloc_from_coherent(). A failure to > recognise too large a request leads in dma_alloc_from_coherent() to > accessing beyond available memory, and to writing beyond the bitmap. > Do we have any reports of dma_alloc_from_coherent() actually behaving in that way? > --- > > diff --git a/lib/bitmap.c b/lib/bitmap.c > index 1338469..d49c37f 100644 > --- a/lib/bitmap.c > +++ b/lib/bitmap.c > @@ -953,7 +953,7 @@ int bitmap_find_free_region(unsigned long *bitmap, int bits, int order) > for (pos = 0; pos < bits; pos += (1 << order)) > if (__reg_op(bitmap, pos, order, REG_OP_ISFREE)) > break; > - if (pos == bits) > + if (pos + (1 << order) > bits) > return -ENOMEM; > __reg_op(bitmap, pos, order, REG_OP_ALLOC); > return pos;