From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE557ECDE5F for ; Thu, 19 Jul 2018 09:11:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 728932084C for ; Thu, 19 Jul 2018 09:11:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 728932084C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730921AbeGSJx3 (ORCPT ); Thu, 19 Jul 2018 05:53:29 -0400 Received: from mx2.suse.de ([195.135.220.15]:38474 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726975AbeGSJx2 (ORCPT ); Thu, 19 Jul 2018 05:53:28 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 910ECADB3; Thu, 19 Jul 2018 09:11:14 +0000 (UTC) Date: Thu, 19 Jul 2018 11:11:14 +0200 Message-ID: From: Takashi Iwai To: "Zhang, Jun" Cc: "He, Bo" , "alsa-devel@alsa-project.org" , "perex@perex.cz" , "linux-kernel@vger.kernel.org" , "Zhang, Yanmin" Subject: Re: [PATCH] ALSA: core: fix unsigned int pages overflow when comapred In-Reply-To: References: <88DC34334CA3444C85D647DBFA962C272B0C4C34@SHSMSX104.ccr.corp.intel.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/26 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 19 Jul 2018 08:42:14 +0200, Takashi Iwai wrote: > > On Thu, 19 Jul 2018 08:08:06 +0200, > Zhang, Jun wrote: > > > > Hello, Takashi > > > > I think use our patch, it's NOT possible that the returned size is over sgbuf->tblsize. > > > > In function snd_malloc_sgbuf_pages, > > > > Pages is align page, > > sgbuf->tblsize is align 32*page, > > chunk is align 2^n*page, > > > > in our panic case, pages = 123, tlbsize = 128, > > 1st loop trunk = 32 > > 2nd loop trunk = 32 > > 3rd loop trunk = 32 > > 4th loop trunk = 16 > > 5th loop trunk = 16 > > So in 5th loop pages-trunk = -5, which make dead loop. > > Looking at the code again, yeah, you are right, that won't happen. > > And now it becomes clear: the fundamental problem is that > snd_dma_alloc_pages_fallback() returns a larger size than requested. > It would be acceptable if the internal allocator aligns a larger size, > but it shouldn't appear in the returned size outside. I believe this > was just a misunderstanding of get_order() usage there. > (BTW, it's interesting that the allocation with a larger block worked > while allocation with a smaller chunk failed; it must be a rare case > and that's one of reasons this bug didn't hit frequently.) > > That being said, what we should fix is rather the function > snd_dma_alloc_pages_fallback() to behave as expected, and it'll be > like the patch below. And we can reduce even more lines. A proper patch is below. thanks, Takashi -- 8< -- From: Takashi Iwai Subject: [PATCH] ALSA: memalloc: Don't exceed over the requested size snd_dma_alloc_pages_fallback() tries to allocate pages again when the allocation fails with reduced size. But the first try actually *increases* the size to power-of-two, which may give back a larger chunk than the requested size. This confuses the callers, e.g. sgbuf assumes that the size is equal or less, and it may result in a bad loop due to the underflow and eventually lead to Oops. The code of this function seems incorrectly assuming the usage of get_order(). We need to decrease at first, then align to power-of-two. Reported-by: he, bo Reported-by: zhang jun Cc: Signed-off-by: Takashi Iwai --- sound/core/memalloc.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c index 7f89d3c79a4b..753d5fc4b284 100644 --- a/sound/core/memalloc.c +++ b/sound/core/memalloc.c @@ -242,16 +242,12 @@ int snd_dma_alloc_pages_fallback(int type, struct device *device, size_t size, int err; while ((err = snd_dma_alloc_pages(type, device, size, dmab)) < 0) { - size_t aligned_size; if (err != -ENOMEM) return err; if (size <= PAGE_SIZE) return -ENOMEM; - aligned_size = PAGE_SIZE << get_order(size); - if (size != aligned_size) - size = aligned_size; - else - size >>= 1; + size >>= 1; + size = PAGE_SIZE << get_order(size); } if (! dmab->area) return -ENOMEM; -- 2.18.0