From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Iwai Subject: Re: [PATCH] ALSA: isa: gus: Fix a possible null-pointer dereference in snd_gf1_mem_xfree() Date: Tue, 23 Jul 2019 15:47:47 +0200 Message-ID: References: <20190723134020.25972-1-baijiaju1990@gmail.com> Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <20190723134020.25972-1-baijiaju1990@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Jia-Ju Bai Cc: huangfq.daxian@gmail.com, tglx@linutronix.de, allison@lohutok.net, perex@perex.cz, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org List-Id: alsa-devel@alsa-project.org On Tue, 23 Jul 2019 15:40:20 +0200, Jia-Ju Bai wrote: > > In snd_gf1_mem_xfree(), there is an if statement on line 72 and line 74 > to check whether block->next is NULL: > if (block->next) > > When block->next is NULL, block->next is used on line 84: > block->next->prev = block->prev; > > Thus, a possible null-pointer dereference may occur in this case. There is already a check beforehand: if (alloc->last == block) { and the code path you're referring to is only after this check fails, i.e. it's no last entry, hence block->next can be never NULL. So the current code is OK. thanks, Takashi > > To fix this possible bug, block->next is checked before using it. > > This bug is found by a static analysis tool STCheck written by us. > > Signed-off-by: Jia-Ju Bai > --- > sound/isa/gus/gus_mem.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/sound/isa/gus/gus_mem.c b/sound/isa/gus/gus_mem.c > index cb02d18dde60..ed6205b88057 100644 > --- a/sound/isa/gus/gus_mem.c > +++ b/sound/isa/gus/gus_mem.c > @@ -81,7 +81,8 @@ int snd_gf1_mem_xfree(struct snd_gf1_mem * alloc, struct snd_gf1_mem_block * blo > if (block->prev) > block->prev->next = NULL; > } else { > - block->next->prev = block->prev; > + if (block->next) > + block->next->prev = block->prev; > if (block->prev) > block->prev->next = block->next; > } > -- > 2.17.0 > > 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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 4099DC41517 for ; Tue, 23 Jul 2019 13:47:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2393A218DA for ; Tue, 23 Jul 2019 13:47:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390391AbfGWNrt (ORCPT ); Tue, 23 Jul 2019 09:47:49 -0400 Received: from mx2.suse.de ([195.135.220.15]:39306 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726260AbfGWNrt (ORCPT ); Tue, 23 Jul 2019 09:47:49 -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 1BCF6AF7E; Tue, 23 Jul 2019 13:47:48 +0000 (UTC) Date: Tue, 23 Jul 2019 15:47:47 +0200 Message-ID: From: Takashi Iwai To: "Jia-Ju Bai" Cc: , , , , , Subject: Re: [PATCH] ALSA: isa: gus: Fix a possible null-pointer dereference in snd_gf1_mem_xfree() In-Reply-To: <20190723134020.25972-1-baijiaju1990@gmail.com> References: <20190723134020.25972-1-baijiaju1990@gmail.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/25.3 (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 Tue, 23 Jul 2019 15:40:20 +0200, Jia-Ju Bai wrote: > > In snd_gf1_mem_xfree(), there is an if statement on line 72 and line 74 > to check whether block->next is NULL: > if (block->next) > > When block->next is NULL, block->next is used on line 84: > block->next->prev = block->prev; > > Thus, a possible null-pointer dereference may occur in this case. There is already a check beforehand: if (alloc->last == block) { and the code path you're referring to is only after this check fails, i.e. it's no last entry, hence block->next can be never NULL. So the current code is OK. thanks, Takashi > > To fix this possible bug, block->next is checked before using it. > > This bug is found by a static analysis tool STCheck written by us. > > Signed-off-by: Jia-Ju Bai > --- > sound/isa/gus/gus_mem.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/sound/isa/gus/gus_mem.c b/sound/isa/gus/gus_mem.c > index cb02d18dde60..ed6205b88057 100644 > --- a/sound/isa/gus/gus_mem.c > +++ b/sound/isa/gus/gus_mem.c > @@ -81,7 +81,8 @@ int snd_gf1_mem_xfree(struct snd_gf1_mem * alloc, struct snd_gf1_mem_block * blo > if (block->prev) > block->prev->next = NULL; > } else { > - block->next->prev = block->prev; > + if (block->next) > + block->next->prev = block->prev; > if (block->prev) > block->prev->next = block->next; > } > -- > 2.17.0 > >