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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 45D18C33CB3 for ; Wed, 15 Jan 2020 12:54:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2561A206D7 for ; Wed, 15 Jan 2020 12:54:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729106AbgAOMyi (ORCPT ); Wed, 15 Jan 2020 07:54:38 -0500 Received: from mx2.suse.de ([195.135.220.15]:58658 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726100AbgAOMyh (ORCPT ); Wed, 15 Jan 2020 07:54:37 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 96AD3AD2D; Wed, 15 Jan 2020 12:54:34 +0000 (UTC) Subject: Re: [PATCH] mm/mempolicy.c: Fix out of bounds write in mpol_parse_str() To: Dan Carpenter , Andrew Morton , Lee Schermerhorn Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot , aarcange@redhat.com, hughd@google.com, mhocko@suse.com, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, yang.shi@linux.alibaba.com References: <20200115055426.vdjwvry44nfug7yy@kili.mountain> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 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xVKRSg3I2m+DUTVqBy7Lixo73hnW69kSjtqCeamY/NSu6LNP+b0wAOKhwz9hBEwEHLp05+mj 5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: Date: Wed, 15 Jan 2020 13:54:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <20200115055426.vdjwvry44nfug7yy@kili.mountain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/15/20 6:54 AM, Dan Carpenter wrote: > What we are trying to do is change the '=' character to a NUL terminator > and then at the end of the function we restore it back to an '='. The > problem is there are two error paths where we jump to the end of the > function before we have replaced the '=' with NUL. We end up putting > the '=' in the wrong place (possibly one element before the start of > the buffer). Bleh. > Reported-by: syzbot+e64a13c5369a194d67df@syzkaller.appspotmail.com > Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display") > Signed-off-by: Dan Carpenter Acked-by: Vlastimil Babka CC stable perhaps? Can this (tmpfs mount options parsing AFAICS?) become part of unprivileged operation in some scenarios? > --- > mm/mempolicy.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 067cf7d3daf5..1340c5c496b5 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -2817,6 +2817,9 @@ int mpol_parse_str(char *str, struct mempolicy **mpol) > char *flags = strchr(str, '='); > int err = 1, mode; > > + if (flags) > + *flags++ = '\0'; /* terminate mode string */ > + > if (nodelist) { > /* NUL-terminate mode or flags string */ > *nodelist++ = '\0'; > @@ -2827,9 +2830,6 @@ int mpol_parse_str(char *str, struct mempolicy **mpol) > } else > nodes_clear(nodes); > > - if (flags) > - *flags++ = '\0'; /* terminate mode string */ > - > mode = match_string(policy_modes, MPOL_MAX, str); > if (mode < 0) > goto out; >