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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,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 AE251C43460 for ; Mon, 12 Apr 2021 06:07:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8184A61209 for ; Mon, 12 Apr 2021 06:07:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230453AbhDLGHh (ORCPT ); Mon, 12 Apr 2021 02:07:37 -0400 Received: from mail.loongson.cn ([114.242.206.163]:54486 "EHLO loongson.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S229482AbhDLGHf (ORCPT ); Mon, 12 Apr 2021 02:07:35 -0400 Received: from [10.130.0.55] (unknown [113.200.148.30]) by mail.loongson.cn (Coremail) with SMTP id AQAAf9Ax7ch343NgF_kGAA--.9298S3; Mon, 12 Apr 2021 14:06:47 +0800 (CST) Subject: Re: [PATCH] MIPS: Fix strnlen_user access check To: Tiezhu Yang , Thomas Bogendoerfer References: <1618139092-4018-1-git-send-email-hejinyang@loongson.cn> Cc: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org From: Jinyang He Message-ID: <16899466-cc3c-3b7f-0e3d-f79549185a4a@loongson.cn> Date: Mon, 12 Apr 2021 14:06:42 +0800 User-Agent: Mozilla/5.0 (X11; Linux mips64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID: AQAAf9Ax7ch343NgF_kGAA--.9298S3 X-Coremail-Antispam: 1UD129KBjvJXoWxCrykKryruFWfWw1fCFW3Wrg_yoW5XF15pF Z3A3Z7GF4DKry3AF1ay3yIqF15Gws5Gr4UK3WjgrykZr4DZr13tr4fKr1F9348JrZ7Aa4x WFy8trn8Gr4jv3DanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvv14x267AKxVWUJVW8JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26r4j6ryUM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4j 6F4UM28EF7xvwVC2z280aVAFwI0_Cr1j6rxdM28EF7xvwVC2z280aVCY1x0267AKxVW0oV Cq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0 I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Gr0_Cr1lOx8S6xCaFVCjc4AY6r1j6r 4UM4x0Y48IcVAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwCYjI0SjxkI62AI1cAE67vI Y487MxkIecxEwVAFwVW8AwCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8Jw C20s026c02F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAF wI0_JF0_Jw1lIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjx v20xvEc7CjxVAFwI0_Jr0_Gr1lIxAIcVCF04k26cxKx2IYs7xG6rW3Jr0E3s1lIxAIcVC2 z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVWUJVW8JbIYCTnIWIevJa73Uj IFyTuYvjfUjD73UUUUU X-CM-SenderInfo: pkhmx0p1dqwqxorr0wxvrqhubq/ Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/12/2021 11:02 AM, Tiezhu Yang wrote: > On 04/11/2021 07:04 PM, Jinyang He wrote: >> Commit 04324f44cb69 ("MIPS: Remove get_fs/set_fs") brought a problem for >> strnlen_user(). Jump out when checking access_ok() with condition that >> (s + strlen(s)) < __UA_LIMIT <= (s + n). The old __strnlen_user_asm() >> just checked (ua_limit & s) without checking (ua_limit & (s + n)). >> Therefore, find strlen form s to __UA_LIMIT - 1 in that condition. >> >> Signed-off-by: Jinyang He >> --- >> arch/mips/include/asm/uaccess.h | 11 +++++++++-- >> 1 file changed, 9 insertions(+), 2 deletions(-) >> >> diff --git a/arch/mips/include/asm/uaccess.h >> b/arch/mips/include/asm/uaccess.h >> index 91bc7fb..85ba0c8 100644 >> --- a/arch/mips/include/asm/uaccess.h >> +++ b/arch/mips/include/asm/uaccess.h >> @@ -630,8 +630,15 @@ static inline long strnlen_user(const char >> __user *s, long n) >> { >> long res; >> - if (!access_ok(s, n)) >> - return -0; >> + if (unlikely(n <= 0)) >> + return 0; >> + >> + if (!access_ok(s, n)) { >> + if (!access_ok(s, 0)) >> + return 0; >> + >> + n = __UA_LIMIT - (unsigned long)s - 1; >> + } >> might_fault(); >> __asm__ __volatile__( > > The following simple changes are OK to fix this issue? > > diff --git a/arch/mips/include/asm/uaccess.h > b/arch/mips/include/asm/uaccess.h > index 91bc7fb..eafc99b 100644 > --- a/arch/mips/include/asm/uaccess.h > +++ b/arch/mips/include/asm/uaccess.h > @@ -630,8 +630,8 @@ static inline long strnlen_user(const char __user > *s, long n) > { > long res; > > - if (!access_ok(s, n)) > - return -0; > + if (!access_ok(s, 1)) > + return 0; > > might_fault(); > __asm__ __volatile__( > > Thanks, > Tiezhu > Thanks for your comment. That looks similar to other archs, but I don't know how the access_ok() implementation in other archs. Using access_ok(s, 0) is similar to the old strnlen_user(). Using access_ok(s, 1) may have a problem in this extreme case, s = __UA_LIMIT - 1, *s = 0, and we hope it returns 1. But it returns 0 by !access_ok(s, 1). Of course, it is so extrme. More importantly, I want to set up a maximum for strnlen_user_asm. And do not access the part of beyond __ua_limit. As follow shows, +-----------+ | ... | +-----------+ <---- s + n | 0 | +-----------+ | s | +-----------+ | r | +-----------+ | e | +-----------+ | h | +-----------+ | t | +-----------+ | o | +-----------+ <---- __UA_LIMIT | r | +-----------+ | t | +-----------+ | s | +-----------+ <---- s | ... | +-----------+ It is dangerous to access "others", for user, only "str" is safe. I don't know whether it would be happend, I just limited it by change `n`. Should do other things if meet __UA_LIMIT - 1? Thanks, Jinyang