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 BA51BC04ABB for ; Thu, 13 Sep 2018 07:12:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6F4E320C0A for ; Thu, 13 Sep 2018 07:12:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F4E320C0A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=sony.com 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 S1727655AbeIMMUR convert rfc822-to-8bit (ORCPT ); Thu, 13 Sep 2018 08:20:17 -0400 Received: from seldsegrel01.sonyericsson.com ([37.139.156.29]:3057 "EHLO SELDSEGREL01.sonyericsson.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726694AbeIMMUR (ORCPT ); Thu, 13 Sep 2018 08:20:17 -0400 Subject: Re: [PATCH] selinux: Add __GFP_NOWARN to allocation at str_read() To: Tetsuo Handa , Paul Moore CC: , , Eric Paris , , Stephen Smalley , , linux-mm References: <000000000000038dab0575476b73@google.com> From: peter enderborg Message-ID: <9d685700-bc5c-9c2f-7795-56f488d2ea38@sony.com> Date: Thu, 13 Sep 2018 09:12:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/13/2018 08:26 AM, Tetsuo Handa wrote: > On 2018/09/13 12:02, Paul Moore wrote: >> On Fri, Sep 7, 2018 at 12:43 PM Tetsuo Handa >> wrote: >>> syzbot is hitting warning at str_read() [1] because len parameter can >>> become larger than KMALLOC_MAX_SIZE. We don't need to emit warning for >>> this case. >>> >>> [1] https://syzkaller.appspot.com/bug?id=7f2f5aad79ea8663c296a2eedb81978401a908f0 >>> >>> Signed-off-by: Tetsuo Handa >>> Reported-by: syzbot >>> --- >>> security/selinux/ss/policydb.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c >>> index e9394e7..f4eadd3 100644 >>> --- a/security/selinux/ss/policydb.c >>> +++ b/security/selinux/ss/policydb.c >>> @@ -1101,7 +1101,7 @@ static int str_read(char **strp, gfp_t flags, void *fp, u32 len) >>> if ((len == 0) || (len == (u32)-1)) >>> return -EINVAL; >>> >>> - str = kmalloc(len + 1, flags); >>> + str = kmalloc(len + 1, flags | __GFP_NOWARN); >>> if (!str) >>> return -ENOMEM; >> Thanks for the patch. >> >> My eyes are starting to glaze over a bit chasing down all of the >> different kmalloc() code paths trying to ensure that this always does >> the right thing based on size of the allocation and the different slab >> allocators ... are we sure that this will always return NULL when (len >> + 1) is greater than KMALLOC_MAX_SIZE for the different slab allocator >> configurations? >> > Yes, for (len + 1) cannot become 0 (which causes kmalloc() to return > ZERO_SIZE_PTR) due to (len == (u32)-1) check above. > > The only concern would be whether you want allocation failure messages. > I assumed you don't need it because we are returning -ENOMEM to the caller. > Would it not be better with     char *str;     if ((len == 0) || (len == (u32)-1) || (len >= KMALLOC_MAX_SIZE))         return -EINVAL;     str = kmalloc(len + 1, flags);     if (!str)         return -ENOMEM;