From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by kanga.kvack.org (Postfix) with ESMTP id EF4048E0001 for ; Thu, 13 Sep 2018 07:11:38 -0400 (EDT) Received: by mail-wr1-f72.google.com with SMTP id u12-v6so4612580wrc.1 for ; Thu, 13 Sep 2018 04:11:38 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id n17-v6si4782193edf.195.2018.09.13.04.11.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Sep 2018 04:11:37 -0700 (PDT) Date: Thu, 13 Sep 2018 13:11:35 +0200 From: Michal Hocko Subject: Re: [PATCH] selinux: Add __GFP_NOWARN to allocation at str_read() Message-ID: <20180913111135.GA21006@dhcp22.suse.cz> References: <000000000000038dab0575476b73@google.com> <9d685700-bc5c-9c2f-7795-56f488d2ea38@sony.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9d685700-bc5c-9c2f-7795-56f488d2ea38@sony.com> Sender: owner-linux-mm@kvack.org List-ID: To: peter enderborg Cc: Tetsuo Handa , Paul Moore , selinux@tycho.nsa.gov, syzbot+ac488b9811036cea7ea0@syzkaller.appspotmail.com, Eric Paris , linux-kernel@vger.kernel.org, Stephen Smalley , syzkaller-bugs@googlegroups.com, linux-mm On Thu 13-09-18 09:12:04, peter enderborg wrote: > 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; I strongly suspect that you want kvmalloc rather than kmalloc here. The larger the request the more likely is the allocation to fail. I am not familiar with the code but I assume this is a root only interface so we don't have to worry about nasty users scenario. -- Michal Hocko SUSE Labs