From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf1-f71.google.com (mail-lf1-f71.google.com [209.85.167.71]) by kanga.kvack.org (Postfix) with ESMTP id 677368E0001 for ; Thu, 13 Sep 2018 15:28:59 -0400 (EDT) Received: by mail-lf1-f71.google.com with SMTP id 25-v6so2004970lfs.22 for ; Thu, 13 Sep 2018 12:28:59 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id p7-v6sor3018629ljc.18.2018.09.13.12.28.58 for (Google Transport Security); Thu, 13 Sep 2018 12:28:58 -0700 (PDT) MIME-Version: 1.0 References: <000000000000038dab0575476b73@google.com> <9d685700-bc5c-9c2f-7795-56f488d2ea38@sony.com> In-Reply-To: <9d685700-bc5c-9c2f-7795-56f488d2ea38@sony.com> From: Paul Moore Date: Thu, 13 Sep 2018 15:28:46 -0400 Message-ID: Subject: Re: [PATCH] selinux: Add __GFP_NOWARN to allocation at str_read() Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: peter.enderborg@sony.com Cc: penguin-kernel@i-love.sakura.ne.jp, selinux@tycho.nsa.gov, syzbot+ac488b9811036cea7ea0@syzkaller.appspotmail.com, Eric Paris , linux-kernel@vger.kernel.org, Stephen Smalley , syzkaller-bugs@googlegroups.com, linux-mm@kvack.org On Thu, Sep 13, 2018 at 3:12 AM 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; As long as it's safe, I'd rather leave the maximum allocation limit as a kmalloc internal and let kmalloc return NULL if we try too large of an allocation. -- paul moore www.paul-moore.com