Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 29 Jan 2018 08:23:57 +0100
From:   Florian Westphal <fw@strlen.de>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     davem@davemloft.net, netfilter-devel@vger.kernel.org,
        coreteam@netfilter.org, netdev@vger.kernel.org,
        aarcange@redhat.com, yang.s@alibaba-inc.com, mhocko@suse.com,
        syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org,
        mingo@kernel.org, linux-mm@kvack.org, rientjes@google.com,
        akpm@linux-foundation.org, guro@fb.com,
        kirill.shutemov@linux.intel.com
Subject: Re: [netfilter-core] kernel panic: Out of memory and no killable
 processes... (2)
Message-ID: <20180129072357.GD5906@breakpoint.cc>
References: <001a1144b0caee2e8c0563d9de0a@google.com>
 <201801290020.w0T0KK8V015938@www262.sakura.ne.jp>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <201801290020.w0T0KK8V015938@www262.sakura.ne.jp>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote:
> syzbot wrote:
> > syzbot hit the following crash on net-next commit
> > 6bb46bc57c8e9ce947cc605e555b7204b44d2b10 (Fri Jan 26 16:00:23 2018 +0000)
> > Merge branch 'cxgb4-fix-dump-collection-when-firmware-crashed'
> > 
> > C reproducer is attached.
> > syzkaller reproducer is attached.
> > Raw console output is attached.
> > compiler: gcc (GCC) 7.1.1 20170620
> > .config is attached.
> > 
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+8630e35fc7287b392aac@syzkaller.appspotmail.com
> > It will help syzbot understand when the bug is fixed. See footer for  
> > details.
> > If you forward the report, please keep this part and the footer.
> > 
> > [ 3685]     0  3685    17821        1   184320        0             0 sshd
> > [ 3692]     0  3692     4376        0    32768        0             0  
> > syzkaller025682
> > [ 3695]     0  3695     4376        0    36864        0             0  
> > syzkaller025682
> > Kernel panic - not syncing: Out of memory and no killable processes...
> > 
> 
> This sounds like too huge vmalloc() request where size is controlled by userspace.

Right.

Before eacd86ca3b036e55e172b7279f101cef4a6ff3a4
this used 

              info = __vmalloc(sz, GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY,

would it help to re-add that?

> vmalloc() once became killable by commit 5d17a73a2ebeb8d1 ("vmalloc: back
> off when the current task is killed") but then became unkillable by commit
> b8c8a338f75e052d ("Revert "vmalloc: back off when the current task is
> killed""). Therefore, we can't handle this problem from MM side.
> Please consider adding some limit from networking side.

I don't know what "some limit" would be.  I would prefer if there was
a way to supress OOM Killer in first place so we can just -ENOMEM user.

AFAIU NOWARN|NORETRY does that, so I would propose to just read-add it?