Re: [netfilter-core] kernel panic: Out of memory and no killable processes... (2)

Florian Westphal
2018-01-29T07:27:07Z

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?