netdev - Re: [PATCH net-next] ptr_ring: fix integer overflow

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Message-ID: <20180125193131-mutt-send-email-mst@kernel.org>
Date:   Thu, 25 Jan 2018 19:31:48 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH net-next] ptr_ring: fix integer overflow

On Thu, Jan 25, 2018 at 10:17:38PM +0800, Jason Wang wrote:
> 
> 
> On 2018年01月25日 21:45, Michael S. Tsirkin wrote:
> > On Thu, Jan 25, 2018 at 03:31:42PM +0800, Jason Wang wrote:
> > > We try to allocate one more entry for lockless peeking. The adding
> > > operation may overflow which causes zero to be passed to kmalloc().
> > > In this case, it returns ZERO_SIZE_PTR without any notice by ptr
> > > ring. Try to do producing or consuming on such ring will lead NULL
> > > dereference. Fix this detect and fail early.
> > > 
> > > Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
> > > Reported-by:syzbot+87678bcf753b44c39b67@...kaller.appspotmail.com
> > > Cc: John Fastabend<john.fastabend@...il.com>
> > > Signed-off-by: Jason Wang<jasowang@...hat.com>
> > Ugh that's just way too ugly.
> > I'll work on dropping the extra + 1 - but calling this
> > function with -1 size is the real source of the bug.
> > Do you know how come we do that?
> > 
> 
> It looks e.g try to change tx_queue_len to UINT_MAX. And we probably can't
> prevent user form trying to do this?
> 
> Thanks

Right. BTW why net-next? Isn't the crash exploitable in net?