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

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Message-ID: <81ecef6f-5076-873c-2f0d-e08e0a35dcf5@redhat.com>
Date:   Thu, 25 Jan 2018 22:17:38 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...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 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