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

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Date:   Fri, 26 Jan 2018 11:44:22 +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26日 01:31, Michael S. Tsirkin wrote:
> 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?
>

Commit bcecb4bbf88a exists only in net-next. And in net we check r->size 
before trying to dereference the queue.

Thanks