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

From: Jason Wang
Date: Thu Jan 25 2018 - 09:17:53 EST




On 2018å01æ25æ 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@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: John Fastabend<john.fastabend@xxxxxxxxx>
Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>
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