net/packet: fix overflow in check for tp_frame_nr

net/packet: fix overflow in check for tp_frame_nr

Orabug: 25813773
CVE: CVE-2017-7308

When calculating rb->frames_per_block * req->tp_block_nr the result
can overflow.

Add a check that tp_block_size * tp_block_nr <= UINT_MAX.

Since frames_per_block <= tp_block_size, the expression would
never overflow.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 8f8d28e4d6d815a391285e121c3a53a0b6cb9e7b)
Signed-off-by: Brian Maly <brian.maly@oracle.com>