net/packet: fix overflow in check for priv area size

Subtracting tp_sizeof_priv from tp_block_size and casting to int
to check whether one is less then the other doesn't always work
(both of them are unsigned ints).

Compare them as is instead.

Also cast tp_sizeof_priv to u64 before using BLK_PLUS_PRIV, as
it can overflow inside BLK_PLUS_PRIV otherwise.

Change-Id: I6ea9173654eb07b0135045c9825b2d6fe1bf3978
Signed-off-by: Andrey Konovalov <[email protected]>
Acked-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Git-commit: 2b6867c2ce76c596676bec7d2d525af525fdc6e2
Signed-off-by: Dennis Cagle <[email protected]>
Signed-off-by: Francisco Franco <[email protected]>

net/packet/af_packet.c

@@ -3661,8 +3661,8 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
 		if (unlikely(req->tp_block_size & (PAGE_SIZE - 1)))
 			goto out;
 		if (po->tp_version >= TPACKET_V3 &&
-		    (int)(req->tp_block_size -
-			  BLK_PLUS_PRIV(req_u->req3.tp_sizeof_priv)) <= 0)
+		    req->tp_block_size <=
+			  BLK_PLUS_PRIV((u64)req_u->req3.tp_sizeof_priv))
 			goto out;
 		if (unlikely(req->tp_frame_size < po->tp_hdrlen +
 					po->tp_reserve))