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

Orabug: 25813773
CVE: CVE-2017-7308

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.

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 2b6867c2ce76c596676bec7d2d525af525fdc6e2)
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 0b86b605f9043fc08cf7ceb2b28fa236c7c6615c..4b1bc45290045da67fd4831f92fd5d3d002919ba 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3866,8 +3866,8 @@ 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))