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.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
BugLink: https://bugs.launchpad.net/bugs/1678009
CVE-2017-7308
(cherry picked from commit 2b6867c2ce76c596676bec7d2d525af525fdc6e2 linux-net)
Signed-off-by: Andy Whitcroft <apw@canonical.com>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index f223d1c80ccf7f9251dce0f8f31f58c766576946..937f26e9ba028776f543c589455141c2e83d9a4a 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4115,8 +4115,8 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
                if (unlikely(!PAGE_ALIGNED(req->tp_block_size)))
                        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))