[PATCH 4.9 17/54] net/packet: fix overflow in tpacket_rcv

[Greg Kroah-Hartman]

From: Or Cohen <orcohen@xxxxxxxxxxxxxxxxxxxx>

commit acf69c946233259ab4d64f8869d4037a198c7f06 upstream.

Using tp_reserve to calculate netoff can overflow as
tp_reserve is unsigned int and netoff is unsigned short.

This may lead to macoff receving a smaller value then
sizeof(struct virtio_net_hdr), and if po->has_vnet_hdr
is set, an out-of-bounds write will occur when
calling virtio_net_hdr_from_skb.

The bug is fixed by converting netoff to unsigned int
and checking if it exceeds USHRT_MAX.

This addresses CVE-2020-14386

Fixes: 8913336a7e8d ("packet: add PACKET_RESERVE sockopt")
Signed-off-by: Or Cohen <orcohen@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[ snu: backported to pre-5.3, changed tp_drops counting/locking ]
Signed-off-by: Stefan Nuernberger <snu@xxxxxxxxxx>
CC: David Woodhouse <dwmw@xxxxxxxxxxxx>
CC: Amit Shah <aams@xxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/packet/af_packet.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2161,7 +2161,8 @@ static int tpacket_rcv(struct sk_buff *s
 	int skb_len = skb->len;
 	unsigned int snaplen, res;
 	unsigned long status = TP_STATUS_USER;
-	unsigned short macoff, netoff, hdrlen;
+	unsigned short macoff, hdrlen;
+	unsigned int netoff;
 	struct sk_buff *copy_skb = NULL;
 	struct timespec ts;
 	__u32 ts_status;
@@ -2223,6 +2224,12 @@ static int tpacket_rcv(struct sk_buff *s
 		}
 		macoff = netoff - maclen;
 	}
+	if (netoff > USHRT_MAX) {
+		spin_lock(&sk->sk_receive_queue.lock);
+		po->stats.stats1.tp_drops++;
+		spin_unlock(&sk->sk_receive_queue.lock);
+		goto drop_n_restore;
+	}
 	if (po->tp_version <= TPACKET_V2) {
 		if (macoff + snaplen > po->rx_ring.frame_size) {
 			if (po->copy_thresh &&