[bionic:linux, bionic:linux-hwe-5.0][PATCH] UBUNTU: SAUCE: net/packet: fix overflow in tpacket_rcv

[Marcelo Henrique Cerri]

From: Or Cohen <orcohen at paloaltonetworks.com>

CVE-2020-14386

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 at paloaltonetworks.com>
Signed-off-by: Eric Dumazet <edumazet at google.com>

[ snu: backported to 4.9, changed tp_drops counting/locking ]

Signed-off-by: Stefan Nuernberger <snu at amazon.com>
CC: David Woodhouse <dwmw at amazon.co.uk>
CC: Amit Shah <aams at amazon.com>
CC: stable at vger.kernel.org

[ mhcerri: from the netdev mailing list:
  https://lore.kernel.org/netdev/CAM6JnLf_8nwzq+UGO+amXpeApCDarJjwzOEHQd5qBhU7YKm3DQ@mail.gmail.com/
  This is the fixed proposed on the mailing list for 4.9, this fix
  should be intended to any kernel that doesn't have commit id 8e8e2951e309
  ("net/packet: make tp_drops atomic"). For us, that means any kernel
  before 5.3.
  Tested with the reproducer proposed by the author.]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 net/packet/af_packet.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 89d6b0957d07..cd5fbec69de8 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2160,7 +2160,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 	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 *skb, struct net_device *dev,
 		}
 		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 &&
-- 
2.25.1