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* [PATCH net] net/packet: fix overflow in tpacket_rcv
@ 2020-09-04  4:05 Eric Dumazet
  0 siblings, 0 replies; only message in thread
From: Eric Dumazet @ 2020-09-04  4:05 UTC (permalink / raw)
  To: David S . Miller
  Cc: netdev, Eric Dumazet, Linus Torvalds, Eric Dumazet, Or Cohen

From: Or Cohen <orcohen@paloaltonetworks.com>

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@paloaltonetworks.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/packet/af_packet.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 479c257ded7335616da35aa5f7880b54aa2f9fe0..1377a485d45109da8e5f241ff8f64d4f37180592 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2170,7 +2170,8 @@ 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 timespec64 ts;
 	__u32 ts_status;
@@ -2239,6 +2240,10 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 		}
 		macoff = netoff - maclen;
 	}
+	if (netoff > USHRT_MAX) {
+		atomic_inc(&po->tp_drops);
+		goto drop_n_restore;
+	}
 	if (po->tp_version <= TPACKET_V2) {
 		if (macoff + snaplen > po->rx_ring.frame_size) {
 			if (po->copy_thresh &&
-- 
2.28.0.526.ge36021eeef-goog


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2020-09-04  4:05 [PATCH net] net/packet: fix overflow in tpacket_rcv Eric Dumazet

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