[PATCH 5.13 077/151] bareudp: Fix invalid read beyond skbs linear data

[Greg Kroah-Hartman]

From: Guillaume Nault <gnault@xxxxxxxxxx>

[ Upstream commit 143a8526ab5fd4f8a0c4fe2a9cb28c181dc5a95f ]

Data beyond the UDP header might not be part of the skb's linear data.
Use skb_copy_bits() instead of direct access to skb->data+X, so that
we read the correct bytes even on a fragmented skb.

Fixes: 4b5f67232d95 ("net: Special handling for IP & MPLS.")
Signed-off-by: Guillaume Nault <gnault@xxxxxxxxxx>
Link: https://lore.kernel.org/r/7741c46545c6ef02e70c80a9b32814b22d9616b3.1628264975.git.gnault@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/bareudp.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/bareudp.c b/drivers/net/bareudp.c
index edfad93e7b68..22e26458a86e 100644
--- a/drivers/net/bareudp.c
+++ b/drivers/net/bareudp.c
@@ -71,12 +71,18 @@ static int bareudp_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
 		family = AF_INET6;
 
 	if (bareudp->ethertype == htons(ETH_P_IP)) {
-		struct iphdr *iphdr;
+		__u8 ipversion;
 
-		iphdr = (struct iphdr *)(skb->data + BAREUDP_BASE_HLEN);
-		if (iphdr->version == 4) {
-			proto = bareudp->ethertype;
-		} else if (bareudp->multi_proto_mode && (iphdr->version == 6)) {
+		if (skb_copy_bits(skb, BAREUDP_BASE_HLEN, &ipversion,
+				  sizeof(ipversion))) {
+			bareudp->dev->stats.rx_dropped++;
+			goto drop;
+		}
+		ipversion >>= 4;
+
+		if (ipversion == 4) {
+			proto = htons(ETH_P_IP);
+		} else if (ipversion == 6 && bareudp->multi_proto_mode) {
 			proto = htons(ETH_P_IPV6);
 		} else {
 			bareudp->dev->stats.rx_dropped++;
-- 
2.30.2