bareudp: Fix invalid read beyond skb's linear data

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@redhat.com>
Link: https://lore.kernel.org/r/7741c46545c6ef02e70c80a9b32814b22d9616b3.1628264975.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/bareudp.c b/drivers/net/bareudp.c
index a7ee0af..54e321a 100644 (file)
--- 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++;