udp: fix a race in encap_rcv handling

udp_queue_rcv_skb() has a possible race in encap_rcv handling, since
this pointer can be changed anytime.

We should use ACCESS_ONCE() to close the race.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 131d8a720086f89f426c89e4caa1720fa31751f7..ab0966df1e2a8aec9e4ecb40e77332cbebbde466 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1397,6 +1397,8 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
        nf_reset(skb);
 
        if (up->encap_type) {
+               int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
+
                /*
                 * This is an encapsulation socket so pass the skb to
                 * the socket's udp_encap_rcv() hook. Otherwise, just
@@ -1409,11 +1411,11 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
                 */
 
                /* if we're overly short, let UDP handle it */
-               if (skb->len > sizeof(struct udphdr) &&
-                   up->encap_rcv != NULL) {
+               encap_rcv = ACCESS_ONCE(up->encap_rcv);
+               if (skb->len > sizeof(struct udphdr) && encap_rcv != NULL) {
                        int ret;
 
-                       ret = (*up->encap_rcv)(sk, skb);
+                       ret = encap_rcv(sk, skb);
                        if (ret <= 0) {
                                UDP_INC_STATS_BH(sock_net(sk),
                                                 UDP_MIB_INDATAGRAMS,