bridge: fix a possible use after free

br_multicast_ipv6_rcv() can call pskb_trim_rcsum() and therefore skb
head can be reallocated.

Cache icmp6_type field instead of dereferencing twice the struct
icmp6hdr pointer.

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

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 22d2d1af1c8347f05aba5d3076a7cb971df6357f..995cbe0ac0b2b1e74f2b4762d61a13102d9f66bb 100644 (file)
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1456,7 +1456,7 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 {
        struct sk_buff *skb2;
        const struct ipv6hdr *ip6h;
-       struct icmp6hdr *icmp6h;
+       u8 icmp6_type;
        u8 nexthdr;
        unsigned len;
        int offset;
@@ -1502,9 +1502,9 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
        __skb_pull(skb2, offset);
        skb_reset_transport_header(skb2);
 
-       icmp6h = icmp6_hdr(skb2);
+       icmp6_type = icmp6_hdr(skb2)->icmp6_type;
 
-       switch (icmp6h->icmp6_type) {
+       switch (icmp6_type) {
        case ICMPV6_MGM_QUERY:
        case ICMPV6_MGM_REPORT:
        case ICMPV6_MGM_REDUCTION:
@@ -1544,7 +1544,7 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 
        BR_INPUT_SKB_CB(skb)->igmp = 1;
 
-       switch (icmp6h->icmp6_type) {
+       switch (icmp6_type) {
        case ICMPV6_MGM_REPORT:
            {
                struct mld_msg *mld;