bridge: fix a possible use after free

[ Upstream commit 22df13319d1fec30b8f9bcaadc295829647109bb ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 4 deletions

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 22d2d1af1c8..995cbe0ac0b 100644
--- 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;