linux-kernel - [190/244] bridge: fix a possible use after free

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Date:	Wed, 28 Sep 2011 15:02:34 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [190/244] bridge: fix a possible use after free

3.0-stable review patch.  If anyone has any objections, please let us know.

------------------


From: Eric Dumazet <eric.dumazet@...il.com>

[ 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@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 net/bridge/br_multicast.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1456,7 +1456,7 @@ static int br_multicast_ipv6_rcv(struct
 {
 	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
 	__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
 
 	BR_INPUT_SKB_CB(skb)->igmp = 1;
 
-	switch (icmp6h->icmp6_type) {
+	switch (icmp6_type) {
 	case ICMPV6_MGM_REPORT:
 	    {
 		struct mld_msg *mld;


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