[PATCH net] ipv4: fix use-after-free in ip_cmsg_recv_dstaddr()

* [PATCH net] ipv4: fix use-after-free in ip_cmsg_recv_dstaddr()
@ 2018-09-30 18:33 Eric Dumazet
  2018-09-30 22:00 ` Willem de Bruijn
  2018-10-03  5:32 ` David Miller
  0 siblings, 2 replies; 3+ messages in thread
From: Eric Dumazet @ 2018-09-30 18:33 UTC (permalink / raw)
  To: David S . Miller; +Cc: netdev, Eric Dumazet, Eric Dumazet, Willem de Bruijn

Caching ip_hdr(skb) before a call to pskb_may_pull() is buggy,
do not do it.

Fixes: 2efd4fca703a ("ip: in cmsg IP(V6)_ORIGDSTADDR call pskb_may_pull")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
---
 net/ipv4/ip_sockglue.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index c0fe5ad996f238091f5b9585adb586a571f653f0..26c36cccabdc2c8cc95cfd609672d412c493fc42 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -149,7 +149,6 @@ static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb)
 static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct sk_buff *skb)
 {
 	struct sockaddr_in sin;
-	const struct iphdr *iph = ip_hdr(skb);
 	__be16 *ports;
 	int end;
 
@@ -164,7 +163,7 @@ static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct sk_buff *skb)
 	ports = (__be16 *)skb_transport_header(skb);
 
 	sin.sin_family = AF_INET;
-	sin.sin_addr.s_addr = iph->daddr;
+	sin.sin_addr.s_addr = ip_hdr(skb)->daddr;
 	sin.sin_port = ports[1];
 	memset(sin.sin_zero, 0, sizeof(sin.sin_zero));
 
-- 
2.19.0.605.g01d371f741-goog

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