ipv4: fix use-after-free in ip_cmsg_recv_dstaddr()

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>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 2 deletions

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index c0fe5ad996f2..26c36cccabdc 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));