From: Eric Dumazet <edumazet@google.com>
Date: Sun, 30 Sep 2018 11:33:39 -0700
Subject: ipv4: fix use-after-free in ip_cmsg_recv_dstaddr()
Git-commit: 64199fc0a46ba211362472f7f942f900af9492fd
Patch-mainline: v4.19-rc7
References: git-fixes

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/ipv4/ip_sockglue.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -146,7 +146,6 @@ static void ip_cmsg_recv_security(struct
 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;
 
@@ -161,7 +160,7 @@ static void ip_cmsg_recv_dstaddr(struct
 	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));