From: Xin Long <lucien.xin@gmail.com>
Date: Thu, 18 Jan 2018 14:48:03 +0800
Subject: netlink: reset extack earlier in netlink_rcv_skb
Git-commit: cd443f1e91ca600a092e780e8250cd6a2954b763
Patch-mainline: v4.15-rc9
References: networking-stable-18_01_28

Move up the extack reset/initialization in netlink_rcv_skb, so that
those 'goto ack' will not skip it. Otherwise, later on netlink_ack
may use the uninitialized extack and cause kernel crash.

Fixes: cbbdf8433a5f ("netlink: extack needs to be reset each time through loop")
Reported-by: syzbot+03bee3680a37466775e7@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/netlink/af_netlink.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2392,6 +2392,7 @@ int netlink_rcv_skb(struct sk_buff *skb,
 	while (skb->len >= nlmsg_total_size(0)) {
 		int msglen;
 
+		memset(&extack, 0, sizeof(extack));
 		nlh = nlmsg_hdr(skb);
 		err = 0;
 
@@ -2406,7 +2407,6 @@ int netlink_rcv_skb(struct sk_buff *skb,
 		if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
 			goto ack;
 
-		memset(&extack, 0, sizeof(extack));
 		err = cb(skb, nlh, &extack);
 		if (err == -EINTR)
 			goto skip;