[PATCH net] netlink: reset extack earlier in netlink_rcv_skb

[Xin Long]

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+03bee3680a3746677...@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/netlink/af_netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 47ef2d8..84a4e4c 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2391,6 +2391,7 @@ int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct 
sk_buff *,
        while (skb->len >= nlmsg_total_size(0)) {
                int msglen;
 
+               memset(&extack, 0, sizeof(extack));
                nlh = nlmsg_hdr(skb);
                err = 0;
 
@@ -2405,7 +2406,6 @@ int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct 
sk_buff *,
                if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
                        goto ack;
 
-               memset(&extack, 0, sizeof(extack));
                err = cb(skb, nlh, &extack);
                if (err == -EINTR)
                        goto skip;
-- 
2.1.0