[Patch net] netrom: hold sock when setting skb->destructor

[Cong Wang]

sock_efree() releases the sock refcnt, if we don't hold this refcnt
when setting skb->destructor to it, the refcnt would not be balanced.
This leads to several bug reports from syzbot.

I have checked other users of sock_efree(), all of them hold the
sock refcnt.

Fixes: c8c8218ec5af ("netrom: fix a memory leak in nr_rx_frame()")
Reported-and-tested-by: <syzbot+622bdabb128acc334...@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+6eaef7158b19e3fec...@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+9399c158fcc09b21d...@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+a34e5f3d0300163f0...@syzkaller.appspotmail.com>
Cc: Ralf Baechle <r...@linux-mips.org>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 net/netrom/af_netrom.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/netrom/af_netrom.c b/net/netrom/af_netrom.c
index 96740d389377..c4f54ad2b98a 100644
--- a/net/netrom/af_netrom.c
+++ b/net/netrom/af_netrom.c
@@ -967,6 +967,7 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 
        window = skb->data[20];
 
+       sock_hold(make);
        skb->sk             = make;
        skb->destructor     = sock_efree;
        make->sk_state      = TCP_ESTABLISHED;
-- 
2.21.0