netdev - [Patch net] netrom: fix locking in nr_find

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Date:   Sat, 29 Dec 2018 13:56:38 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>
Subject: [Patch net] netrom: fix locking in nr_find_socket()

nr_find_socket(), nr_find_peer() and nr_find_listener() lock the
sock after finding it in the global list. However, the call path
requires BH disabled for the sock lock consistently.

Actually the locking is unnecessary at this point, we can just hold
the sock refcnt to make sure it is not gone after we unlock the global
list, and lock it later only when needed.

Reported-and-tested-by: syzbot+f621cda8b7e598908efa@...kaller.appspotmail.com
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/netrom/af_netrom.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/netrom/af_netrom.c b/net/netrom/af_netrom.c
index 03f37c4e64fe..1d3144d19903 100644
--- a/net/netrom/af_netrom.c
+++ b/net/netrom/af_netrom.c
@@ -153,7 +153,7 @@ static struct sock *nr_find_listener(ax25_address *addr)
 	sk_for_each(s, &nr_list)
 		if (!ax25cmp(&nr_sk(s)->source_addr, addr) &&
 		    s->sk_state == TCP_LISTEN) {
-			bh_lock_sock(s);
+			sock_hold(s);
 			goto found;
 		}
 	s = NULL;
@@ -174,7 +174,7 @@ static struct sock *nr_find_socket(unsigned char index, unsigned char id)
 		struct nr_sock *nr = nr_sk(s);
 
 		if (nr->my_index == index && nr->my_id == id) {
-			bh_lock_sock(s);
+			sock_hold(s);
 			goto found;
 		}
 	}
@@ -198,7 +198,7 @@ static struct sock *nr_find_peer(unsigned char index, unsigned char id,
 
 		if (nr->your_index == index && nr->your_id == id &&
 		    !ax25cmp(&nr->dest_addr, dest)) {
-			bh_lock_sock(s);
+			sock_hold(s);
 			goto found;
 		}
 	}
@@ -224,7 +224,7 @@ static unsigned short nr_find_next_circuit(void)
 		if (i != 0 && j != 0) {
 			if ((sk=nr_find_socket(i, j)) == NULL)
 				break;
-			bh_unlock_sock(sk);
+			sock_put(sk);
 		}
 
 		id++;
@@ -920,6 +920,7 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	if (sk != NULL) {
+		bh_lock_sock(sk);
 		skb_reset_transport_header(skb);
 
 		if (frametype == NR_CONNACK && skb->len == 22)
@@ -929,6 +930,7 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 
 		ret = nr_process_rx_frame(sk, skb);
 		bh_unlock_sock(sk);
+		sock_put(sk);
 		return ret;
 	}
 
@@ -960,10 +962,12 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 	    (make = nr_make_new(sk)) == NULL) {
 		nr_transmit_refusal(skb, 0);
 		if (sk)
-			bh_unlock_sock(sk);
+			sock_put(sk);
 		return 0;
 	}
 
+	bh_lock_sock(sk);
+
 	window = skb->data[20];
 
 	skb->sk             = make;
@@ -1016,6 +1020,7 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 		sk->sk_data_ready(sk);
 
 	bh_unlock_sock(sk);
+	sock_put(sk);
 
 	nr_insert_socket(make);
 
-- 
2.19.2