[PATCH v2] net/rose: Fix Use-After-Free in rose_ioctl

[Hyunwoo Kim <v4bel@theori.io>]

Because rose_ioctl() accesses sk->sk_receive_queue
without holding a sk->sk_receive_queue.lock, it can
cause a race with rose_accept().
A use-after-free for skb occurs with the following flow.
```
rose_ioctl() -> skb_peek()
rose_accept() -> skb_dequeue() -> kfree_skb()
```
Add sk->sk_receive_queue.lock to rose_ioctl() to fix this issue.

Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
---
v1 -> v2: Use sk->sk_receive_queue.lock instead of lock_sock.
---
 net/rose/af_rose.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index 0cc5a4e19900..841c238de222 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -1316,8 +1316,10 @@ static int rose_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 		struct sk_buff *skb;
 		long amount = 0L;
 		/* These two are safe on a single CPU system as only user tasks fiddle here */
+		spin_lock(&sk->sk_receive_queue.lock);
 		if ((skb = skb_peek(&sk->sk_receive_queue)) != NULL)
 			amount = skb->len;
+		spin_unlock(&sk->sk_receive_queue.lock);
 		return put_user(amount, (unsigned int __user *) argp);
 	}
 
-- 
2.25.1