[PATCH 4.14 12/26] appletalk: Fix Use-After-Free in atalk_ioctl

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hyunwoo Kim <v4bel@theori.io>

[ Upstream commit 189ff16722ee36ced4d2a2469d4ab65a8fee4198 ]

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
Link: https://lore.kernel.org/r/20231213041056.GA519680@v4bel-B760M-AORUS-ELITE-AX
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/appletalk/ddp.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1810,15 +1810,14 @@ static int atalk_ioctl(struct socket *so
 		break;
 	}
 	case TIOCINQ: {
-		/*
-		 * These two are safe on a single CPU system as only
-		 * user tasks fiddle here
-		 */
-		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
+		struct sk_buff *skb;
 		long amount = 0;
 
+		spin_lock_irq(&sk->sk_receive_queue.lock);
+		skb = skb_peek(&sk->sk_receive_queue);
 		if (skb)
 			amount = skb->len - sizeof(struct ddpehdr);
+		spin_unlock_irq(&sk->sk_receive_queue.lock);
 		rc = put_user(amount, (int __user *)argp);
 		break;
 	}