appletalk: Fix Use-After-Free in atalk_ioctl

[ 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>

diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 8978fb6..b070a89 100644 (file)
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1811,15 +1811,14 @@ static int atalk_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
                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;
        }