[PATCH v3] appletalk: Fix Use-After-Free in atalk_ioctl

[PATCH v3] appletalk: Fix Use-After-Free in atalk_ioctl

[Hyunwoo Kim]

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>
---
v1 -> v2: Change the code style
v2 -> v3: Delete old comments
---
 net/appletalk/ddp.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 9ba04a69ec2a..a852ec093fa8 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1775,15 +1775,14 @@ 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;
 	}
-- 
2.25.1

Re: [PATCH v3] appletalk: Fix Use-After-Free in atalk_ioctl

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Tue, 12 Dec 2023 23:10:56 -0500 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [v3] appletalk: Fix Use-After-Free in atalk_ioctl
    https://git.kernel.org/netdev/net/c/189ff16722ee

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html