[PATCH v3] net/x25: Fix to not accept on connected socket

[PATCH v3] net/x25: Fix to not accept on connected socket

[Hyunwoo Kim]

If you call listen() and accept() on an already connect()ed
x25 socket, accept() can successfully connect.
This is because when the peer socket sends data to sendmsg,
the skb with its own sk stored in the connected socket's
sk->sk_receive_queue is connected, and x25_accept() dequeues
the skb waiting in the sk->sk_receive_queue.

This creates a child socket with the sk of the parent
x25 socket, which can cause confusion.

Fix x25_listen() to return -EINVAL if the socket has
already been successfully connected, and add lock_sock
to prevent this issue.

Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
v1 -> v2 : Change the flag to check to SS_UNCONNECTED
v2 -> v3 : Fix wrong patch description
---
 net/x25/af_x25.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 3b55502b2965..5c7ad301d742 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -482,6 +482,12 @@ static int x25_listen(struct socket *sock, int backlog)
 	int rc = -EOPNOTSUPP;
 
 	lock_sock(sk);
+	if (sock->state != SS_UNCONNECTED) {
+		rc = -EINVAL;
+		release_sock(sk);
+		return rc;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&x25_sk(sk)->dest_addr, 0, X25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
-- 
2.25.1

Re: [PATCH v3] net/x25: Fix to not accept on connected socket

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller <davem@davemloft.net>:

On Wed, 25 Jan 2023 03:05:14 -0800 you wrote:
> If you call listen() and accept() on an already connect()ed
> x25 socket, accept() can successfully connect.
> This is because when the peer socket sends data to sendmsg,
> the skb with its own sk stored in the connected socket's
> sk->sk_receive_queue is connected, and x25_accept() dequeues
> the skb waiting in the sk->sk_receive_queue.
> 
> [...]

Here is the summary with links:
  - [v3] net/x25: Fix to not accept on connected socket
    https://git.kernel.org/netdev/net-next/c/f2b0b5210f67

You are awesome, thank you!
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