Re: [PATCH] af_unix: Only allow recv on connected seqpacket sockets.

[David Miller <davem@davemloft.net>]

From: ebiederm@xmission.com (Eric W. Biederman)
Date: Sun, 24 Apr 2011 04:54:57 -0700

> +static int unix_seqpacket_recvmsg(struct kiocb *iocb, struct socket *sock,
> +			      struct msghdr *msg, size_t size,
> +			      int flags)
> +{
> +	struct sock *sk = sock->sk;
> +
> +	if (sk->sk_state != TCP_ESTABLISHED)
> +		return -ENOTCONN;

As for unix_seqpacket_sendmsg(), you need to add a check for sock_error()
or similar here otherwise -ECONNRESET is not reported correctly.

In fact, recvmsg() is even harder than sendmsg() to handle correctly,
because we have to also properly report EOF on seqpacket sockets which
have RCV_SHUTDOWN set.

So a lot more work has to go into this change to make it fix the bug
without also breaking existing semantics.

Anyways, see:

commit 6e14891f4d16f8a9e0bc3a8408f73b3aed93ab0a
Author: James Morris <jmorris@redhat.com>
Date:   Fri Nov 19 07:02:41 2004 -0800

    [AF_UNIX]: Don't lose ECONNRESET in unix_seqpacket_sendmsg()
    
    The fix for SELinux w/SOCK_SEQPACKET had an error,
    noted by Alan Cox.  This fixes it.
    
    Signed-off-by: James Morris <jmorris@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 16faa9d..8902c4a 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1513,13 +1513,18 @@ out_err:
 static int unix_seqpacket_sendmsg(struct kiocb *kiocb, struct socket *sock,
 				  struct msghdr *msg, size_t len)
 {
+	int err;
 	struct sock *sk = sock->sk;
 	
+	err = sock_error(sk);
+	if (err)
+		return err;
+
 	if (sk->sk_state != TCP_ESTABLISHED)
 		return -ENOTCONN;
 
-	if (msg->msg_name || msg->msg_namelen)
-		return -EINVAL;
+	if (msg->msg_namelen)
+		msg->msg_namelen = 0;
 
 	return unix_dgram_sendmsg(kiocb, sock, msg, len);
 }