[PATCH] net: change recvform to return same address length as getsockname on unnamed unix sockets

[PATCH] net: change recvform to return same address length as getsockname on unnamed unix sockets

[Pavel Pergamenshchik]

unix_*_recvmsg() returns zero-length sockaddr if the sender is an
unnamed AF_UNIX socket. Change it to return a two-byte sockaddr with
just the address family, to be consistent with unix_getname().

Signed-off-by: Pavel Pergamenshchik <ppergame@gmail.com>

---
Minimal example at http://xzrq.net/uaddrwtf.c
Solaris/OS X print 16 and 16. Linux prints 0 and 2 as described above.

--- a/net/unix/af_unix.c	2010-04-01 16:02:33.000000000 -0700
+++ b/net/unix/af_unix.c	2010-04-21 20:17:43.564703748 -0700
@@ -1634,9 +1634,13 @@
 static void unix_copy_addr(struct msghdr *msg, struct sock *sk)
 {
 	struct unix_sock *u = unix_sk(sk);
+	struct sockaddr_un *sunaddr;

-	msg->msg_namelen = 0;
-	if (u->addr) {
+	if (!u->addr) {
+		msg->msg_namelen = sizeof(short);
+		sunaddr = msg->msg_name;
+		sunaddr->sun_family = AF_UNIX;
+	} else {
 		msg->msg_namelen = u->addr->len;
 		memcpy(msg->msg_name, u->addr->name, u->addr->len);
 	}

Re: [PATCH] net: change recvform to return same address length as getsockname on unnamed unix sockets

[David Miller]

From: Pavel Pergamenshchik <ppergame@gmail.com>
Date: Wed, 21 Apr 2010 20:29:25 -0700

> unix_*_recvmsg() returns zero-length sockaddr if the sender is an
> unnamed AF_UNIX socket. Change it to return a two-byte sockaddr with
> just the address family, to be consistent with unix_getname().
> 
> Signed-off-by: Pavel Pergamenshchik <ppergame@gmail.com>

Since we've behaved this way for at least 10 years, the existing
behavior is the user visible ABI and the risk of breaking things by
making the change is too great.

I'm not applying this, sorry.