netdev - Re: EINVAL when using connect() for udp sockets

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Date:   Tue, 28 Mar 2017 17:52:36 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Daurnimator <quae@...rnimator.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        William Ahern <william@...handclement.com>,
        "Santi T." <santitm99@...il.com>,
        Michael Kerrisk-manpages <mtk.manpages@...il.com>
Subject: Re: EINVAL when using connect() for udp sockets

On Tue, 2017-03-28 at 16:11 -0700, Eric Dumazet wrote:

> Yes, this looks better.
> 
> Although you probably need to change a bit later this part :
> 
> if (!inet->inet_saddr)
> 	inet->inet_saddr = fl4->saddr;  /* Update source address */
> 

I came up with the following tested patch for IPv4

diff --git a/net/ipv4/datagram.c b/net/ipv4/datagram.c
index f915abff1350a86af8d5bb89725b751c061b0fb5..1454b6191e0d38ffae0ae260578858285bc5f77b 100644
--- a/net/ipv4/datagram.c
+++ b/net/ipv4/datagram.c
@@ -40,7 +40,7 @@ int __ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
 	sk_dst_reset(sk);
 
 	oif = sk->sk_bound_dev_if;
-	saddr = inet->inet_saddr;
+	saddr = (sk->sk_userlocks & SOCK_BINDADDR_LOCK) ? inet->inet_saddr : 0;
 	if (ipv4_is_multicast(usin->sin_addr.s_addr)) {
 		if (!oif)
 			oif = inet->mc_index;
@@ -64,9 +64,8 @@ int __ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
 		err = -EACCES;
 		goto out;
 	}
-	if (!inet->inet_saddr)
+	if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK)) {
 		inet->inet_saddr = fl4->saddr;	/* Update source address */
-	if (!inet->inet_rcv_saddr) {
 		inet->inet_rcv_saddr = fl4->saddr;
 		if (sk->sk_prot->rehash)
 			sk->sk_prot->rehash(sk);