Subject: Re: [PATCH net-next] sockopt: Make SO_BINDTODEVICE readable

From: Brian Haley <[email-masked]>
Date: Mon, 22 Oct 2012 14:04:45 -0400

On 10/19/2012 05:55 AM, Pavel Emelyanov wrote:
> The SO_BINDTODEVICE option is the only SOL_SOCKET one that can be set, but
> cannot be get via sockopt API. The only way we can find the device id a
> socket is bound to is via sock-diag interface. But the diag works only on
> hashed sockets, while the opt in question can be set for yet unhashed one.
> 
> That said, in order to know what device a socket is bound to (we do want
> to know this in checkpoint-restore project) I propose to make this option
> getsockopt-able and report the respective device index.
> 
> Another solution to the problem might be to teach the sock-diag reporting
> info on unhashed sockets. Should I go this way instead?
> 
> Signed-off-by: Pavel Emelyanov <[email-masked]>
> 
> ---
> 
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 8a146cf..c49412c 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1074,6 +1074,9 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
>  	case SO_NOFCS:
>  		v.val = sock_flag(sk, SOCK_NOFCS);
>  		break;
> +	case SO_BINDTODEVICE:
> +		v.val = sk->sk_bound_dev_if;
> +		break;
>  	default:
>  		return -ENOPROTOOPT;
>  	}

Doesn't this make the set and get non-symmetrical?  For example, setsockopt()
would take "eth0", but getsockopt() would return 2.  The following patch would
return a string, or -ENODEV if not set.

-Brian

---

Change getsockopt(SO_BINDTODEVICE) to be symmetrical with setsockopt() by
returning the interface name as a string.

Signed-off-by: Brian Haley <[email-masked]>

diff --git a/net/core/sock.c b/net/core/sock.c
index c49412c..69b9d92 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -505,7 +505,8 @@ struct dst_entry *sk_dst_check(struct sock *sk, u32 cookie)
 }
 EXPORT_SYMBOL(sk_dst_check);

-static int sock_bindtodevice(struct sock *sk, char __user *optval, int optlen)
+static int sock_setbindtodevice(struct sock *sk, char __user *optval,
+				int optlen)
 {
 	int ret = -ENOPROTOOPT;
 #ifdef CONFIG_NETDEVICES
@@ -562,6 +563,49 @@ out:
 	return ret;
 }

+static int sock_getbindtodevice(struct sock *sk, char __user *optval,
+				int __user *optlen, int len)
+{
+	int ret = -ENOPROTOOPT;
+#ifdef CONFIG_NETDEVICES
+	struct net *net = sock_net(sk);
+	struct net_device *dev;
+	char devname[IFNAMSIZ];
+
+	ret = 0;
+	if (sk->sk_bound_dev_if == 0)
+		goto out;
+
+	ret = -EINVAL;
+	if (len < IFNAMSIZ)
+		goto out;
+	if (len > IFNAMSIZ)
+		len = IFNAMSIZ;
+
+	rcu_read_lock();
+	dev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if);
+	if (dev)
+		strcpy(dev->name, devname);
+	rcu_read_unlock();
+	ret = -ENODEV;
+	if (!dev)
+		goto out;
+
+	ret = -EFAULT;
+	if (copy_to_user(optval, devname, len))
+		goto out;
+
+	if (put_user(len, optlen))
+		goto out;
+
+	ret = 0;
+
+out:
+#endif
+
+	return ret;
+}
+
 static inline void sock_valbool_flag(struct sock *sk, int bit, int valbool)
 {
 	if (valbool)
@@ -589,7 +633,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 	 */

 	if (optname == SO_BINDTODEVICE)
-		return sock_bindtodevice(sk, optval, optlen);
+		return sock_setbindtodevice(sk, optval, optlen);

 	if (optlen < sizeof(int))
 		return -EINVAL;
@@ -1074,9 +1118,10 @@ int sock_getsockopt(struct socket *sock, int level, int
optname,
 	case SO_NOFCS:
 		v.val = sock_flag(sk, SOCK_NOFCS);
 		break;
+
 	case SO_BINDTODEVICE:
-		v.val = sk->sk_bound_dev_if;
-		break;
+		return sock_getbindtodevice(sk, optval, optlen, len);
+
 	default:
 		return -ENOPROTOOPT;
 	}