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

From: Pavel Emelyanov <[email-masked]>
Date: Tue, 23 Oct 2012 00:28:33 +0400

On 10/22/2012 10:04 PM, Brian Haley wrote:
> 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.

It will, but since device name and index are two equal device "IDs" I assumed
it would be OK.

However, some comments inline.

> 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;

It will return 0 if device is not set, thus making it impossible to detect
this situation.

> +	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;

What's the point in reporting IFNAMSIZ to the userspace always, taking
into account that this constant is exported there anyway?

> +	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;
>  	}
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to [email-masked]
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> .
>