[PATCH net-next] Extending bpf_setsockopt with SO_BINDTODEVICE sockopt

[Ferenc Fejes <fejes@xxxxxxxxxxx>]

This option makes possible to programatically bind sockets to netdevices.
With the help of this option sockets of VRF unaware applications
could be distributed between multiple VRFs with eBPF sock_ops program.
This let the applications benefit from the multiple possible routes.

Signed-off-by: Ferenc Fejes <fejes@xxxxxxxxxxx>
---
 net/core/filter.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 822d662f97ef..25dac75bfc5d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4248,6 +4248,9 @@ static const struct bpf_func_proto bpf_get_socket_uid_proto = {
 static int _bpf_setsockopt(struct sock *sk, int level, int optname,
 			   char *optval, int optlen, u32 flags)
 {
+	char devname[IFNAMSIZ];
+	struct net *net;
+	int ifindex;
 	int ret = 0;
 	int val;
 
@@ -4257,7 +4260,7 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
 	sock_owned_by_me(sk);
 
 	if (level == SOL_SOCKET) {
-		if (optlen != sizeof(int))
+		if (optlen != sizeof(int) && optname != SO_BINDTODEVICE)
 			return -EINVAL;
 		val = *((int *)optval);
 
@@ -4298,6 +4301,40 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
 				sk_dst_reset(sk);
 			}
 			break;
+		case SO_BINDTODEVICE:
+			ret = -ENOPROTOOPT;
+#ifdef CONFIG_NETDEVICES
+			net = sock_net(sk);
+			strncpy(devname, optval,
+				min_t(long, optlen, IFNAMSIZ-1));
+			devname[IFNAMSIZ-1] = 0;
+			ifindex = 0;
+			if (devname[0] != '\0') {
+				struct net_device *dev;
+
+				rcu_read_lock();
+				dev = dev_get_by_name_rcu(net, devname);
+				if (dev)
+					ifindex = dev->ifindex;
+				rcu_read_unlock();
+				ret = -ENODEV;
+				if (!dev)
+					break;
+			}
+			ret = -EPERM;
+			if (sk->sk_bound_dev_if &&
+				!ns_capable(net->user_ns, CAP_NET_RAW))
+				break;
+			ret = -EINVAL;
+			if (ifindex < 0)
+				break;
+			sk->sk_bound_dev_if = ifindex;
+			if (sk->sk_prot->rehash)
+				sk->sk_prot->rehash(sk);
+			sk_dst_reset(sk);
+			ret = 0;
+#endif
+			break;
 		default:
 			ret = -EINVAL;
 		}
-- 
2.17.1