netdev - [PATCH net-next] Extending bpf_setsockopt with SO

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Message-Id: <20200521125247.30178-1-fejes@inf.elte.hu>
Date:   Thu, 21 May 2020 14:52:47 +0200
From:   Ferenc Fejes <fejes@....elte.hu>
To:     netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Lawrence Brakmo <brakmo@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Ferenc Fejes <fejes@....elte.hu>
Subject: [PATCH net-next] Extending bpf_setsockopt with SO_BINDTODEVICE sockopt

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@....elte.hu>
---
 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