lib: fix binding to a vrf

There are two possible use-cases for the `vrf_bind` function:
- bind socket to an interface in a vrf
- bind socket to a vrf device

For the former case, there's one problem - success is returned when the
interface is not found. In that case, the socket is left unbound without
throwing an error.

For the latter case, there are multiple possible problems:
- If the name is not set, then the socket is left unbound (zebra, vrrp).
- If the name is "default" and there's an interface with that name in the
  default VRF, then the socket is bound to that interface.
- In most daemons, if the router is configured before the VRF is actually
  created, we're trying to open and bind the socket right after the
  daemon receives a VRF registration from zebra. We may not receive the
  VRF-interface registration from zebra yet at that point. Therefore,
  `if_lookup_by_name` fails, and the socket is left unbound.

This commit fixes all the issues and updates the function description.

Suggested-by: Pat Ruddy <pat@voltanet.io>
Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>

1 files changed, 38 insertions, 13 deletions

diff --git a/lib/vrf.c b/lib/vrf.c
index d99ec12ba..185a11664 100644
--- a/lib/vrf.c
+++ b/lib/vrf.c
@@ -994,25 +994,50 @@ const char *vrf_get_default_name(void)
 	return vrf_default_name;
 }
 
-int vrf_bind(vrf_id_t vrf_id, int fd, const char *name)
+int vrf_bind(vrf_id_t vrf_id, int fd, const char *ifname)
 {
 	int ret = 0;
 	struct interface *ifp;
+	struct vrf *vrf;
+
+	if (fd < 0)
+		return -1;
+
+	if (vrf_id == VRF_UNKNOWN)
+		return -1;
+
+	/* can't bind to a VRF that doesn't exist */
+	vrf = vrf_lookup_by_id(vrf_id);
+	if (!vrf_is_enabled(vrf))
+		return -1;
+
+	if (ifname && strcmp(ifname, vrf->name)) {
+		/* binding to a regular interface */
+
+		/* can't bind to an interface that doesn't exist */
+		ifp = if_lookup_by_name(ifname, vrf_id);
+		if (!ifp)
+			return -1;
+	} else {
+		/* binding to a VRF device */
+
+		/* nothing to do for netns */
+		if (vrf_is_backend_netns())
+			return 0;
+
+		/* nothing to do for default vrf */
+		if (vrf_id == VRF_DEFAULT)
+			return 0;
+
+		ifname = vrf->name;
+	}
 
-	if (fd < 0 || name == NULL)
-		return fd;
-	/* the device should exist
-	 * otherwise we should return
-	 * case ifname = vrf in netns mode => return
-	 */
-	ifp = if_lookup_by_name(name, vrf_id);
-	if (!ifp)
-		return fd;
 #ifdef SO_BINDTODEVICE
-	ret = setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, name, strlen(name)+1);
+	ret = setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, ifname,
+			 strlen(ifname) + 1);
 	if (ret < 0)
-		zlog_debug("bind to interface %s failed, errno=%d", name,
-			   errno);
+		zlog_err("bind to interface %s failed, errno=%d", ifname,
+			 errno);
 #endif /* SO_BINDTODEVICE */
 	return ret;
 }