net/ipv6: Change address check to always take a device argument

ipv6_chk_addr_and_flags determines if an address is a local address and
optionally if it is an address on a specific device. For example, it is
called by ip6_route_info_create to determine if a given gateway address
is a local address. The address check currently does not consider L3
domains and as a result does not allow a route to be added in one VRF
if the nexthop points to an address in a second VRF. e.g.,

    $ ip route add 2001:db8:1::/64 vrf r2 via 2001:db8:102::23
    Error: Invalid gateway address.

where 2001:db8:102::23 is an address on an interface in vrf r1.

ipv6_chk_addr_and_flags needs to allow callers to always pass in a device
with a separate argument to not limit the address to the specific device.
The device is used used to determine the L3 domain of interest.

To that end add an argument to skip the device check and update callers
to always pass a device where possible and use the new argument to mean
any address in the domain.

Update a handful of users of ipv6_chk_addr with a NULL dev argument. This
patch handles the change to these callers without adding the domain check.

ip6_validate_gw needs to handle 2 cases - one where the device is given
as part of the nexthop spec and the other where the device is resolved.
There is at least 1 VRF case where deferring the check to only after
the route lookup has resolved the device fails with an unintuitive error
"RTNETLINK answers: No route to host" as opposed to the preferred
"Error: Gateway can not be a local address." The 'no route to host'
error is because of the fallback to a full lookup. The check is done
twice to avoid this error.

Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 4 deletions

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 23ced851fdb1..939d122e71b4 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2632,7 +2632,9 @@ static int ip6_validate_gw(struct net *net, struct fib6_config *cfg,
 {
 	const struct in6_addr *gw_addr = &cfg->fc_gateway;
 	int gwa_type = ipv6_addr_type(gw_addr);
+	bool skip_dev = gwa_type & IPV6_ADDR_LINKLOCAL ? false : true;
 	const struct net_device *dev = *_dev;
+	bool need_addr_check = !dev;
 	int err = -EINVAL;
 
 	/* if gw_addr is local we will fail to detect this in case
@@ -2640,10 +2642,9 @@ static int ip6_validate_gw(struct net *net, struct fib6_config *cfg,
 	 * will return already-added prefix route via interface that
 	 * prefix route was assigned to, which might be non-loopback.
 	 */
-	if (ipv6_chk_addr_and_flags(net, gw_addr,
-				    gwa_type & IPV6_ADDR_LINKLOCAL ?
-				    dev : NULL, 0, 0)) {
-		NL_SET_ERR_MSG(extack, "Invalid gateway address");
+	if (dev &&
+	    ipv6_chk_addr_and_flags(net, gw_addr, dev, skip_dev, 0, 0)) {
+		NL_SET_ERR_MSG(extack, "Gateway can not be a local address");
 		goto out;
 	}
 
@@ -2683,6 +2684,16 @@ static int ip6_validate_gw(struct net *net, struct fib6_config *cfg,
 			       "Egress device can not be loopback device for this route");
 		goto out;
 	}
+
+	/* if we did not check gw_addr above, do so now that the
+	 * egress device has been resolved.
+	 */
+	if (need_addr_check &&
+	    ipv6_chk_addr_and_flags(net, gw_addr, dev, skip_dev, 0, 0)) {
+		NL_SET_ERR_MSG(extack, "Gateway can not be a local address");
+		goto out;
+	}
+
 	err = 0;
 out:
 	return err;