[PATCH net v2 2/4] ipv6: fix source address selection with route leak

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

By default, an address assigned to the output interface is selected when
the source address is not specified. This is problematic when a route,
configured in a vrf, uses an interface from another vrf (aka route leak).
The original vrf does not own the selected source address.

Let's add a check against the output interface and call the appropriate
function to select the source address.

CC: stable@vger.kernel.org
Fixes: 0d240e7811c4 ("net: vrf: Implement get_saddr for IPv6")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 include/net/ip6_route.h | 19 ++++++++++++-------
 net/ipv6/ip6_output.c   |  1 +
 net/ipv6/route.c        |  2 +-
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index a18ed24fed94..a7c27f0c6bce 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -127,18 +127,23 @@ void rt6_age_exceptions(struct fib6_info *f6i, struct fib6_gc_args *gc_args,
 
 static inline int ip6_route_get_saddr(struct net *net, struct fib6_info *f6i,
 				      const struct in6_addr *daddr,
-				      unsigned int prefs,
+				      unsigned int prefs, int l3mdev_index,
 				      struct in6_addr *saddr)
 {
+	struct net_device *l3mdev;
+	struct net_device *dev;
+	bool same_vrf;
 	int err = 0;
 
-	if (f6i && f6i->fib6_prefsrc.plen) {
+	rcu_read_lock();
+	l3mdev = dev_get_by_index_rcu(net, l3mdev_index);
+	dev = f6i ? fib6_info_nh_dev(f6i) : NULL;
+	same_vrf = l3mdev == NULL || l3mdev_master_dev_rcu(dev) == l3mdev;
+	if (f6i && f6i->fib6_prefsrc.plen && same_vrf)
 		*saddr = f6i->fib6_prefsrc.addr;
-	} else {
-		struct net_device *dev = f6i ? fib6_info_nh_dev(f6i) : NULL;
-
-		err = ipv6_dev_get_saddr(net, dev, daddr, prefs, saddr);
-	}
+	else
+		err = ipv6_dev_get_saddr(net, same_vrf ? dev : l3mdev, daddr, prefs, saddr);
+	rcu_read_unlock();
 
 	return err;
 }
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 27d8725445e3..784424ac4147 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1124,6 +1124,7 @@ static int ip6_dst_lookup_tail(struct net *net, const struct sock *sk,
 		from = rt ? rcu_dereference(rt->from) : NULL;
 		err = ip6_route_get_saddr(net, from, &fl6->daddr,
 					  sk ? READ_ONCE(inet6_sk(sk)->srcprefs) : 0,
+					  fl6->flowi6_l3mdev,
 					  &fl6->saddr);
 		rcu_read_unlock();
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 8d72ca0b086d..c9a9506b714d 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5689,7 +5689,7 @@ static int rt6_fill_node(struct net *net, struct sk_buff *skb,
 				goto nla_put_failure;
 	} else if (dest) {
 		struct in6_addr saddr_buf;
-		if (ip6_route_get_saddr(net, rt, dest, 0, &saddr_buf) == 0 &&
+		if (ip6_route_get_saddr(net, rt, dest, 0, 0, &saddr_buf) == 0 &&
 		    nla_put_in6_addr(skb, RTA_PREFSRC, &saddr_buf))
 			goto nla_put_failure;
 	}
-- 
2.43.1