net: Propagate lookup failure in l3mdev_get_saddr to caller

Commands run in a vrf context are not failing as expected on a route lookup:
    root@kenny:~# ip ro ls table vrf-red
    unreachable default

    root@kenny:~# ping -I vrf-red -c1 -w1 10.100.1.254
    ping: Warning: source address might be selected on device other than vrf-red.
    PING 10.100.1.254 (10.100.1.254) from 0.0.0.0 vrf-red: 56(84) bytes of data.

    --- 10.100.1.254 ping statistics ---
    2 packets transmitted, 0 received, 100% packet loss, time 999ms

Since the vrf table does not have a route for 10.100.1.254 the ping
should have failed. The saddr lookup causes a full VRF table lookup.
Propogating a lookup failure to the user allows the command to fail as
expected:

    root@kenny:~# ping -I vrf-red -c1 -w1 10.100.1.254
    connect: No route to host

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 33 insertions, 14 deletions

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 4f9748457f5a..0a242b200df4 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -800,7 +800,7 @@ static struct rtable *vrf_get_rtable(const struct net_device *dev,
 }
 
 /* called under rcu_read_lock */
-static void vrf_get_saddr(struct net_device *dev, struct flowi4 *fl4)
+static int vrf_get_saddr(struct net_device *dev, struct flowi4 *fl4)
 {
         struct fib_result res = { .tclassid = 0 };
         struct net *net = dev_net(dev);
@@ -808,9 +808,10 @@ static void vrf_get_saddr(struct net_device *dev, struct flowi4 *fl4)
         u8 flags = fl4->flowi4_flags;
         u8 scope = fl4->flowi4_scope;
         u8 tos = RT_FL_TOS(fl4);
+        int rc;
 
         if (unlikely(!fl4->daddr))
-                return;
+                return 0;
 
         fl4->flowi4_flags |= FLOWI_FLAG_SKIP_NH_OIF;
         fl4->flowi4_iif = LOOPBACK_IFINDEX;
@@ -818,7 +819,8 @@ static void vrf_get_saddr(struct net_device *dev, struct flowi4 *fl4)
         fl4->flowi4_scope = ((tos & RTO_ONLINK) ?
                              RT_SCOPE_LINK : RT_SCOPE_UNIVERSE);
 
-        if (!fib_lookup(net, fl4, &res, 0)) {
+        rc = fib_lookup(net, fl4, &res, 0);
+        if (!rc) {
                 if (res.type == RTN_LOCAL)
                         fl4->saddr = res.fi->fib_prefsrc ? : fl4->daddr;
                 else
@@ -828,6 +830,8 @@ static void vrf_get_saddr(struct net_device *dev, struct flowi4 *fl4)
         fl4->flowi4_flags = flags;
         fl4->flowi4_tos = orig_tos;
         fl4->flowi4_scope = scope;
+
+        return rc;
 }
 
 #if IS_ENABLED(CONFIG_IPV6)
diff --git a/include/net/l3mdev.h b/include/net/l3mdev.h
index 774d85b2d5d9..5689a0c749f7 100644
--- a/include/net/l3mdev.h
+++ b/include/net/l3mdev.h
@@ -29,7 +29,7 @@ struct l3mdev_ops {
         /* IPv4 ops */
         struct rtable * (*l3mdev_get_rtable)(const struct net_device *dev,
                                              const struct flowi4 *fl4);
-        void            (*l3mdev_get_saddr)(struct net_device *dev,
+        int             (*l3mdev_get_saddr)(struct net_device *dev,
                                             struct flowi4 *fl4);
 
         /* IPv6 ops */
@@ -112,10 +112,11 @@ static inline bool netif_index_is_l3_master(struct net *net, int ifindex)
         return rc;
 }
 
-static inline void l3mdev_get_saddr(struct net *net, int ifindex,
-                                    struct flowi4 *fl4)
+static inline int l3mdev_get_saddr(struct net *net, int ifindex,
+                                   struct flowi4 *fl4)
 {
         struct net_device *dev;
+        int rc = 0;
 
         if (ifindex) {
 
@@ -124,11 +125,13 @@ static inline void l3mdev_get_saddr(struct net *net, int ifindex,
                 dev = dev_get_by_index_rcu(net, ifindex);
                 if (dev && netif_is_l3_master(dev) &&
                     dev->l3mdev_ops->l3mdev_get_saddr) {
-                        dev->l3mdev_ops->l3mdev_get_saddr(dev, fl4);
+                        rc = dev->l3mdev_ops->l3mdev_get_saddr(dev, fl4);
                 }
 
                 rcu_read_unlock();
         }
+
+        return rc;
 }
 
 static inline struct dst_entry *l3mdev_get_rt6_dst(const struct net_device *dev,
@@ -200,9 +203,10 @@ static inline bool netif_index_is_l3_master(struct net *net, int ifindex)
         return false;
 }
 
-static inline void l3mdev_get_saddr(struct net *net, int ifindex,
-                                    struct flowi4 *fl4)
+static inline int l3mdev_get_saddr(struct net *net, int ifindex,
+                                   struct flowi4 *fl4)
 {
+        return 0;
 }
 
 static inline
diff --git a/include/net/route.h b/include/net/route.h
index ee81307863d5..a3b9ef74a389 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -283,7 +283,12 @@ static inline struct rtable *ip_route_connect(struct flowi4 *fl4,
                               sport, dport, sk);
 
         if (!src && oif) {
-                l3mdev_get_saddr(net, oif, fl4);
+                int rc;
+
+                rc = l3mdev_get_saddr(net, oif, fl4);
+                if (rc < 0)
+                        return ERR_PTR(rc);
+
                 src = fl4->saddr;
         }
         if (!dst || !src) {
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 63e5be0abd86..bc35f1842512 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -601,8 +601,11 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
                             (inet->hdrincl ? FLOWI_FLAG_KNOWN_NH : 0),
                            daddr, saddr, 0, 0);
 
-        if (!saddr && ipc.oif)
-                l3mdev_get_saddr(net, ipc.oif, &fl4);
+        if (!saddr && ipc.oif) {
+                err = l3mdev_get_saddr(net, ipc.oif, &fl4);
+                if (err < 0)
+                        goto done;
+        }
 
         if (!inet->hdrincl) {
                 rfv.msg = msg;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 0c7b0e61b917..c43890848641 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1025,8 +1025,11 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
                                    flow_flags,
                                    faddr, saddr, dport, inet->inet_sport);
 
-                if (!saddr && ipc.oif)
-                        l3mdev_get_saddr(net, ipc.oif, fl4);
+                if (!saddr && ipc.oif) {
+                        err = l3mdev_get_saddr(net, ipc.oif, fl4);
+                        if (err < 0)
+                                goto out;
+                }
 
                 security_sk_classify_flow(sk, flowi4_to_flowi(fl4));
                 rt = ip_route_output_flow(net, fl4, sk);