local-addresses: honor RTA_PREFSRC field of gateway

Fixes #34739.

diff --git a/src/shared/local-addresses.c b/src/shared/local-addresses.c
index 2f9e75789b5aa5a7262ac3b6bb0d7c4a78321b4b..4e811ba2bf6cb564fbeae45fc4fe58c192365828 100644 (file)
--- a/src/shared/local-addresses.c
+++ b/src/shared/local-addresses.c
@@ -81,7 +81,8 @@ static int add_local_address_full(
                 uint32_t priority,
                 uint32_t weight,
                 int family,
-                const union in_addr_union *address) {
+                const union in_addr_union *address,
+                const union in_addr_union *prefsrc) {
 
         assert(list);
         assert(n_list);
@@ -99,6 +100,7 @@ static int add_local_address_full(
                 .weight = weight,
                 .family = family,
                 .address = *address,
+                .prefsrc = prefsrc ? *prefsrc : IN_ADDR_NULL,
         };
 
         return 1;
@@ -112,7 +114,10 @@ int add_local_address(
                 int family,
                 const union in_addr_union *address) {
 
-        return add_local_address_full(list, n_list, ifindex, scope, 0, 0, family, address);
+        return add_local_address_full(
+                        list, n_list, ifindex,
+                        scope, /* priority = */ 0, /* weight = */ 0,
+                        family, address, /* prefsrc = */ NULL);
 }
 
 int local_addresses(
@@ -235,9 +240,14 @@ static int add_local_gateway(
                 uint32_t priority,
                 uint32_t weight,
                 int family,
-                const union in_addr_union *address) {
-
-        return add_local_address_full(list, n_list, ifindex, 0, priority, weight, family, address);
+                const union in_addr_union *address,
+                const union in_addr_union *prefsrc) {
+
+        return add_local_address_full(
+                        list, n_list,
+                        ifindex,
+                        /* scope = */ 0, priority, weight,
+                        family, address, prefsrc);
 }
 
 static int parse_nexthop_one(
@@ -246,6 +256,7 @@ static int parse_nexthop_one(
                 bool allow_via,
                 int family,
                 uint32_t priority,
+                const union in_addr_union *prefsrc,
                 const struct rtnexthop *rtnh) {
 
         bool has_gw = false;
@@ -268,7 +279,7 @@ static int parse_nexthop_one(
 
                         union in_addr_union a;
                         memcpy(&a, RTA_DATA(attr), FAMILY_ADDRESS_SIZE(family));
-                        r = add_local_gateway(list, n_list, rtnh->rtnh_ifindex, priority, rtnh->rtnh_hops, family, &a);
+                        r = add_local_gateway(list, n_list, rtnh->rtnh_ifindex, priority, rtnh->rtnh_hops, family, &a, prefsrc);
                         if (r < 0)
                                 return r;
 
@@ -294,7 +305,8 @@ static int parse_nexthop_one(
                                 return -EBADMSG; /* gateway address should be always IPv6. */
 
                         r = add_local_gateway(list, n_list, rtnh->rtnh_ifindex, priority, rtnh->rtnh_hops, via->family,
-                                              &(union in_addr_union) { .in6 = via->address.in6 });
+                                              &(union in_addr_union) { .in6 = via->address.in6 },
+                                              /* prefsrc = */ NULL);
                         if (r < 0)
                                 return r;
 
@@ -311,6 +323,7 @@ static int parse_nexthops(
                 bool allow_via,
                 int family,
                 uint32_t priority,
+                const union in_addr_union *prefsrc,
                 const struct rtnexthop *rtnh,
                 size_t size) {
 
@@ -334,7 +347,7 @@ static int parse_nexthops(
                 if (ifindex > 0 && rtnh->rtnh_ifindex != ifindex)
                         goto next_nexthop;
 
-                r = parse_nexthop_one(list, n_list, allow_via, family, priority, rtnh);
+                r = parse_nexthop_one(list, n_list, allow_via, family, priority, prefsrc, rtnh);
                 if (r < 0)
                         return r;
 
@@ -393,6 +406,7 @@ int local_gateways(
                 return r;
 
         for (sd_netlink_message *m = reply; m; m = sd_netlink_message_next(m)) {
+                union in_addr_union prefsrc = IN_ADDR_NULL;
                 uint16_t type;
                 unsigned char dst_len, src_len, table;
                 uint32_t ifi = 0, priority = 0;
@@ -439,6 +453,10 @@ int local_gateways(
                 if (af != AF_UNSPEC && af != family)
                         continue;
 
+                r = netlink_message_read_in_addr_union(m, RTA_PREFSRC, family, &prefsrc);
+                if (r < 0 && r != -ENODATA)
+                        return r;
+
                 r = sd_netlink_message_read_u32(m, RTA_OIF, &ifi);
                 if (r < 0 && r != -ENODATA)
                         return r;
@@ -453,7 +471,7 @@ int local_gateways(
                         if (r < 0 && r != -ENODATA)
                                 return r;
                         if (r >= 0) {
-                                r = add_local_gateway(&list, &n_list, ifi, priority, 0, family, &gateway);
+                                r = add_local_gateway(&list, &n_list, ifi, priority, 0, family, &gateway, &prefsrc);
                                 if (r < 0)
                                         return r;
 
@@ -474,8 +492,10 @@ int local_gateways(
                                 if (via.family != AF_INET6)
                                         return -EBADMSG;
 
+                                /* Ignore prefsrc, and let's take the source address by socket command, if necessary. */
                                 r = add_local_gateway(&list, &n_list, ifi, priority, 0, via.family,
-                                                      &(union in_addr_union) { .in6 = via.address.in6 });
+                                                      &(union in_addr_union) { .in6 = via.address.in6 },
+                                                      /* prefsrc = */ NULL);
                                 if (r < 0)
                                         return r;
                         }
@@ -490,7 +510,7 @@ int local_gateways(
                 if (r < 0 && r != -ENODATA)
                         return r;
                 if (r >= 0) {
-                        r = parse_nexthops(&list, &n_list, ifindex, allow_via, family, priority, rta_multipath, rta_len);
+                        r = parse_nexthops(&list, &n_list, ifindex, allow_via, family, priority, &prefsrc, rta_multipath, rta_len);
                         if (r < 0)
                                 return r;
                 }
@@ -512,7 +532,51 @@ static int add_local_outbound(
                 int family,
                 const union in_addr_union *address) {
 
-        return add_local_address_full(list, n_list, ifindex, 0, 0, 0, family, address);
+        return add_local_address_full(
+                        list, n_list, ifindex,
+                        /* scope = */ 0, /* priority = */ 0, /* weight = */ 0,
+                        family, address, /* prefsrc = */ NULL);
+}
+
+static int add_local_outbound_by_prefsrc(
+                struct local_address **list,
+                size_t *n_list,
+                const struct local_address *gateway,
+                const struct local_address *addresses,
+                size_t n_addresses) {
+
+        int r;
+
+        assert(list);
+        assert(n_list);
+        assert(gateway);
+
+        if (!in_addr_is_set(gateway->family, &gateway->prefsrc))
+                return 0;
+
+        /* If the gateway has prefsrc, then let's honor the field. But, check if the address is assigned to
+         * the same interface, like we do with SO_BINDTOINDEX. */
+
+        bool found = false;
+        FOREACH_ARRAY(a, addresses, n_addresses) {
+                if (a->ifindex != gateway->ifindex)
+                        continue;
+                if (a->family != gateway->family)
+                        continue;
+                if (in_addr_equal(a->family, &a->address, &gateway->prefsrc) <= 0)
+                        continue;
+
+                found = true;
+                break;
+        }
+        if (!found)
+                return -EHOSTUNREACH;
+
+        r = add_local_outbound(list, n_list, gateway->ifindex, gateway->family, &gateway->prefsrc);
+        if (r < 0)
+                return r;
+
+        return 1;
 }
 
 int local_outbounds(
@@ -521,9 +585,9 @@ int local_outbounds(
                 int af,
                 struct local_address **ret) {
 
-        _cleanup_free_ struct local_address *list = NULL, *gateways = NULL;
+        _cleanup_free_ struct local_address *list = NULL, *gateways = NULL, *addresses = NULL;
         size_t n_list = 0;
-        int r, n_gateways;
+        int r, n_gateways, n_addresses;
 
         /* Determines our default outbound addresses, i.e. the "primary" local addresses we use to talk to IP
          * addresses behind the default routes. This is still an address of the local host (i.e. this doesn't
@@ -544,11 +608,21 @@ int local_outbounds(
                 return 0;
         }
 
+        n_addresses = local_addresses(context, ifindex, af, &addresses);
+        if (n_addresses < 0)
+                return n_addresses;
+
         FOREACH_ARRAY(i, gateways, n_gateways) {
                 _cleanup_close_ int fd = -EBADF;
                 union sockaddr_union sa;
                 socklen_t salen;
 
+                r = add_local_outbound_by_prefsrc(&list, &n_list, i, addresses, n_addresses);
+                if (r > 0 || r == -EHOSTUNREACH)
+                        continue;
+                if (r < 0)
+                        return r;
+
                 fd = socket(i->family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
                 if (fd < 0)
                         return -errno;

diff --git a/src/shared/local-addresses.h b/src/shared/local-addresses.h
index 42abca783815e78451ed2c5bd95fe2281d2171ae..9e8374fa6f3acfb5c9df775f8090594cc9304f03 100644 (file)
--- a/src/shared/local-addresses.h
+++ b/src/shared/local-addresses.h
@@ -12,6 +12,7 @@ struct local_address {
         uint32_t weight;
         int family;
         union in_addr_union address;
+        union in_addr_union prefsrc;
 };
 
 bool has_local_address(const struct local_address *addresses, size_t n_addresses, const struct local_address *needle);