networkd: limit the number of routes to the kernel limit (#4007)

Fixes #3922.

1 files changed, 31 insertions, 4 deletions

diff --git a/src/network/networkd-route.c b/src/network/networkd-route.c
index b197a5da6b..6f60ee5e31 100644
--- a/src/network/networkd-route.c
+++ b/src/network/networkd-route.c
@@ -26,10 +26,37 @@
 #include "parse-util.h"
 #include "set.h"
 #include "string-util.h"
+#include "sysctl-util.h"
 #include "util.h"
 
-#define ROUTES_PER_LINK_MAX 2048U
-#define STATIC_ROUTES_PER_NETWORK_MAX 1024U
+#define ROUTES_DEFAULT_MAX_PER_FAMILY 4096U
+
+static unsigned routes_max(void) {
+        static thread_local unsigned cached = 0;
+
+        _cleanup_free_ char *s4 = NULL, *s6 = NULL;
+        unsigned val4 = ROUTES_DEFAULT_MAX_PER_FAMILY, val6 = ROUTES_DEFAULT_MAX_PER_FAMILY;
+
+        if (cached > 0)
+                return cached;
+
+        if (sysctl_read("net/ipv4/route/max_size", &s4) >= 0) {
+                truncate_nl(s4);
+                if (safe_atou(s4, &val4) >= 0 &&
+                    val4 == 2147483647U)
+                        /* This is the default "no limit" value in the kernel */
+                        val4 = ROUTES_DEFAULT_MAX_PER_FAMILY;
+        }
+
+        if (sysctl_read("net/ipv6/route/max_size", &s6) >= 0) {
+                truncate_nl(s6);
+                (void) safe_atou(s6, &val6);
+        }
+
+        cached = MAX(ROUTES_DEFAULT_MAX_PER_FAMILY, val4) +
+                 MAX(ROUTES_DEFAULT_MAX_PER_FAMILY, val6);
+        return cached;
+}
 
 int route_new(Route **ret) {
         _cleanup_route_free_ Route *route = NULL;
@@ -67,7 +94,7 @@ int route_new_static(Network *network, unsigned section, Route **ret) {
                 }
         }
 
-        if (network->n_static_routes >= STATIC_ROUTES_PER_NETWORK_MAX)
+        if (network->n_static_routes >= routes_max())
                 return -E2BIG;
 
         r = route_new(&route);
@@ -484,7 +511,7 @@ int route_configure(
         assert(route->family == AF_INET || route->family == AF_INET6);
 
         if (route_get(link, route->family, &route->dst, route->dst_prefixlen, route->tos, route->priority, route->table, NULL) <= 0 &&
-            set_size(link->routes) >= ROUTES_PER_LINK_MAX)
+            set_size(link->routes) >= routes_max())
                 return -E2BIG;
 
         r = sd_rtnl_message_new_route(link->manager->rtnl, &req,