firewall-util: introduce context structure

for planned nft backend we have three choices:

- open/close a new nfnetlink socket for every operation
- keep a nfnetlink socket open internally
- expose a opaque fw_ctx and stash all internal data here.

Originally I opted for the 2nd option, but during review it was
suggested to avoid static storage duration because of perceived
problems with threaded applications.

This adds fw_ctx and new/free functions, then converts the existing api
and nspawn and networkd to use it.

src/nspawn/nspawn-expose-ports.c

@@ -82,7 +82,7 @@ void expose_port_free_all(ExposePort *p) {
         }
 }
 
-int expose_port_flush(ExposePort* l, union in_addr_union *exposed) {
+int expose_port_flush(FirewallContext **fw_ctx, ExposePort* l, union in_addr_union *exposed) {
         ExposePort *p;
         int r, af = AF_INET;
 
@@ -97,7 +97,8 @@ int expose_port_flush(ExposePort* l, union in_addr_union *exposed) {
         log_debug("Lost IP address.");
 
         LIST_FOREACH(ports, p, l) {
-                r = fw_add_local_dnat(false,
+                r = fw_add_local_dnat(fw_ctx,
+                                      false,
                                       af,
                                       p->protocol,
                                       p->host_port,
@@ -112,7 +113,7 @@ int expose_port_flush(ExposePort* l, union in_addr_union *exposed) {
         return 0;
 }
 
-int expose_port_execute(sd_netlink *rtnl, ExposePort *l, union in_addr_union *exposed) {
+int expose_port_execute(sd_netlink *rtnl, FirewallContext **fw_ctx, ExposePort *l, union in_addr_union *exposed) {
         _cleanup_free_ struct local_address *addresses = NULL;
         union in_addr_union new_exposed;
         ExposePort *p;
@@ -136,7 +137,7 @@ int expose_port_execute(sd_netlink *rtnl, ExposePort *l, union in_addr_union *ex
                 addresses[0].scope < RT_SCOPE_LINK;
 
         if (!add)
-                return expose_port_flush(l, exposed);
+                return expose_port_flush(fw_ctx, l, exposed);
 
         new_exposed = addresses[0].address;
         if (in_addr_equal(af, exposed, &new_exposed))
@@ -150,7 +151,8 @@ int expose_port_execute(sd_netlink *rtnl, ExposePort *l, union in_addr_union *ex
 
         LIST_FOREACH(ports, p, l) {
 
-                r = fw_add_local_dnat(true,
+                r = fw_add_local_dnat(fw_ctx,
+                                      true,
                                       af,
                                       p->protocol,
                                       p->host_port,

src/nspawn/nspawn-expose-ports.h

@@ -3,6 +3,8 @@
 
 #include <inttypes.h>
 
+#include "firewall-util.h"
+
 #include "sd-event.h"
 #include "sd-netlink.h"
 
@@ -22,5 +24,5 @@ int expose_port_parse(ExposePort **l, const char *s);
 int expose_port_watch_rtnl(sd_event *event, int recv_fd, sd_netlink_message_handler_t handler, void *userdata, sd_netlink **ret);
 int expose_port_send_rtnl(int send_fd);
 
-int expose_port_execute(sd_netlink *rtnl, ExposePort *l, union in_addr_union *exposed);
-int expose_port_flush(ExposePort* l, union in_addr_union *exposed);
+int expose_port_execute(sd_netlink *rtnl, FirewallContext **fw_ctx, ExposePort *l, union in_addr_union *exposed);
+int expose_port_flush(FirewallContext **fw_ctx, ExposePort* l, union in_addr_union *exposed);

src/nspawn/nspawn.c

@@ -2474,14 +2474,19 @@ static int setup_kmsg(int kmsg_socket) {
         return 0;
 }
 
+struct ExposeArgs {
+        union in_addr_union address;
+        struct FirewallContext *fw_ctx;
+};
+
 static int on_address_change(sd_netlink *rtnl, sd_netlink_message *m, void *userdata) {
-        union in_addr_union *exposed = userdata;
+        struct ExposeArgs *args = userdata;
 
         assert(rtnl);
         assert(m);
-        assert(exposed);
+        assert(args);
 
-        expose_port_execute(rtnl, arg_expose_ports, exposed);
+        expose_port_execute(rtnl, &args->fw_ctx, arg_expose_ports, &args->address);
         return 0;
 }
 
@@ -4466,7 +4471,7 @@ static int run_container(
                bool secondary,
                FDSet *fds,
                char veth_name[IFNAMSIZ], bool *veth_created,
-               union in_addr_union *exposed,
+               struct ExposeArgs *expose_args,
                int *master, pid_t *pid, int *ret) {
 
         static const struct sigaction sa = {
@@ -4895,11 +4900,11 @@ static int run_container(
         (void) sd_event_add_signal(event, NULL, SIGCHLD, on_sigchld, PID_TO_PTR(*pid));
 
         if (arg_expose_ports) {
-                r = expose_port_watch_rtnl(event, rtnl_socket_pair[0], on_address_change, exposed, &rtnl);
+                r = expose_port_watch_rtnl(event, rtnl_socket_pair[0], on_address_change, expose_args, &rtnl);
                 if (r < 0)
                         return r;
 
-                (void) expose_port_execute(rtnl, arg_expose_ports, exposed);
+                (void) expose_port_execute(rtnl, &expose_args->fw_ctx, arg_expose_ports, &expose_args->address);
         }
 
         rtnl_socket_pair[0] = safe_close(rtnl_socket_pair[0]);
@@ -5026,7 +5031,7 @@ static int run_container(
                 return 0; /* finito */
         }
 
-        expose_port_flush(arg_expose_ports, exposed);
+        expose_port_flush(&expose_args->fw_ctx, arg_expose_ports, &expose_args->address);
 
         (void) remove_veth_links(veth_name, arg_network_veth_extra);
         *veth_created = false;
@@ -5155,12 +5160,13 @@ static int run(int argc, char *argv[]) {
         _cleanup_fdset_free_ FDSet *fds = NULL;
         int r, n_fd_passed, ret = EXIT_SUCCESS;
         char veth_name[IFNAMSIZ] = "";
-        union in_addr_union exposed = {};
+        struct ExposeArgs expose_args = {};
         _cleanup_(release_lock_file) LockFile tree_global_lock = LOCK_FILE_INIT, tree_local_lock = LOCK_FILE_INIT;
         char tmprootdir[] = "/tmp/nspawn-root-XXXXXX";
         _cleanup_(loop_device_unrefp) LoopDevice *loop = NULL;
         _cleanup_(decrypted_image_unrefp) DecryptedImage *decrypted_image = NULL;
         _cleanup_(dissected_image_unrefp) DissectedImage *dissected_image = NULL;
+        _cleanup_(fw_ctx_freep) FirewallContext *fw_ctx = NULL;
         pid_t pid = 0;
 
         log_parse_environment();
@@ -5517,12 +5523,20 @@ static int run(int argc, char *argv[]) {
                 goto finish;
         }
 
+        if (arg_expose_ports) {
+                r = fw_ctx_new(&fw_ctx);
+                if (r < 0) {
+                        log_error_errno(r, "Cannot expose configured ports, firewall initialization failed: %m");
+                        goto finish;
+                }
+                expose_args.fw_ctx = fw_ctx;
+        }
         for (;;) {
                 r = run_container(dissected_image,
                                   secondary,
                                   fds,
                                   veth_name, &veth_created,
-                                  &exposed, &master,
+                                  &expose_args, &master,
                                   &pid, &ret);
                 if (r <= 0)
                         break;
@@ -5572,7 +5586,7 @@ finish:
                 (void) rm_rf(p, REMOVE_ROOT);
         }
 
-        expose_port_flush(arg_expose_ports, &exposed);
+        expose_port_flush(&fw_ctx, arg_expose_ports, &expose_args.address);
 
         if (veth_created)
                 (void) remove_veth_links(veth_name, arg_network_veth_extra);