bus: when connecting to a container's kdbus instance, enter namespace first

Previously we'd open the connection in the originating namespace, which
meant most peers of the bus would not be able to make sense of the
PID/UID/... identity of us since we didn't exist in the namespace they
run in. However they require this identity for privilege decisions,
hence disallowing access to anything from the host.

Instead, when connecting to a container, create a temporary subprocess,
make it join the container's namespace and then connect from there to
the kdbus instance. This is similar to how we do it for socket
conections already.

THis also unifies the namespacing code used by machinectl and the bus
APIs.

1 files changed, 61 insertions, 8 deletions

diff --git a/src/libsystemd-bus/sd-bus.c b/src/libsystemd-bus/sd-bus.c
index 932bf226c5..4eaceeff04 100644
--- a/src/libsystemd-bus/sd-bus.c
+++ b/src/libsystemd-bus/sd-bus.c
@@ -740,7 +740,7 @@ static int parse_kernel_address(sd_bus *b, const char **p, char **guid) {
         return 0;
 }
 
-static int parse_container_address(sd_bus *b, const char **p, char **guid) {
+static int parse_container_unix_address(sd_bus *b, const char **p, char **guid) {
         _cleanup_free_ char *machine = NULL;
         int r;
 
@@ -782,6 +782,49 @@ static int parse_container_address(sd_bus *b, const char **p, char **guid) {
         return 0;
 }
 
+static int parse_container_kernel_address(sd_bus *b, const char **p, char **guid) {
+        _cleanup_free_ char *machine = NULL;
+        int r;
+
+        assert(b);
+        assert(p);
+        assert(*p);
+        assert(guid);
+
+        while (**p != 0 && **p != ';') {
+                r = parse_address_key(p, "guid", guid);
+                if (r < 0)
+                        return r;
+                else if (r > 0)
+                        continue;
+
+                r = parse_address_key(p, "machine", &machine);
+                if (r < 0)
+                        return r;
+                else if (r > 0)
+                        continue;
+
+                skip_address_key(p);
+        }
+
+        if (!machine)
+                return -EINVAL;
+
+        if (!filename_is_safe(machine))
+                return -EINVAL;
+
+        free(b->machine);
+        b->machine = machine;
+        machine = NULL;
+
+        free(b->kernel);
+        b->kernel = strdup("/dev/kdbus/0-system/bus");
+        if (!b->kernel)
+                return -ENOMEM;
+
+        return 0;
+}
+
 static void bus_reset_parsed_address(sd_bus *b) {
         assert(b);
 
@@ -855,10 +898,18 @@ static int bus_parse_next_address(sd_bus *b) {
                                 return r;
 
                         break;
-                } else if (startswith(a, "x-container:")) {
+                } else if (startswith(a, "x-container-unix:")) {
+
+                        a += 17;
+                        r = parse_container_unix_address(b, &a, &guid);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                } else if (startswith(a, "x-container-kernel:")) {
 
-                        a += 12;
-                        r = parse_container_address(b, &a, &guid);
+                        a += 19;
+                        r = parse_container_kernel_address(b, &a, &guid);
                         if (r < 0)
                                 return r;
 
@@ -892,10 +943,12 @@ static int bus_start_address(sd_bus *b) {
 
                 if (b->exec_path)
                         r = bus_socket_exec(b);
+                else if (b->machine && b->kernel)
+                        r = bus_container_connect_kernel(b);
+                else if (b->machine && b->sockaddr.sa.sa_family != AF_UNSPEC)
+                        r = bus_container_connect_socket(b);
                 else if (b->kernel)
                         r = bus_kernel_connect(b);
-                else if (b->machine)
-                        r = bus_container_connect(b);
                 else if (b->sockaddr.sa.sa_family != AF_UNSPEC)
                         r = bus_socket_connect(b);
                 else
@@ -1144,9 +1197,9 @@ _public_ int sd_bus_open_system_container(const char *machine, sd_bus **ret) {
                 return -ENOMEM;
 
 #ifdef ENABLE_KDBUS
-        p = strjoin("kernel:path=/dev/kdbus/ns/machine-", e, "/0-system/bus;x-container:machine=", e, NULL);
+        p = strjoin("x-container-kernel:machine=", e, ";x-container-unix:machine=", e, NULL);
 #else
-        p = strjoin("x-container:machine=", e, NULL);
+        p = strjoin("x-container-unix:machine=", e, NULL);
 #endif
         if (!p)
                 return -ENOMEM;