nspawn: Drop CAP_NET_BIND_SERVICE when in userns but not in netns

If we're in a user namespace but not unsharing the network namespace,
we won't be able to bind any privileged ports even with
CAP_NET_BIND_SERVICE, so let's drop it from the retained capabilities
so services can condition themselves on that.

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 25f77509124b70bda1836575fdfd6970c601397a..f16d9506eb398cf976ebe5bff86d0c29a9b30591 100644 (file)
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -1717,7 +1717,16 @@ static int parse_argv(int argc, char *argv[]) {
                  * --directory=". */
                 arg_directory = TAKE_PTR(arg_template);
 
-        arg_caps_retain = (arg_caps_retain | plus | (arg_private_network ? UINT64_C(1) << CAP_NET_ADMIN : 0)) & ~minus;
+        arg_caps_retain |= plus;
+        arg_caps_retain |= arg_private_network ? UINT64_C(1) << CAP_NET_ADMIN : 0;
+
+        /* If we're not unsharing the network namespace and are unsharing the user namespace, we won't have
+         * permissions to bind ports in the container, so let's drop the CAP_NET_BIND_SERVICE capability to
+         * indicate that. */
+        if (!arg_private_network && arg_userns_mode != USER_NAMESPACE_NO && arg_uid_shift > 0)
+                arg_caps_retain &= ~(UINT64_C(1) << CAP_NET_BIND_SERVICE);
+
+        arg_caps_retain &= ~minus;
 
         /* Make sure to parse environment before we reset the settings mask below */
         r = parse_environment();