core/namespace: allow using ProtectSubset=pid and ProtectHostname=true together

If a service requests both ProtectSubset=pid and ProtectHostname=true
then it will currently fail to start. The ProcSubset=pid option
instructs systemd to mount procfs for the service with subset=pid which
hides all entries other than /proc/<pid>. Consequently trying to
interact with the two files /proc/sys/kernel/{hostname,domainname}
covered by ProtectHostname=true will fail.

Fix this by only performing this check when ProtectSubset=pid is not
requested. Essentially ProtectSubset=pid implies/provides
ProtectHostname=true.

(cherry picked from commit 1361f015773e3b4d74e382edf1565f3315a3396b)
(cherry picked from commit a727941affa7821592d503c8a5033c92d615f64c)

diff --git a/src/core/namespace.c b/src/core/namespace.c
index e3aebe8b5e8371e1424884d960062663dd3cb540..5961b14f98563eb265c7f76ae01960ea71cc08c0 100644 (file)
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -2115,14 +2115,19 @@ int setup_namespace(
                                 goto finish;
                 }
 
+                /* Note, if proc is mounted with subset=pid then neither of the
+                 * two paths will exist, i.e. they are implicitly protected by
+                 * the mount option. */
                 if (ns_info->protect_hostname) {
                         *(m++) = (MountEntry) {
                                 .path_const = "/proc/sys/kernel/hostname",
                                 .mode = READONLY,
+                                .ignore = ignore_protect_proc,
                         };
                         *(m++) = (MountEntry) {
                                 .path_const = "/proc/sys/kernel/domainname",
                                 .mode = READONLY,
+                                .ignore = ignore_protect_proc,
                         };
                 }