Revert "selinux: split up mac_selinux_have() from mac_selinux_use()"

This reverts commit 6355e75610.

The previously mentioned commit inadvertently broke a lot of SELinux related
functionality for both unprivileged users and systemd instances running as
MANAGER_USER.  In particular, setting the correct SELinux context after a User=
directive is used would fail to work since we attempt to set the security
context after changing UID.  Additionally, it causes activated socket units to
be mislabeled for systemd --user processes since setsockcreatecon() would never
be called.

Reverting this fixes the issues with labeling outlined above, and reinstates
SELinux access checks on unprivileged user services.

src/basic/selinux-util.c

@@ -53,7 +53,7 @@ static struct selabel_handle *label_hnd = NULL;
 #define log_enforcing(...) log_full(security_getenforce() == 1 ? LOG_ERR : LOG_DEBUG, __VA_ARGS__)
 #endif
 
-bool mac_selinux_have(void) {
+bool mac_selinux_use(void) {
 #ifdef HAVE_SELINUX
         if (cached_use < 0)
                 cached_use = is_selinux_enabled() > 0;
@@ -64,16 +64,6 @@ bool mac_selinux_have(void) {
 #endif
 }
 
-bool mac_selinux_use(void) {
-        if (!mac_selinux_have())
-                return false;
-
-        /* Never try to configure SELinux features if we aren't
-         * root */
-
-        return getuid() == 0;
-}
-
 void mac_selinux_retest(void) {
 #ifdef HAVE_SELINUX
         cached_use = -1;
@@ -205,7 +195,7 @@ int mac_selinux_get_create_label_from_exe(const char *exe, char **label) {
         assert(exe);
         assert(label);
 
-        if (!mac_selinux_have())
+        if (!mac_selinux_use())
                 return -EOPNOTSUPP;
 
         r = getcon_raw(&mycon);
@@ -231,7 +221,7 @@ int mac_selinux_get_our_label(char **label) {
         assert(label);
 
 #ifdef HAVE_SELINUX
-        if (!mac_selinux_have())
+        if (!mac_selinux_use())
                 return -EOPNOTSUPP;
 
         r = getcon_raw(label);
@@ -255,7 +245,7 @@ int mac_selinux_get_child_mls_label(int socket_fd, const char *exe, const char *
         assert(exe);
         assert(label);
 
-        if (!mac_selinux_have())
+        if (!mac_selinux_use())
                 return -EOPNOTSUPP;
 
         r = getcon_raw(&mycon);
@@ -310,7 +300,7 @@ char* mac_selinux_free(char *label) {
         if (!label)
                 return NULL;
 
-        if (!mac_selinux_have())
+        if (!mac_selinux_use())
                 return NULL;
 
 

src/basic/selinux-util.h

@@ -26,7 +26,6 @@
 #include "macro.h"
 
 bool mac_selinux_use(void);
-bool mac_selinux_have(void);
 void mac_selinux_retest(void);
 
 int mac_selinux_init(void);