namespace: unify limit behavior on non-directory paths

Despite the name, `Read{Write,Only}Directories=` already allows for
regular file paths to be masked. This commit adds the same behavior
to `InaccessibleDirectories=` and makes it explicit in the doc.
This patch introduces `/run/systemd/inaccessible/{reg,dir,chr,blk,fifo,sock}`
{dile,device}nodes and mounts on the appropriate one the paths specified
in `InacessibleDirectories=`.

Based on Luca's patch from https://github.com/systemd/systemd/pull/3327

3 files changed, 40 insertions, 17 deletions

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index 644b9561b5..4588ecad09 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -1346,12 +1346,12 @@ int bus_exec_context_set_transient_property(
                 if (mode != UNIT_CHECK) {
                         _cleanup_free_ char *joined = NULL;
 
-                        if (streq(name, "ReadWriteDirectories"))
-                                dirs = &c->read_write_dirs;
-                        else if (streq(name, "ReadOnlyDirectories"))
-                                dirs = &c->read_only_dirs;
-                        else /* "InaccessibleDirectories" */
-                                dirs = &c->inaccessible_dirs;
+                        if (STR_IN_SET(name, "ReadWriteDirectories", "ReadWritePaths"))
+                                dirs = &c->read_write_paths;
+                        else if (STR_IN_SET(name, "ReadOnlyDirectories", "ReadOnlyPaths"))
+                                dirs = &c->read_only_paths;
+                        else /* "InaccessiblePaths" */
+                                dirs = &c->inaccessible_paths;
 
                         if (strv_length(l) == 0) {
                                 *dirs = strv_free(*dirs);
diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c
index f9c9b4a91f..5d8ab0ec70 100644
--- a/src/core/mount-setup.c
+++ b/src/core/mount-setup.c
@@ -28,6 +28,7 @@
 #include "cgroup-util.h"
 #include "dev-setup.h"
 #include "efivars.h"
+#include "fs-util.h"
 #include "label.h"
 #include "log.h"
 #include "macro.h"
@@ -403,9 +404,16 @@ int mount_setup(bool loaded_policy) {
          * really needs to stay for good, otherwise software that
          * copied sd-daemon.c into their sources will misdetect
          * systemd. */
-        mkdir_label("/run/systemd", 0755);
-        mkdir_label("/run/systemd/system", 0755);
-        mkdir_label("/run/systemd/inaccessible", 0000);
+        (void) mkdir_label("/run/systemd", 0755);
+        (void) mkdir_label("/run/systemd/system", 0755);
+        (void) mkdir_label("/run/systemd/inaccessible", 0000);
+        /* Set up inaccessible items */
+        (void) mknod("/run/systemd/inaccessible/reg", S_IFREG | 0000, 0);
+        (void) mkdir_label("/run/systemd/inaccessible/dir", 0000);
+        (void) mknod("/run/systemd/inaccessible/chr", S_IFCHR | 0000, makedev(0, 0));
+        (void) mknod("/run/systemd/inaccessible/blk", S_IFBLK | 0000, makedev(0, 0));
+        (void) mkfifo("/run/systemd/inaccessible/fifo", 0000);
+        (void) mknod("/run/systemd/inaccessible/sock", S_IFSOCK | 0000, 0);
 
         return 0;
 }
diff --git a/src/core/namespace.c b/src/core/namespace.c
index 203d122810..e465e825a1 100644
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -278,6 +278,7 @@ static int apply_mount(
 
         const char *what;
         int r;
+        struct stat target;
 
         assert(m);
 
@@ -287,12 +288,22 @@ static int apply_mount(
 
                 /* First, get rid of everything that is below if there
                  * is anything... Then, overmount it with an
-                 * inaccessible directory. */
+                 * inaccessible path. */
                 umount_recursive(m->path, 0);
 
-                what = "/run/systemd/inaccessible";
-                break;
+                r = lstat(m->path, &target);
+                if (r != 0) {
+                        if (m->ignore && errno == ENOENT)
+                                return 0;
+                        return -errno;
+                }
 
+                what = mode_to_inaccessible_node(target.st_mode);
+                if (what == NULL) {
+                        log_debug("File type not supported. Note that symlinks are not allowed");
+                        return -ELOOP;
+                }
+                break;
         case READONLY:
         case READWRITE:
                 /* Nothing to mount here, we just later toggle the
@@ -317,12 +328,16 @@ static int apply_mount(
         assert(what);
 
         r = mount(what, m->path, NULL, MS_BIND|MS_REC, NULL);
-        if (r >= 0)
+        if (r >= 0) {
                 log_debug("Successfully mounted %s to %s", what, m->path);
-        else if (m->ignore && errno == ENOENT)
-                return 0;
-
-        return r;
+                return r;
+        }
+        else {
+                if (m->ignore && errno == ENOENT)
+                        return 0;
+                log_debug("Failed mounting %s to %s: %s", what, m->path, strerror(errno));
+                return -errno;
+        }
 }
 
 static int make_read_only(BindMount *m) {