nspawn: cleanup and chown the synced cgroup hierarchy (#4223)

Fixes: #4181

src/basic/cgroup-util.c

@@ -2514,6 +2514,20 @@ int cg_blkio_weight_parse(const char *s, uint64_t *ret) {
         return 0;
 }
 
+bool is_cgroup_fs(const struct statfs *s) {
+        return is_fs_type(s, CGROUP_SUPER_MAGIC) ||
+               is_fs_type(s, CGROUP2_SUPER_MAGIC);
+}
+
+bool fd_is_cgroup_fs(int fd) {
+        struct statfs s;
+
+        if (fstatfs(fd, &s) < 0)
+                return -errno;
+
+        return is_cgroup_fs(&s);
+}
+
 static const char *cgroup_controller_table[_CGROUP_CONTROLLER_MAX] = {
         [CGROUP_CONTROLLER_CPU] = "cpu",
         [CGROUP_CONTROLLER_CPUACCT] = "cpuacct",

src/basic/cgroup-util.h

@@ -23,6 +23,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <sys/statfs.h>
 #include <sys/types.h>
 
 #include "def.h"
@@ -254,3 +255,6 @@ CGroupController cgroup_controller_from_string(const char *s) _pure_;
 int cg_weight_parse(const char *s, uint64_t *ret);
 int cg_cpu_shares_parse(const char *s, uint64_t *ret);
 int cg_blkio_weight_parse(const char *s, uint64_t *ret);
+
+bool is_cgroup_fs(const struct statfs *s);
+bool fd_is_cgroup_fs(int fd);

src/basic/rm-rf.c

@@ -27,6 +27,7 @@
 #include <unistd.h>
 
 #include "btrfs-util.h"
+#include "cgroup-util.h"
 #include "fd-util.h"
 #include "log.h"
 #include "macro.h"
@@ -36,9 +37,14 @@
 #include "stat-util.h"
 #include "string-util.h"
 
+static bool is_physical_fs(const struct statfs *sfs) {
+        return !is_temporary_fs(sfs) && !is_cgroup_fs(sfs);
+}
+
 int rm_rf_children(int fd, RemoveFlags flags, struct stat *root_dev) {
         _cleanup_closedir_ DIR *d = NULL;
         int ret = 0, r;
+        struct statfs sfs;
 
         assert(fd >= 0);
 
@@ -47,13 +53,13 @@ int rm_rf_children(int fd, RemoveFlags flags, struct stat *root_dev) {
 
         if (!(flags & REMOVE_PHYSICAL)) {
 
-                r = fd_is_temporary_fs(fd);
+                r = fstatfs(fd, &sfs);
                 if (r < 0) {
                         safe_close(fd);
-                        return r;
+                        return -errno;
                 }
 
-                if (!r) {
+                if (is_physical_fs(&sfs)) {
                         /* We refuse to clean physical file systems
                          * with this call, unless explicitly
                          * requested. This is extra paranoia just to
@@ -210,7 +216,7 @@ int rm_rf(const char *path, RemoveFlags flags) {
                         if (statfs(path, &s) < 0)
                                 return -errno;
 
-                        if (!is_temporary_fs(&s)) {
+                        if (is_physical_fs(&s)) {
                                 log_error("Attempted to remove disk file system, and we can't allow that.");
                                 return -EPERM;
                         }