Merge pull request #1174 from giuseppe/rootless-use-current-cgroupfs

cgroup: cgroupfs attempt new sibling cgroup

Author: flouthoc

src/libcrun/cgroup-cgroupfs.c

@@ -40,15 +40,14 @@
 static char *
 make_cgroup_path (const char *path, const char *id)
 {
-  const char *cgroup_path = path;
   char *ret;
 
-  if (cgroup_path == NULL)
+  if (path == NULL)
     xasprintf (&ret, "/%s", id);
-  else if (cgroup_path[0] == '/')
-    ret = xstrdup (cgroup_path);
+  else if (path[0] == '/')
+    ret = xstrdup (path);
   else
-    xasprintf (&ret, "/%s", cgroup_path);
+    xasprintf (&ret, "/%s", path);
 
   return ret;
 }
@@ -87,6 +86,23 @@ libcrun_precreate_cgroup_cgroupfs (struct libcrun_cgroup_args *args, int *dirfd,
   return 0;
 }
 
+static int
+make_new_sibling_cgroup (char **out, const char *id, libcrun_error_t *err)
+{
+  cleanup_free char *current_cgroup = NULL;
+  char *dir;
+  int ret;
+
+  ret = libcrun_get_current_unified_cgroup (&current_cgroup, false, err);
+  if (UNLIKELY (ret < 0))
+    return ret;
+
+  dir = dirname (current_cgroup);
+
+  append_paths (out, err, dir, id, NULL);
+  return 0;
+}
+
 static int
 libcrun_cgroup_enter_cgroupfs (struct libcrun_cgroup_args *args, struct libcrun_cgroup_status *out, libcrun_error_t *err)
 {
@@ -105,7 +121,30 @@ libcrun_cgroup_enter_cgroupfs (struct libcrun_cgroup_args *args, struct libcrun_
 
       ret = enable_controllers (out->path, err);
       if (UNLIKELY (ret < 0))
-        return ret;
+        {
+          /* If the generated path cannot be used attempt to create the new cgroup
+             as a sibling of the current one.  */
+          if (args->cgroup_path == NULL)
+            {
+              libcrun_error_t tmp_err = NULL;
+              int tmp_ret;
+
+              free (out->path);
+              out->path = NULL;
+
+              tmp_ret = make_new_sibling_cgroup (&out->path, args->id, &tmp_err);
+              if (UNLIKELY (tmp_ret < 0))
+                {
+                  crun_error_release (&tmp_err);
+                  return ret;
+                }
+
+              crun_error_release (err);
+              ret = enable_controllers (out->path, err);
+            }
+          if (UNLIKELY (ret < 0))
+            return ret;
+        }
     }
 
   /* The cgroup was already joined, nothing more left to do.  */

src/libcrun/cgroup-utils.c

@@ -151,7 +151,7 @@ move_process_to_cgroup (pid_t pid, const char *subsystem, const char *path, libc
 }
 
 int
-libcrun_get_current_unified_cgroup (char **path, libcrun_error_t *err)
+libcrun_get_current_unified_cgroup (char **path, bool absolute, libcrun_error_t *err)
 {
   cleanup_free char *content = NULL;
   size_t content_size;
@@ -172,7 +172,11 @@ libcrun_get_current_unified_cgroup (char **path, libcrun_error_t *err)
     return crun_make_error (err, 0, "cannot parse /proc/self/cgroup");
   *to = '\0';
 
-  return append_paths (path, err, CGROUP_ROOT, from, NULL);
+  if (absolute)
+    return append_paths (path, err, CGROUP_ROOT, from, NULL);
+
+  *path = xstrdup (from);
+  return 0;
 }
 
 #ifndef CGROUP2_SUPER_MAGIC

src/libcrun/cgroup-utils.h

@@ -26,7 +26,7 @@ int libcrun_move_process_to_cgroup (pid_t pid, pid_t init_pid, char *path, libcr
 
 int libcrun_cgroups_create_symlinks (int dirfd, libcrun_error_t *err);
 
-int libcrun_get_current_unified_cgroup (char **path, libcrun_error_t *err);
+int libcrun_get_current_unified_cgroup (char **path, bool absolute, libcrun_error_t *err);
 
 int libcrun_get_cgroup_mode (libcrun_error_t *err);
 

src/libcrun/linux.c

@@ -2546,7 +2546,7 @@ libcrun_set_mounts (struct container_entrypoint_s *entrypoint_args, libcrun_cont
   if (cgroup_mode == CGROUP_MODE_UNIFIED)
     {
       /* Read the cgroup path before we enter the cgroupns.  */
-      ret = libcrun_get_current_unified_cgroup (&unified_cgroup_path, err);
+      ret = libcrun_get_current_unified_cgroup (&unified_cgroup_path, true, err);
       if (UNLIKELY (ret < 0))
         return ret;
     }