1 files changed, 25 insertions, 12 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 64627f883bf2..877e4277f496 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2867,25 +2867,38 @@ bool current_chrooted(void)
         return chrooted;
 }
 
-void update_mnt_policy(struct user_namespace *userns)
+bool fs_fully_visible(struct file_system_type *type)
 {
         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
         struct mount *mnt;
+        bool visible = false;
 
-        down_read(&namespace_sem);
+        if (unlikely(!ns))
+                return false;
+
+        namespace_lock();
         list_for_each_entry(mnt, &ns->list, mnt_list) {
-                switch (mnt->mnt.mnt_sb->s_magic) {
-                case SYSFS_MAGIC:
-                        userns->may_mount_sysfs = true;
-                        break;
-                case PROC_SUPER_MAGIC:
-                        userns->may_mount_proc = true;
-                        break;
+                struct mount *child;
+                if (mnt->mnt.mnt_sb->s_type != type)
+                        continue;
+
+                /* This mount is not fully visible if there are any child mounts
+                 * that cover anything except for empty directories.
+                 */
+                list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
+                        struct inode *inode = child->mnt_mountpoint->d_inode;
+                        if (!S_ISDIR(inode->i_mode))
+                                goto next;
+                        if (inode->i_nlink != 2)
+                                goto next;
                 }
-                if (userns->may_mount_sysfs && userns->may_mount_proc)
-                        break;
+                visible = true;
+                goto found;
+        next:   ;
         }
-        up_read(&namespace_sem);
+found:
+        namespace_unlock();
+        return visible;
 }
 
 static void *mntns_get(struct task_struct *task)