userns: Better restrictions on when proc and sysfs can be mounted

[karo-tx-linux.git] / fs / namespace.c

diff --git a/fs/namespace.c b/fs/namespace.c
index 64627f883bf2005c835eaa0fad791ebe566ec4a2..877e4277f4962cd1699a9dddcd2e2cec67982928 100644 (file)
--- 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)