mnt: Update detach_mounts to leave mounts connected

Now that it is possible to lazily unmount an entire mount tree and
leave the individual mounts connected to each other add a new flag
UMOUNT_CONNECTED to umount_tree to force this behavior and use
this flag in detach_mounts.

This closes a bug where the deletion of a file or directory could
trigger an unmount and reveal data under a mount point.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index e8f7f8c58c3c..1f4f9dac6e5a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1348,6 +1348,7 @@ static inline void namespace_lock(void)
 enum umount_tree_flags {
         UMOUNT_SYNC = 1,
         UMOUNT_PROPAGATE = 2,
+        UMOUNT_CONNECTED = 4,
 };
 /*
  * mount_lock must be held
@@ -1386,7 +1387,10 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
                 if (how & UMOUNT_SYNC)
                         p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 
-                disconnect = !IS_MNT_LOCKED_AND_LAZY(p);
+                disconnect = !(((how & UMOUNT_CONNECTED) &&
+                                mnt_has_parent(p) &&
+                                (p->mnt_parent->mnt.mnt_flags & MNT_UMOUNT)) ||
+                               IS_MNT_LOCKED_AND_LAZY(p));
 
                 pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
                                  disconnect ? &unmounted : NULL);
@@ -1529,7 +1533,7 @@ void __detach_mounts(struct dentry *dentry)
                                 umount_mnt(p);
                         }
                 }
-                else umount_tree(mnt, 0);
+                else umount_tree(mnt, UMOUNT_CONNECTED);
         }
         unlock_mount_hash();
         put_mountpoint(mp);