mnt: Clarify and correct the disconnect logic in umount_tree

rmdir mntpoint will result in an infinite loop when there is
a mount locked on the mountpoint in another mount namespace.

This is because the logic to test to see if a mount should
be disconnected in umount_tree is buggy.

Move the logic to decide if a mount should remain connected to
it's mountpoint into it's own function disconnect_mount so that
clarity of expression instead of terseness of expression becomes
a virtue.

When the conditions where it is invalid to leave a mount connected
are first ruled out, the logic for deciding if a mount should
be disconnected becomes much clearer and simpler.

Fixes: e0c9c0afd2fc958ffa34b697972721d81df8a56f mnt: Update detach_mounts to leave mounts connected
Fixes: ce07d891a0891d3c0d0c2d73d577490486b809e1 mnt: Honor MNT_LOCKED when detaching mounts
Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/fs/namespace.c b/fs/namespace.c
index c7cb8a526c05fbaa5ba18934cd04eda1eb2a6e60..7829eab0b7063ce1f82a0436f77f7a5639cfb485 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1361,6 +1361,36 @@ enum umount_tree_flags {
        UMOUNT_PROPAGATE = 2,
        UMOUNT_CONNECTED = 4,
 };
+
+static bool disconnect_mount(struct mount *mnt, enum umount_tree_flags how)
+{
+       /* Leaving mounts connected is only valid for lazy umounts */
+       if (how & UMOUNT_SYNC)
+               return true;
+
+       /* A mount without a parent has nothing to be connected to */
+       if (!mnt_has_parent(mnt))
+               return true;
+
+       /* Because the reference counting rules change when mounts are
+        * unmounted and connected, umounted mounts may not be
+        * connected to mounted mounts.
+        */
+       if (!(mnt->mnt_parent->mnt.mnt_flags & MNT_UMOUNT))
+               return true;
+
+       /* Has it been requested that the mount remain connected? */
+       if (how & UMOUNT_CONNECTED)
+               return false;
+
+       /* Is the mount locked such that it needs to remain connected? */
+       if (IS_MNT_LOCKED(mnt))
+               return false;
+
+       /* By default disconnect the mount */
+       return true;
+}
+
 /*
  * mount_lock must be held
  * namespace_sem must be held for write
@@ -1398,10 +1428,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
                if (how & UMOUNT_SYNC)
                        p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 
-               disconnect = !(((how & UMOUNT_CONNECTED) &&
-                               mnt_has_parent(p) &&
-                               (p->mnt_parent->mnt.mnt_flags & MNT_UMOUNT)) ||
-                              IS_MNT_LOCKED_AND_LAZY(p));
+               disconnect = disconnect_mount(p, how);
 
                pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
                                 disconnect ? &unmounted : NULL);

diff --git a/fs/pnode.h b/fs/pnode.h
index 7114ce6e6b9ef038f415550b925ac50a95be978c..0fcdbe7ca6480e7950092cfd0dc7d0ce431ef548 100644 (file)
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -20,8 +20,6 @@
 #define SET_MNT_MARK(m) ((m)->mnt.mnt_flags |= MNT_MARKED)
 #define CLEAR_MNT_MARK(m) ((m)->mnt.mnt_flags &= ~MNT_MARKED)
 #define IS_MNT_LOCKED(m) ((m)->mnt.mnt_flags & MNT_LOCKED)
-#define IS_MNT_LOCKED_AND_LAZY(m) \
-       (((m)->mnt.mnt_flags & (MNT_LOCKED|MNT_SYNC_UMOUNT)) == MNT_LOCKED)
 
 #define CL_EXPIRE              0x01
 #define CL_SLAVE               0x02