Commit f2d0a123 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

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: e0c9c0af mnt: Update detach_mounts to leave mounts connected
Fixes: ce07d891 mnt: Honor MNT_LOCKED when detaching mounts
Cc: stable@vger.kernel.org
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent d770e558

fs/namespace.c

+31 −4
Original line number Diff line number Diff line
@@ -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);

fs/pnode.h

+0 −2
Original line number Diff line number Diff line
@@ -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

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