From: Al Viro <viro@zeniv.linux.org.uk>
Date: Thu, 8 May 2025 04:09:30 +0000 (-0400)
Subject: do_move_mount(): get rid of 'attached' flag
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ee1ee33ccc1ba0620a77833b2a3e320588701217;p=thirdparty%2Fkernel%2Fstable.git

do_move_mount(): get rid of 'attached' flag

'attached' serves as a proxy for "source is a subtree of our namespace
and not the entirety of anon namespace"; finish massaging it away.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/fs/namespace.c b/fs/namespace.c
index e5f8fde57c997..7c7cc14da1ee2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3600,7 +3600,7 @@ static int do_move_mount(struct path *old_path,
 	struct mount *parent;
 	struct mountpoint *mp;
 	int err;
-	bool attached, beneath = flags & MNT_TREE_BENEATH;
+	bool beneath = flags & MNT_TREE_BENEATH;
 
 	mp = do_lock_mount(new_path, beneath);
 	if (IS_ERR(mp))
@@ -3609,7 +3609,6 @@ static int do_move_mount(struct path *old_path,
 	old = real_mount(old_path->mnt);
 	p = real_mount(new_path->mnt);
 	parent = old->mnt_parent;
-	attached = mnt_has_parent(old);
 	ns = old->mnt_ns;
 
 	err = -EINVAL;
@@ -3622,6 +3621,9 @@ static int do_move_mount(struct path *old_path,
 		/* ... and the target should be in our namespace */
 		if (!check_mnt(p))
 			goto out;
+		/* parent of the source should not be shared */
+		if (IS_MNT_SHARED(parent))
+			goto out;
 	} else {
 		/*
 		 * otherwise the source must be the root of some anon namespace.
@@ -3649,11 +3651,6 @@ static int do_move_mount(struct path *old_path,
 	if (d_is_dir(new_path->dentry) !=
 	    d_is_dir(old_path->dentry))
 		goto out;
-	/*
-	 * Don't move a mount residing in a shared parent.
-	 */
-	if (attached && IS_MNT_SHARED(parent))
-		goto out;
 
 	if (beneath) {
 		err = can_move_mount_beneath(old_path, new_path, mp);
@@ -3686,7 +3683,7 @@ static int do_move_mount(struct path *old_path,
 out:
 	unlock_mount(mp);
 	if (!err) {
-		if (attached) {
+		if (!is_anon_ns(ns)) {
 			mntput_no_expire(parent);
 		} else {
 			/* Make sure we notice when we leak mounts. */