[PATCH] namespace fix

After

    # mount --rbind /tmp /mnt

(on 2.5.68) I have a corrupted namespace. Umounting /mnt fails,
and /proc/mounts contains

    ...
    /dev/root /mnt ext3 rw 0 0
    proc /mnt/proc proc rw 0 0
    usbfs /mnt/proc/bus/usb usbfs rw 0 0
    /dev/hdb5 /mnt/usr reiserfs rw 0 0
    ...

where of course no directories /mnt/proc or /mnt/usr exist.

This is caused by the fact that copy_tree() thinks that the dentry
it is called with is the root of the filesystem. If it is not,
confusion arose.

This patch fixes this confusion.

fs/namespace.c

@@ -418,24 +418,41 @@ static int mount_is_safe(struct nameidata *nd)
 #endif
 }
 
+static int
+lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
+{
+	while (1) {
+		if (d == dentry)
+			return 1;
+		if (d == NULL || d == d->d_parent)
+			return 0;
+		d = d->d_parent;
+	}
+}
+
 static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry)
 {
-	struct vfsmount *p, *next, *q, *res;
+	struct vfsmount *res, *p, *q, *r, *s;
+	struct list_head *h;
 	struct nameidata nd;
 
-	p = mnt;
-	res = nd.mnt = q = clone_mnt(p, dentry);
+	res = q = clone_mnt(mnt, dentry);
 	if (!q)
 		goto Enomem;
-	q->mnt_parent = q;
-	q->mnt_mountpoint = p->mnt_mountpoint;
+	q->mnt_mountpoint = mnt->mnt_mountpoint;
 
-	while ( (next = next_mnt(p, mnt)) != NULL) {
-		while (p != next->mnt_parent) {
+	p = mnt;
+	for (h = mnt->mnt_mounts.next; h != &mnt->mnt_mounts; h = h->next) {
+		r = list_entry(h, struct vfsmount, mnt_child);
+		if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
+			continue;
+
+		for (s = r; s; s = next_mnt(s, r)) {
+			while (p != s->mnt_parent) {
 				p = p->mnt_parent;
 				q = q->mnt_parent;
 			}
-		p = next;
+			p = s;
 			nd.mnt = q;
 			nd.dentry = p->mnt_mountpoint;
 			q = clone_mnt(p, p->mnt_root);
@@ -446,8 +463,9 @@ static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry)
 			attach_mnt(q, &nd);
 			spin_unlock(&dcache_lock);
 		}
+	}
 	return res;
-Enomem:
+ Enomem:
 	if (res) {
 		spin_lock(&dcache_lock);
 		umount_tree(res);