[patch 4/9] unprivileged mounts: propagate error values from clone_mnt

[Miklos Szeredi <miklos@szeredi.hu>]

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From: Miklos Szeredi <mszeredi@suse.cz>

Allow clone_mnt() to return errors other than ENOMEM.  This will be used for
returning a different error value when the number of user mounts goes over the
limit.

Fix copy_tree() to return EPERM for unbindable mounts.

Don't propagate further from dup_mnt_ns() as that copy_tree() can only fail
with -ENOMEM.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2008-01-04 13:47:09.000000000 +0100
+++ linux/fs/namespace.c	2008-01-04 13:47:49.000000000 +0100
@@ -512,41 +512,42 @@ static struct vfsmount *clone_mnt(struct
 	struct super_block *sb = old->mnt_sb;
 	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
 
-	if (mnt) {
-		mnt->mnt_flags = old->mnt_flags;
-		atomic_inc(&sb->s_active);
-		mnt->mnt_sb = sb;
-		mnt->mnt_root = dget(root);
-		mnt->mnt_mountpoint = mnt->mnt_root;
-		mnt->mnt_parent = mnt;
-
-		/* don't copy the MNT_USER flag */
-		mnt->mnt_flags &= ~MNT_USER;
-		if (flag & CL_SETUSER)
-			set_mnt_user(mnt);
-
-		if (flag & CL_SLAVE) {
-			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
-			mnt->mnt_master = old;
-			CLEAR_MNT_SHARED(mnt);
-		} else if (!(flag & CL_PRIVATE)) {
-			if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
-				list_add(&mnt->mnt_share, &old->mnt_share);
-			if (IS_MNT_SLAVE(old))
-				list_add(&mnt->mnt_slave, &old->mnt_slave);
-			mnt->mnt_master = old->mnt_master;
-		}
-		if (flag & CL_MAKE_SHARED)
-			set_mnt_shared(mnt);
+	if (!mnt)
+		return ERR_PTR(-ENOMEM);
 
-		/* stick the duplicate mount on the same expiry list
-		 * as the original if that was on one */
-		if (flag & CL_EXPIRE) {
-			spin_lock(&vfsmount_lock);
-			if (!list_empty(&old->mnt_expire))
-				list_add(&mnt->mnt_expire, &old->mnt_expire);
-			spin_unlock(&vfsmount_lock);
-		}
+	mnt->mnt_flags = old->mnt_flags;
+	atomic_inc(&sb->s_active);
+	mnt->mnt_sb = sb;
+	mnt->mnt_root = dget(root);
+	mnt->mnt_mountpoint = mnt->mnt_root;
+	mnt->mnt_parent = mnt;
+
+	/* don't copy the MNT_USER flag */
+	mnt->mnt_flags &= ~MNT_USER;
+	if (flag & CL_SETUSER)
+		set_mnt_user(mnt);
+
+	if (flag & CL_SLAVE) {
+		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
+		mnt->mnt_master = old;
+		CLEAR_MNT_SHARED(mnt);
+	} else if (!(flag & CL_PRIVATE)) {
+		if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
+			list_add(&mnt->mnt_share, &old->mnt_share);
+		if (IS_MNT_SLAVE(old))
+			list_add(&mnt->mnt_slave, &old->mnt_slave);
+		mnt->mnt_master = old->mnt_master;
+	}
+	if (flag & CL_MAKE_SHARED)
+		set_mnt_shared(mnt);
+
+	/* stick the duplicate mount on the same expiry list
+	 * as the original if that was on one */
+	if (flag & CL_EXPIRE) {
+		spin_lock(&vfsmount_lock);
+		if (!list_empty(&old->mnt_expire))
+			list_add(&mnt->mnt_expire, &old->mnt_expire);
+		spin_unlock(&vfsmount_lock);
 	}
 	return mnt;
 }
@@ -1021,11 +1022,11 @@ struct vfsmount *copy_tree(struct vfsmou
 	struct nameidata nd;
 
 	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
-		return NULL;
+		return ERR_PTR(-EPERM);
 
 	res = q = clone_mnt(mnt, dentry, flag);
-	if (!q)
-		goto Enomem;
+	if (IS_ERR(q))
+		goto error;
 	q->mnt_mountpoint = mnt->mnt_mountpoint;
 
 	p = mnt;
@@ -1046,8 +1047,8 @@ struct vfsmount *copy_tree(struct vfsmou
 			nd.path.mnt = q;
 			nd.path.dentry = p->mnt_mountpoint;
 			q = clone_mnt(p, p->mnt_root, flag);
-			if (!q)
-				goto Enomem;
+			if (IS_ERR(q))
+				goto error;
 			spin_lock(&vfsmount_lock);
 			list_add_tail(&q->mnt_list, &res->mnt_list);
 			attach_mnt(q, &nd);
@@ -1055,7 +1056,7 @@ struct vfsmount *copy_tree(struct vfsmou
 		}
 	}
 	return res;
-Enomem:
+ error:
 	if (res) {
 		LIST_HEAD(umount_list);
 		spin_lock(&vfsmount_lock);
@@ -1063,7 +1064,7 @@ Enomem:
 		spin_unlock(&vfsmount_lock);
 		release_mounts(&umount_list);
 	}
-	return NULL;
+	return q;
 }
 
 struct vfsmount *collect_mounts(struct vfsmount *mnt, struct dentry *dentry)
@@ -1262,13 +1263,13 @@ static int do_loopback(struct nameidata 
 		goto out;
 
 	clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
-	err = -ENOMEM;
 	if (flags & MS_REC)
 		mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
 	else
 		mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
 
-	if (!mnt)
+	err = PTR_ERR(mnt);
+	if (IS_ERR(mnt))
 		goto out;
 
 	err = graft_tree(mnt, nd);
@@ -1840,7 +1841,7 @@ static struct mnt_namespace *dup_mnt_ns(
 	/* First pass: copy the tree topology */
 	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
 					CL_COPY_ALL | CL_EXPIRE);
-	if (!new_ns->root) {
+	if (IS_ERR(new_ns->root)) {
 		up_write(&namespace_sem);
 		kfree(new_ns);
 		return ERR_PTR(-ENOMEM);;
Index: linux/fs/pnode.c
===================================================================
--- linux.orig/fs/pnode.c	2008-01-04 13:45:46.000000000 +0100
+++ linux/fs/pnode.c	2008-01-04 13:47:49.000000000 +0100
@@ -189,8 +189,9 @@ int propagate_mnt(struct vfsmount *dest_
 
 		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 
-		if (!(child = copy_tree(source, source->mnt_root, type))) {
-			ret = -ENOMEM;
+		child = copy_tree(source, source->mnt_root, type);
+		if (IS_ERR(child)) {
+			ret = PTR_ERR(child);
 			list_splice(tree_list, tmp_list.prev);
 			goto out;
 		}

--