[patch 3/5] union-directory: Some checks during namespace changes

[Miklos Szeredi <miklos@xxxxxxxxxx>]

From: Jan Blunck <jblunck@xxxxxxx>

Add some additional checks when mounting something into an union.

Signed-off-by: Jan Blunck <jblunck@xxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 fs/namespace.c |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

Index: linux-2.6/fs/namespace.c
===================================================================
--- linux-2.6.orig/fs/namespace.c	2009-05-20 15:07:46.000000000 +0200
+++ linux-2.6/fs/namespace.c	2009-05-20 15:10:05.000000000 +0200
@@ -32,6 +32,7 @@
 #include <asm/unistd.h>
 #include "pnode.h"
 #include "internal.h"
+#include "union.h"
 
 #define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head))
 #define HASH_SIZE (1UL << HASH_SHIFT)
@@ -1456,6 +1457,10 @@ static int do_change_type(struct path *p
 	if (path->dentry != path->mnt->mnt_root)
 		return -EINVAL;
 
+	/* Don't change the type of union mounts */
+	if (IS_MNT_UNION(path->mnt))
+		return -EINVAL;
+
 	down_write(&namespace_sem);
 	if (type == MS_SHARED) {
 		err = invent_group_ids(mnt, recurse);
@@ -1477,7 +1482,7 @@ static int do_change_type(struct path *p
  * do loopback mount.
  */
 static int do_loopback(struct path *path, char *old_name,
-				int recurse)
+				int recurse, int mnt_flags)
 {
 	struct path old_path;
 	struct vfsmount *mnt = NULL;
@@ -1507,6 +1512,9 @@ static int do_loopback(struct path *path
 	if (!mnt)
 		goto out;
 
+	if (mnt_flags & MNT_UNION)
+		mnt->mnt_flags |= MNT_UNION;
+
 	err = graft_tree(mnt, path);
 	if (err) {
 		LIST_HEAD(umount_list);
@@ -1600,6 +1608,13 @@ static int do_move_mount(struct path *pa
 	if (err)
 		return err;
 
+	/* moving to or from a union mount is not supported */
+	err = -EINVAL;
+	if (IS_MNT_UNION(path->mnt))
+		goto exit;
+	if (IS_MNT_UNION(old_path.mnt))
+		goto exit;
+
 	down_write(&namespace_sem);
 	while (d_mountpoint(path->dentry) &&
 	       follow_down(&path->mnt, &path->dentry))
@@ -1657,6 +1672,7 @@ out:
 	up_write(&namespace_sem);
 	if (!err)
 		path_put(&parent_path);
+exit:
 	path_put(&old_path);
 	return err;
 }
@@ -1974,7 +1990,7 @@ long do_mount(char *dev_name, char *dir_
 		retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
 				    data_page);
 	else if (flags & MS_BIND)
-		retval = do_loopback(&path, dev_name, flags & MS_REC);
+		retval = do_loopback(&path, dev_name, flags & MS_REC, mnt_flags);
 	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
 		retval = do_change_type(&path, flags);
 	else if (flags & MS_MOVE)

--
--
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