xfs: fix dentry aliasing issues in open_by_handle

Open by handle just grabs an inode by handle and then creates itself
a dentry for it.  While this works for regular files it is horribly
broken for directories, where the VFS locking relies on the fact that
there is only just one single dentry for a given inode, and that
these are always connected to the root of the filesystem so that
it's locking algorithms work (see Documentations/filesystems/Locking)

Remove all the existing open by handle code and replace it with a small
wrapper around the exportfs code which deals with all these issues.
At the same time we also make the checks for a valid handle strict
enough to reject all not perfectly well formed handles - given that
we never hand out others that's okay and simplifies the code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/fs/xfs/linux-2.6/xfs_ioctl.h b/fs/xfs/linux-2.6/xfs_ioctl.h
index 8c16bf2d7e03..7bd7c6afc1eb 100644
--- a/fs/xfs/linux-2.6/xfs_ioctl.h
+++ b/fs/xfs/linux-2.6/xfs_ioctl.h
@@ -34,16 +34,13 @@ xfs_find_handle(
 
 extern int
 xfs_open_by_handle(
-        xfs_mount_t             *mp,
-        xfs_fsop_handlereq_t    *hreq,
         struct file             *parfilp,
-        struct inode            *parinode);
+        xfs_fsop_handlereq_t    *hreq);
 
 extern int
 xfs_readlink_by_handle(
-        xfs_mount_t             *mp,
-        xfs_fsop_handlereq_t    *hreq,
-        struct inode            *parinode);
+        struct file             *parfilp,
+        xfs_fsop_handlereq_t    *hreq);
 
 extern int
 xfs_attrmulti_attr_get(
@@ -67,6 +64,12 @@ xfs_attrmulti_attr_remove(
         char                    *name,
         __uint32_t              flags);
 
+extern struct dentry *
+xfs_handle_to_dentry(
+        struct file             *parfilp,
+        void __user             *uhandle,
+        u32                     hlen);
+
 extern long
 xfs_file_ioctl(
         struct file             *filp,