[2/4] xfs: prevent swapext from operating on write-only files

[Greg KH <gregkh@suse.de>]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Dan Rosenberg <dan.j.rosenberg@gmail.com>

commit 1817176a86352f65210139d4c794ad2d19fc6b63 upstream.

This patch prevents user "foo" from using the SWAPEXT ioctl to swap
a write-only file owned by user "bar" into a file owned by "foo" and
subsequently reading it.  It does so by checking that the file
descriptors passed to the ioctl are also opened for reading.

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 fs/xfs/xfs_dfrag.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/fs/xfs/xfs_dfrag.c
+++ b/fs/xfs/xfs_dfrag.c
@@ -74,7 +74,9 @@ xfs_swapext(
 		goto out_free_sxp;
 	}
 
-	if (!(file->f_mode & FMODE_WRITE) || (file->f_flags & O_APPEND)) {
+	if (!(file->f_mode & FMODE_WRITE) ||
+	    !(file->f_mode & FMODE_READ) ||
+	    (file->f_flags & O_APPEND)) {
 		error = XFS_ERROR(EBADF);
 		goto out_put_file;
 	}
@@ -86,6 +88,7 @@ xfs_swapext(
 	}
 
 	if (!(target_file->f_mode & FMODE_WRITE) ||
+	    !(target_file->f_mode & FMODE_READ) ||
 	    (target_file->f_flags & O_APPEND)) {
 		error = XFS_ERROR(EBADF);
 		goto out_put_target_file;