GIT: unionfs2-2.6.27.y: GFS2: rename causes kernel Oops

[Erez Zadok]

commit 6fcefe4aef997caa4bfcd7fd53b850dbe890bb7d
Author: Bob Peterson <rpeterso at redhat.com>
Date:   Wed Jul 14 18:12:26 2010 -0400

    GFS2: rename causes kernel Oops
    
    commit 728a756b8fcd22d80e2dbba8117a8a3aafd3f203 upstream.
    
    This patch fixes a kernel Oops in the GFS2 rename code.
    
    The problem was in the way the gfs2 directory code was trying
    to re-use sentinel directory entries.
    
    In the failing case, gfs2's rename function was renaming a
    file to another name that had the same non-trivial length.
    The file being renamed happened to be the first directory
    entry on the leaf block.
    
    First, the rename code (gfs2_rename in ops_inode.c) found the
    original directory entry and decided it could do its job by
    simply replacing the directory entry with another.  Therefore
    it determined correctly that no block allocations were needed.
    
    Next, the rename code deleted the old directory entry prior to
    replacing it with the new name.  Therefore, the soon-to-be
    replaced directory entry was temporarily made into a directory
    entry "sentinel" or a place holder at the start of a leaf block.
    
    Lastly, it went to re-add the replacement directory entry in
    that leaf block.  However, when gfs2_dirent_find_space was
    looking for space in the leaf block, it used the wrong value
    for the sentinel.  That threw off its calculations so later
    it decides it can't really re-use the sentinel and therefore
    must allocate a new leaf block.  But because it previously decided
    to re-use the directory entry, it didn't waste the time to
    grab a new block allocation for the inode.  Therefore, the
    inode's i_alloc pointer was still NULL and it crashes trying to
    reference it.
    
    In the case of sentinel directory entries, the entire dirent is
    reused, not just the "free space" portion of it, and therefore
    the function gfs2_dirent_find_space should use the value 0
    rather than GFS2_DIRENT_SIZE(0) for the actual dirent size.
    
    Fixing this calculation enables the reproducer programs to work
    properly.
    
    Signed-off-by: Bob Peterson <rpeterso at redhat.com>
    Signed-off-by: Steven Whitehouse <swhiteho at redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>

diff --git a/fs/gfs2/dir.c b/fs/gfs2/dir.c
index eed040d..4c83653 100644
--- a/fs/gfs2/dir.c
+++ b/fs/gfs2/dir.c
@@ -393,7 +393,7 @@ static int gfs2_dirent_find_space(const struct gfs2_dirent *dent,
 	unsigned totlen = be16_to_cpu(dent->de_rec_len);
 
 	if (gfs2_dirent_sentinel(dent))
-		actual = GFS2_DIRENT_SIZE(0);
+		actual = 0;
 	if (totlen - actual >= required)
 		return 1;
 	return 0;