When inserting the first extent into an empty inode, the
ext2fs_extent_insert() leaves path->left set to 1 instead of 0. Since
path->curr is pointing at the last (only) extent in the file,
path->left should be 0.
This is mostly harmless, and gets corrected fairly quickly if the
calling applicaton jumps to a different part of the extent tree ---
for example, by calling ext2fs_extent_goto(), or calling
ext2fs_extent_get with the flags argument set to EXT2_EXTENT_ROOT.
Which is why we hadn't noticed this problem until now.
However, if you insert four extents using ext2fs_extent_insert, the
fourth insert will end up copying too many bytes in the i_block[]
array, since path->left is one larger than it should be. This results
in the inode fields i_generation, i_file_acl, and i_size_high getting
zeroed out.
This problem can be replicated as follows:
% cp /dev/null /tmp/foo.img
% mke2fs -F -t ext4 /tmp/foo.img 100
% debugfs -w /tmp/foo.img
debugfs: write /dev/null foo
debugfs: set_inode_field foo i_size_hi 1
debugfs: stat foo
<----- note that the inode's size is 4294967296
debugfs: extent_open foo
debugfs (extent ino 12): insert --after 0 1 100
debugfs (extent ino 12): insert --after 1 1 101
debugfs (extent ino 12): insert --after 2 1 102
debugfs (extent ino 12): insert --after 3 1 103
debugfs (extent ino 12): extent_close
debugfs: stat foo
<----- note that the inode's size is now 0
debugfs: quit
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
---
lib/ext2fs/extent.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/lib/ext2fs/extent.c b/lib/ext2fs/extent.c
index 5cdc2e4..6f4f1d2 100644
--- a/lib/ext2fs/extent.c
+++ b/lib/ext2fs/extent.c
@@ -1092,8 +1092,10 @@ errcode_t ext2fs_extent_insert(ext2_extent_handle_t handle, int flags,
ix++;
path->left--;
}
- } else
+ } else {
ix = EXT_FIRST_INDEX(eh);
+ path->left = -1;
+ }
path->curr = ix;
--
1.8.5.rc3.362.gdf10213
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
