Here is a fixed up commit description, since there were a number of
typo's in the original.
- Ted
commit 07f47fa2c755c139d26fd9fe2ac652d7cda04491
Author: Theodore Ts'o <tytso@xxxxxxx>
Date: Wed Jan 15 23:29:21 2014 -0500
libext2fs: fix off-by-one bug in ext2fs_extent_insert()
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>
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