Re: [PATCH 14/24] libext2fs: fix bounds check of the bitmap test range in get_free_blocks2

[Theodore Ts'o <tytso@mit.edu>]

On Fri, Jul 18, 2014 at 03:53:59PM -0700, Darrick J. Wong wrote:
> In the loop in ext2fs_get_free_blocks2, we ask the bitmap if there's a
> range of free blocks starting at "b" and ending at "b + num - 1".
> That quantity is the number of the last block in the range.  Since
> ext2fs_blocks_count() returns the number of blocks and not the number
> of the last block in the filesystem, the check is incorrect.
> 
> Put in a shortcut to exit the loop if finish > start, because in that
> case it's obvious that we don't need to reset to the beginning of the
> FS to continue the search for blocks.  This is needed to terminate the
> loop because the broken test meant that b could get large enough to
> equal finish, which would end the while loop.
> 
> The attached testcase shows that with the off by one error, it is
> possible to throw e2fsck into an infinite loop while it tries to
> find space for the inode table even though there's no space for one.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Thanks, applied.

					- Ted