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When a file on ext4 is stored as sparse the data belonging to zero-filled blocks is not written to storage and the extent map is missing entries for these blocks. Such case can happen both for depth 0 extents (leafs) as well as higher-level tables. Consider a scenario of a file which has a zero-filled beginning (e.g. ISO image). In such case real data starts at block 8. If such a file is stored using 2-level extent structure the extent list in the inode will be depth 1 and will have an entry to a depth 0 (leaf) extent header for blocks 8-n. Unfortunately existing GRUB2 ext2 driver is only able to handle missing entries in leaf extent tables, for which the grub_ext2_read_block() function returns 0. In case the whole leaf extent list is missing for a block the function fails with "invalid extent" error. The fix for this problem relies on the grub_ext4_find_leaf() helper function to distinguish two error cases: missing extent and error walking through the extent tree. The existing error message is raised only for the latter case, while for the missing leaf extent zero is returned from grub_ext2_read_block() indicating a sparse block. Signed-off-by: Krzysztof Nowicki <krzysztof.nowicki@nokia.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'