This is a bug in upstream grub2 code, as follows: In short, it's failing to read the start of a partition that begins on a sector that is not a multiple of 8, and the fallback code is buggy.
In kern/disk.c's grub_disk_read function, an attempt is made to pull the requested sector out of the cache. For any partition type (eg. ext2) which wants a sector within the first 8 of the partition, but not the first, a disk->dev->read call is made below the comment "/* Otherwise read data from the disk actually. */" for the relevant grub-cache-block-sized block (4096 bytes, 8 sectors). This fails under Linux for partitions that do not start on multiples of 8 for the first sectors of the partition because grub (in util/hostdisk.c's open_device) want to read from the partition device, not the disk device, when reading a partition's data (for caching reasons according to the comment) The fallback code (if the if-test of the above-mentioned read call) then attempts to read just the desired sector or sectors, but when it then attempts to grub_memcpy the result into the input buffer (directly before the comment "/* Call the read hook, if any. */" it copies from too far into the resulting buffer. The fix is to remove "+ pos" from this grub_memcpy, and the previous setting of num (between grub_errno = GRUB_ERR_NONE; and p = grub_realloc). (The num setting causes it to read more sectors than necessary, but is otherwise harmless.) That's lines 444 and 461 of http://bzr.debian.org/loggerhead/pkg-grub/trunk/grub/annotate/head:/kern/disk.c revision 1967. pos is the byte offset of the desired sector within the cache-block, and at this point in the code path we are no longer within a cache-block, so adding pos is incorrect. http://bzr.debian.org/loggerhead/pkg-grub/trunk/grub/revision/1855.8.227 is the change that I think introduced this bug, although presumably it was trying to fix another bug... I can't see a bug in the upstream tracker for this. This doesn't affect grub during boot, only when running under Linux (as this fallback path should only be taken in those circumstances) -- Paul "TBBle" Hampson, paul.hamp...@pobox.com -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
