Properly update MBR when installing with saved partitions #378
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GPT::write_protective_mbr_into() only writes the partition table, leaving the MBR boot code alone. Manually zero out the remainder of the MBR to prevent attempted boots via the bootloader we're overwriting. Fixes: 8420896 ("install: on error, just write a GPT") Fixes: ace675b ("download: defer validity using saved partitions rather than zeroes")
In the case of saved partitions, image_copy_default() was writing a merged GPT and copying any data after it, but wasn't copying the MBR. With the previous commit, this would result in a BIOS-unbootable install; before the previous commit, this would result in a BIOS boot using the bootloader previously installed to the disk. Fixes: 66ffb81 ("download: restore saved partitions while writing back first MiB")
If we merge saved partitions, we update the installed GPT to match the size of the target disk; otherwise, we don't. We were not updating the protective MBR to match the target disk size in either case, which is inconsistent. Have merge() update the protective MBR as well.
lucab
approved these changes
Sep 21, 2020
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When installing with saved partitions, we were failing to clear the MBR boot code during install and on error, and failing to write the new boot code afterward. Fixes regressions in #340.
Also update the size of the protective MBR partition after install, for consistency with the GPT.
https://bugzilla.redhat.com/show_bug.cgi?id=1879690