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libfdisk: Space before first partition may not be aligned 

libfdisk chooses a grain of 1MB fairly arbitrarily, and this granule
may not be honored by other utilities. GPT disks formatted elsewhere
may have space before the first partition, AND a partition that exists
solely below 1MB. If this occurs, cfdisk ends up adding a free space
region where end < start, resulting in a 16 Exabyte free region.

That's too many exabytes.

This happens because the start gets rounded up to the granule size in
new_freespace() but the end is left alone. The logs show it best:

23274: libfdisk:      CXT: [0x572d878]: initialized:  last=34, grain=2048
23274: libfdisk:      CXT: [0x572d878]: partno=10, start=64
23274: libfdisk:      CXT: [0x572d878]: freespace analyze: partno=10, start=64, end=64
23274: libfdisk:      CXT: [0x572d878]: LBA           34 aligned-up           2048 [grain=2048s]
23274: libfdisk:      CXT: [0x572d878]: LBA           63 aligned-down            0 [grain=2048s]
23274: libfdisk:      CXT: [0x572d878]: LBA           34 aligned-near            0 [grain=2048s]
23274: libfdisk:      CXT: [0x572d878]: 0 in range <2048..0> aligned to 2048
23274: libfdisk:     PART: [0x574bb98]: alloc
23274: libfdisk:      TAB: [0x5749d58]: adding freespace
23274: libfdisk:      TAB: [0x5749d58]: insert entry 0x574bb98 pre=0x574a820 [start=2048, end=63, size=18446744073709549632, freespace  ]

Avoid this by aligning the last value like new_freespace() does.

Signed-off-by: Evan Green <evangreen86@gmail.com>
This commit is contained in:
Evan Green 2019-11-12 14:17:37 -08:00
parent 9cca1ef2d5
commit ae1e82e0b5
1 changed files with 5 additions and 3 deletions
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8
libfdisk/src/table.c
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@ -624,10 +624,12 @@ int fdisk_get_freespaces(struct fdisk_context *cxt, struct fdisk_table **tb)
(uintmax_t) fdisk_partition_get_end(pa)));
/* We ignore small free spaces (smaller than grain) to keep partitions
* aligned, the exception is space before the first partition where
* we assume that cxt->first_lba is aligned. */
* aligned, the exception is space before the first partition when
* cxt->first_lba is aligned. */
if (last + grain < pa->start
|| (last < pa->start && nparts == 0)) {
|| (nparts == 0 &&
(fdisk_align_lba(cxt, last, FDISK_ALIGN_UP) <
pa->start))) {
rc = table_add_freespace(cxt, *tb,
last + (nparts == 0 ? 0 : 1),
pa->start - 1, NULL);