Problem:
- the ext4 filesystem is detected correctly at the beginning of the partition.
- the nilfs2 filesystem is detected incorrectly at the end of the partition.
- the nilfs2 checksum is invalid, but that is ignored by udev builtin blkid.
- the detection of more than one filesystems causes an error and stop blkid.
# LIBBLKID_DEBUG=all udevadm test-builtin blkid /sys/block/loop0/loop0p1
...
30555: libblkid: LOWPROBE: [28] ext4:
30555: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x558f3ea3dec0
30555: libblkid: LOWPROBE: magic sboff=56, kboff=1
30555: libblkid: LOWPROBE: call probefunc()
30555: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x558f3ea3dec0
30555: libblkid: PROBE: ext2_sb.compat = 0000003C:00000246:0000007B
30555: libblkid: LOWPROBE: assigning UUID [superblocks]
30555: libblkid: LOWPROBE: assigning VERSION [superblocks]
30555: libblkid: LOWPROBE: assigning TYPE [superblocks]
30555: libblkid: LOWPROBE: assigning USAGE [superblocks]
...
30555: libblkid: LOWPROBE: [63] nilfs2:
30555: libblkid: LOWPROBE: call probefunc()
30555: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x558f3ea3dec0
30555: libblkid: LOWPROBE: reuse buffer: off=1072689152 len=4096
pr=0x558f3ea3dec0
30555: libblkid: LOWPROBE: incorrect checksum for type nilfs2, got 3F8DC6BA,
expected 2D2D206B
30555: libblkid: LOWPROBE: assigning SBBADCSUM [superblocks]
30555: libblkid: LOWPROBE: nilfs2: primary=0, backup=1, swap=1
30555: libblkid: LOWPROBE: assigning LABEL [superblocks]
30555: libblkid: LOWPROBE: assigning UUID [superblocks]
30555: libblkid: LOWPROBE: assigning VERSION [superblocks]
30555: libblkid: LOWPROBE: assigning TYPE [superblocks]
30555: libblkid: LOWPROBE: assigning USAGE [superblocks]
...
30555: libblkid: LOWPROBE: ERROR: superblocks chain: ambivalent result detected
(2 filesystems)!
...
# echo $?
1
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https://bugs.launchpad.net/bugs/1842437
Title:
Xenial: libblkid: fix false-positive/misdetection of nilfs2 filesystem
with udev
Status in util-linux package in Ubuntu:
Fix Released
Status in util-linux source package in Xenial:
In Progress
Bug description:
The nilfs filesystem has a backup superblock at the end of the device.
If the magic number is coincidentally found at the right position
and the filesystem is on a partition/not-wholedisk device,
the only check left is for checksum verification,
which is explicitly ignored in 'udev built-in blkid'.
This causes blkid to detect one actually valid filesystem with a
superblock at the beginning of the device (e.g., ext4), and then
an invalid nilfs2 filesystem due to a coincidental magic number
at the end of the device.
And this causes blkid to break out of the safeprobe routine
(which expects a single filesystem to be detected), and not
print the UUIDs, thus not creating /dev/disk/by-uuid/ links
which prevent mounting the partition by-uuid at boot time,
causing emergency shell/boot failures.
This upstream fix resolved the problem by introducing a check
for the 'bytes' paramenters in the superblock, which is read
from disk, and turns out to have an out-of-range value.
- 'liblkid: Add length check in probe_nilfs2 before crc32'
https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=ac681a310c32319423297544833932f4d689a7a2
$ git describe --contains ac681a310c32319423297544833932f4d689a7a2
v2.29-rc1~172
Xenial, which is v2.27.1-based, is the only release that needs it.
Bionic is v2.31.1, so all post-Xenial supported releases have it.
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https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/1842437/+subscriptions
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