with debug we could confirm that other fields in the backup superblock are
invalid,
such as the device size, which was not checked for not being a whole-disk
device,
and the bytes length, which is greater than the superblock structure size (8243
vs 1024).
so, the fix to check for the bytes field not being out-of-range resolves
this case.
primary superblock
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:77 :: entry
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:80 :: not sb or not magic
backup superblock
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:77 :: entry
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:84 :: is_bak 1
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:85 :: is_wholedisk 0
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:86 :: sb->s_dev_size
3_472_328_296_366_616_623
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:87 :: pr->size 1_072_693_248
586: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:96 :: bytes 8243
586: libblkid: LOWPROBE: incorrect checksum for type nilfs2, got 56C7A81B,
expected 2D2D206B
586: libblkid: LOWPROBE: assigning SBBADCSUM [superblocks]
586: libblkid: LOWPROBE: nilfs2: primary=0, backup=1
586: libblkid: LOWPROBE: nilfs2: primary=0, backup=1, swap=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.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/1842437/+subscriptions
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