This problem can be reproduced with a synthetic test case.
Essentially,
1) create a zero-filled disk image with one partition.
2) format it as ext4.
3) insert the nilfs2 magic bytes at the right position.
4) insert the nilfs2 bytes field at the right position.
--
Step 1)
# dd if=/dev/zero of=test.img bs=512 count=$((16 * 2048)) # 16
MiB
# dev=$(losetup --find --show test.img)
# parted $dev --script 'mklabel msdos'
# parted $dev --script "mkpart primary 1s $((16 * 2048 - 1))s"
# parted $dev --script 'unit s' --script 'print'
Model: Loopback device (loopback)
Disk /dev/loop0: 32768s
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:
Number Start End Size Type File system Flags
1 1s 32767s 32767s primary
# hexdump -C $dev
... <partition table until 0x200 (first sector) > ...
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa
|..............U.|
00000200 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
01000000
# printf '\x00\x00\x00\x00\x00\x00\x34\x34' | hexdump -C
00000000 00 00 00 00 00 00 34 34 |......44|
00000008
# partprobe $dev
# part=${dev}p1
Step 2)
# mkfs.ext4 $part
Steps 3 and 4)
From gdb/source:
(gdb) ptype/o struct nilfs_super_block
/* offset | size */ type = struct nilfs_super_block {
...
/* 6 | 2 */ uint16_t s_magic;
/* 8 | 2 */ uint16_t s_bytes;
...
#define NILFS_SB_MAGIC 0x3434
#define NILFS_SB_OFFSET 0x400
#define NILFS_SBB_OFFSET(_sz) ((((_sz) / 0x200) - 8) * 0x200)
Then (magic is 0x3434, bytes is 0x0401 == 1025 in litte endian
-- value targeted at the fix)
# printf '\x00\x00\x00\x00\x00\x00\x34\x34\x01\x04' | dd
of=$part bs=1 count=10 conv=notrunc seek=$(( ( (16 * 2048 - 1) - 8) *
512 ))
# hexdump -C $part
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
00ffee00 00 00 00 00 00 00 34 34 01 04 00 00 00 00 00 00
|......44........|
00ffee10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
00fffe00
Original Package)
# LIBBLKID_DEBUG=all udevadm test-builtin blkid /sys/block/$(basename
$dev)/$(basename $part)
...
9576: libblkid: LOWPROBE: [28] ext4:
9576: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x55744f2daec0
9576: libblkid: LOWPROBE: magic sboff=56, kboff=1
9576: libblkid: LOWPROBE: call probefunc()
9576: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x55744f2daec0
9576: libblkid: PROBE: ext2_sb.compat = 0000003C:00000242:0000007B
9576: libblkid: LOWPROBE: assigning UUID [superblocks]
9576: libblkid: LOWPROBE: assigning VERSION [superblocks]
9576: libblkid: LOWPROBE: assigning TYPE [superblocks]
9576: libblkid: LOWPROBE: assigning USAGE [superblocks]
9576: libblkid: LOWPROBE: <-- leaving probing loop (type=ext4) [SUBLKS
idx=28]
...
9576: libblkid: LOWPROBE: [63] nilfs2:
9576: libblkid: LOWPROBE: call probefunc()
9576: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x55744f2daec0
9576: libblkid: LOWPROBE: reuse buffer: off=16772608 len=4096
pr=0x55744f2daec0
9576: libblkid: LOWPROBE: incorrect checksum for type nilfs2, got
2C077E8F, expected 0
9576: libblkid: LOWPROBE: assigning SBBADCSUM [superblocks]
9576: libblkid: LOWPROBE: nilfs2: primary=0, backup=1, swap=1
9576: libblkid: LOWPROBE: assigning VERSION [superblocks]
9576: libblkid: LOWPROBE: assigning TYPE [superblocks]
9576: libblkid: LOWPROBE: assigning USAGE [superblocks]
9576: libblkid: LOWPROBE: <-- leaving probing loop (type=nilfs2)
[SUBLKS idx=63]
...
9576: libblkid: LOWPROBE: ERROR: superblocks chain: ambivalent result
detected (2 filesystems)!
...
# echo $?
1
Original Package with Debug Print)
9604: libblkid: LOWPROBE: [63] nilfs2:
9604: libblkid: LOWPROBE: call probefunc()
9604: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x55c076c8eec0
9604: libblkid: LOWPROBE: reuse buffer: off=16772608 len=4096
pr=0x55c076c8eec0
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:77 :: entry
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:80 :: not sb or not
magic
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:77 :: entry
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:84 :: is_bak 1
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:85 :: is_wholedisk 0
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:86 :: sb->s_dev_size 0
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:87 :: pr->size
16776704
9604: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:96 :: bytes 1025
9604: libblkid: LOWPROBE: incorrect checksum for type nilfs2, got
2C077E8F, expected 0
9604: libblkid: LOWPROBE: assigning SBBADCSUM [superblocks]
9604: libblkid: LOWPROBE: nilfs2: primary=0, backup=1
9604: libblkid: LOWPROBE: nilfs2: primary=0, backup=1, swap=1
Modified Package)
9691: libblkid: LOWPROBE: [63] nilfs2:
9691: libblkid: LOWPROBE: call probefunc()
9691: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x55c12bac1ec0
9691: libblkid: LOWPROBE: reuse buffer: off=16772608 len=4096
pr=0x55c12bac1ec0
9691: libblkid: LOWPROBE: [64] exfat:
Modified Package with Debug Print)
9632: libblkid: LOWPROBE: [63] nilfs2:
9632: libblkid: LOWPROBE: call probefunc()
9632: libblkid: LOWPROBE: reuse buffer: off=1024 len=1024
pr=0x557da562eec0
9632: libblkid: LOWPROBE: reuse buffer: off=16772608 len=4096
pr=0x557da562eec0
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:78 :: entry
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:81 :: not sb or not
magic
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:78 :: entry
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:85 :: is_bak 1
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:86 :: is_wholedisk 0
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:87 :: sb->s_dev_size 0
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:88 :: pr->size
16776704
9632: libblkid: LOWPROBE: nilfs2: nilfs_valid_sb:100 :: bytes 1025
9632: libblkid: LOWPROBE: nilfs2: primary=0, backup=0
9632: libblkid: LOWPROBE: [64] exfat:
--
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Touch seeded packages, which is subscribed to util-linux in Ubuntu.
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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