Attaching the debdiff with the fix. This is waiting on validation from the reported user that the boot problem does not happen anymore -- but has already been validated on the running system to produce the correct/expected behavior (UUID / other values are printed by 'udevadm test-builtin blkdid').
I'll be out the next week, so this should probably be handled by Guilherme Piccoli during this time. ** Description changed: + [Impact] + + * Users / systemd can fail to mount a filesystem by UUID + (e.g., during boot, triggering emergency shell prompt) + if the magic bytes for the nilfs filesystem are written + to the right place in a partition of another filesystem, + (for whatever reason or coincidence). + + * Note this can happen after the filesystem/mount is working + correctly, so a change of behavior/problem can potentially + be noticed when trying to mount the filesystem again, which + can very well be the next time the system boots. + + * This happens because if udev blkid detects more than one + filesystem, it does not print the UUID env vars required + to create the /dev/disk/by-id symlinks and other things. + + * The fix enhances the check for valid nilfs superblock by + specifically checking a value read from disk to be valid/ + within a value range, which addresses this one occurrence + and prevents a lot more. + + [Test Case] + + * Synthetic test case written for this problem on comment #6. + + [Regression Potential] + + * Low. The code is contained in the probe for the nilfs filesystem. + + * This just makes it be more restrictive about the possibly valid + values for a few bytes read from disk (that now need to be within + the acceptable range of valid values) so this only decreases false- + positives, and cannot increase false-negatives of valid filesystems. + + [Original 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. ** Patch added: "lp1842437_util-linux.debdiff" https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/1842437/+attachment/5287043/+files/lp1842437_util-linux.debdiff ** Changed in: util-linux (Ubuntu Xenial) Assignee: Mauricio Faria de Oliveira (mfo) => Guilherme G. Piccoli (gpiccoli) -- You received this bug notification because you are a member of Ubuntu 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: [Impact] * Users / systemd can fail to mount a filesystem by UUID (e.g., during boot, triggering emergency shell prompt) if the magic bytes for the nilfs filesystem are written to the right place in a partition of another filesystem, (for whatever reason or coincidence). * Note this can happen after the filesystem/mount is working correctly, so a change of behavior/problem can potentially be noticed when trying to mount the filesystem again, which can very well be the next time the system boots. * This happens because if udev blkid detects more than one filesystem, it does not print the UUID env vars required to create the /dev/disk/by-id symlinks and other things. * The fix enhances the check for valid nilfs superblock by specifically checking a value read from disk to be valid/ within a value range, which addresses this one occurrence and prevents a lot more. [Test Case] * Synthetic test case written for this problem on comment #6. [Regression Potential] * Low. The code is contained in the probe for the nilfs filesystem. * This just makes it be more restrictive about the possibly valid values for a few bytes read from disk (that now need to be within the acceptable range of valid values) so this only decreases false- positives, and cannot increase false-negatives of valid filesystems. [Original 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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