Disable ECKD Thin Provisioning to prevent data loss
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
Ubuntu on IBM z Systems |
Fix Released
|
High
|
Unassigned | ||
linux (Ubuntu) |
Invalid
|
Undecided
|
Skipper Bug Screeners | ||
Eoan |
Fix Released
|
Undecided
|
Unassigned |
Bug Description
SRU Justification:
------------------
[Impact]
* A severe problem with 'thin provisioning ECKD volumes', introduced with 19.10's kernel 5.3, was identified.
* For enhanced space efficient (ese) volumes, errors may occur when accessing not formatted tracks.
* In such a case the driver either formats the track on the fly for write requests or returns zero data for read requests.
* But if a write request spans multiple tracks, the indication of an unformatted track can be in wc applied to all tracks.
* Hence tracks containing data will be handled as empty tracks, resulting in zero data being returned on read, or overwriting
existing data with zero on write.
[Fix]
[Test Case]
* An s390x LPAR with Eoan / kernel 5.3 and at least one 3390 DASD (ECKD) disk is needed ('discard' enabled, which is default).
* Writing arbitrary files (but with known content, e.g. all '1's) to fill the disk up to a certain level
* Since all 3390 DASDs (mod-3, 9, 27 or 54 ...) have 56,664 bytes per track, writing a file (again with simple but known content) with a size of a multiple of 56,664 bytes on a thin provisioned ECKD DASD device should provoke the error situation.
* Check the files for any modifications (partially filled with '0', cut/truncated, deleted/zero length).
[Regression Potential]
* The regression potential is moderate since this is purely s390x specific,
* limited to thin provisioned DASD disks on Eoan / kernel 5.3
* and just disables the broken feature and reverts things back to a DASD functionality that is known to work.
[Other Info]
* For 19.10 / Eoan no real fix will be provided, but a patch for disabling this feature completely (this bug/patch).
* The broken functionality that got introduced in Eoan, got already partially removed due to problems on z/VM.
* For 20.04 / Focal a proper fix is in the works that will be made available as backport to Focal's kernel 5.4.
CVE References
tags: | added: architecture-s39064 bugnameltc-183399 severity-high targetmilestone-inin1910 |
Changed in ubuntu: | |
assignee: | nobody → Skipper Bug Screeners (skipper-screen-team) |
affects: | ubuntu → linux (Ubuntu) |
Changed in ubuntu-z-systems: | |
importance: | Undecided → High |
summary: |
- [UBUNTU] - Disable Thin Provisioning to prevent data loss + Disable ECKD Thin Provisioning to prevent data loss |
Changed in linux (Ubuntu Eoan): | |
status: | Triaged → In Progress |
Changed in linux (Ubuntu Eoan): | |
status: | In Progress → Fix Committed |
Changed in ubuntu-z-systems: | |
status: | In Progress → Fix Committed |
Changed in ubuntu-z-systems: | |
status: | Fix Committed → Fix Released |
------- Comment From <email address hidden> 2020-01-22 08:25 EDT------- /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/1830731
IBM has discovered a problem with a new feature within Ubuntu 19.10
with following feature request which might result in data loss.,
https:/
For 19.10 we will not provide a fix for it, but a patch for disabling this feature.
For 20.04 a fix will be made available via backport from kernel 5.6 where the patch is targeted for.
Info will follow