zfs mount -a: double free / memory corruption / segfault when mountpoint of dataset is not empty

debdiff for focal reported in attach (built and tested).

debdiff for groovy in attach (all zfs autotests completed correctly).

debdiff for hirsute in attach.

New debdiff for focal on top of 0.8.3-1ubuntu12.7.

This bug was fixed in the package zfs-linux - 0.8.4-1ubuntu16

---------------
zfs-linux (0.8.4-1ubuntu16) hirsute; urgency=medium

  * fix potential user-space double free when running "zfs mount -a"
    (LP: #1902588)
   - 4702-Revert-Let-zfs-mount-all-tolerate-in-progress-mounts.patch

 -- Andrea Righi <email address hidden> Fri, 27 Nov 2020 18:40:01 +0000

Hello Lurf, or anyone else affected,

Accepted zfs-linux into groovy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/zfs-linux/0.8.4-1ubuntu11.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-groovy to verification-done-groovy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-groovy. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Hello Lurf, or anyone else affected,

Accepted zfs-linux into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/zfs-linux/0.8.3-1ubuntu12.6 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Steps used to verify the fix (both in focal and groovy):

$ fallocate -l 8G /home/ubuntu/disk.img
$ sudo zpool create pool /home/ubuntu/disk.img
$ for i in {1..20}; do sudo zfs create pool/ds$i; done
$ sudo zfs unmount pool/ds20
$ sudo zfs mount -a & sudo zfs mount -a &
[1] 1964
[2] 1965
ubuntu@groovy:~$ filesystem 'pool/ds20' is already mounted
cannot mount 'pool/ds20': mountpoint or dataset is busy

[1]- Done sudo zfs mount -a
[2]+ Exit 1 sudo zfs mount -a

With the fix applied we should be able to see the error "mountpoint or dataset is busy", due to the concurrent "zfs mount -a" running. That means the old behavior has been restored, since it's not a problem anymore for systemd (and the applied workaround could cause the segfault).

This commit that introduced the segfault was applied o the 0.8-release branch with https://github.com/openzfs/zfs/commit/95fcb04215015950b3388ba0a6edad8e1b463415 so Focal and Groovy are affected.

That change was never applied to the 0.6.5-release or 0.7-release branches, so Bionic and Xenial aren't affected.

The verification of the Stable Release Update for zfs-linux has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

This bug was fixed in the package zfs-linux - 0.8.4-1ubuntu11.1

---------------
zfs-linux (0.8.4-1ubuntu11.1) groovy; urgency=medium

  [ Didier Roche ]
  [ Jean-Baptiste Lallement ]
  * Generate clone uuid without dd which is flagged as having an executable
    stack. Thanks Usarin Heininga for the patch (LP: #1894329)

  [ Andrea Righi ]
  * fix potential user-space double free when running "zfs mount -a"
    (LP: #1902588)
    - 4702-Revert-Let-zfs-mount-all-tolerate-in-progress-mounts.patch

 -- Colin Ian King <email address hidden> Mon, 30 Nov 2020 19:00:00 +0000

This bug was fixed in the package zfs-linux - 0.8.3-1ubuntu12.6

---------------
zfs-linux (0.8.3-1ubuntu12.6) focal; urgency=medium

  [ Didier Roche ]
  [ Jean-Baptiste Lallement ]
  * Generate clone uuid without dd which is flagged as having an executable
    stack. Thanks Usarin Heininga for the patch (LP: #1894329)

  [ Andrea Righi ]
  * fix potential user-space double free when running "zfs mount -a"
    (LP: #1902588)
    - 4702-Revert-Let-zfs-mount-all-tolerate-in-progress-mounts.patch

 -- Colin Ian King <email address hidden> Mon, 30 Nov 2020 19:00:00 +0000