[Bug 2077487] Re: Broken atime in 2.2.2-0ubuntu9 (noble's version)

Hi Jessica,

You're correct - only the DKMS package itself has the fix to this point,
for those installing via DKMS. Kernels that release with the ZFS module
bundled need to follow. The Noble and Jammy-HWE 6.8 kernels will contain
the updated ZFS module in the upcoming s2024.09.30 kernel cycle,
releasing the week of 11-Nov.


John Cabaj

--
You received this bug notification because you are subscribed to linux
in Ubuntu.
Matching subscriptions: Bgg, Bmail, Nb
https://bugs.launchpad.net/bugs/2077487

Title:
Broken atime in 2.2.2-0ubuntu9 (noble's version)

Status in linux package in Ubuntu:
Invalid
Status in linux-hwe-6.8 package in Ubuntu:
Invalid
Status in zfs-linux package in Ubuntu:
Fix Released
Status in linux source package in Noble:
Confirmed
Status in linux-hwe-6.8 source package in Noble:
Invalid
Status in zfs-linux source package in Noble:
Fix Released

Bug description:
SRU Justification

[Impact]

* 2.2.2-0ubuntu9 has the 6.7 compat series, including https://github.com/openzfs/zfs/commit/db4fc559cc1931b9219e62aa505cd5c51a17b232, but does not include the fix for that commit (affects both pre-6.7 and post-6.7),
https://github.com/openzfs/zfs/commit/f0bf7a247dbb030d68c7fd2b5526dd111cc775d0. This manifests for me on the current (6.8.0-40.40~22.04.3) 22.04 HWE kernel as writes to a file resetting atime back to 0 (reads still seem to work as expected though given that state), which of course breaks real-world things (in my case, I can no longer successfully run LLVM's test suite).

Thanks to CONFIG_INIT_STACK_ALL_ZERO=y being the default it seems like
this isn't a kernel memory disclosure and is instead a deterministic
use of 0, so I don't believe this to be a blatant security
vulnerability. This also explains the behaviour observed above.

This needs fixing in noble, and then propagating back through whatever
kernels are pulling in this version, since linux-modules vendors
copies of the pre-built DKMS modules, with the current 6.8 HWE kernel
using 2.2.2-0ubuntu9 explicitly.

[Fix]

* Include f0bf7a247dbb: "[PATCH] Linux 6.7 compat: zfs_setattr fix
atime update" from upstream ZFS as quilt patch.

[Test Case]

* Build tested against Noble generic
* Ran autopkgktests for regressions, none encountered
* Ran the following test case:

Using zfs-linux 2.2.2-0ubuntu9
$ cd /path/to/zfs
$ rm -f foo
$ touch foo
$ stat foo
$ # observe initial access time of 0 since epoch (1970-01-01)

Using zfs-linux 2.2.2-0ubuntu9.1
$ cd /path/to/zfs
$ rm -f foo
$ touch foo
$ stat foo
$ # observe initial access time same as modify/change/birth

Also see results attached as "zfs-bad" and "zfs-good", respectively

[Where things could go wrong]

* Low chance of regression, isolated instantiation and logic fix.
* Addition of time delta check could cause issues during unexpected delay > 2 seconds.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2077487/+subscriptions