Memory leak in tmux pane title formatting

[Dan Watkins]

[Impact]

When using powerline with tmux (on bionic), I am experiencing a memory leak that fills my VPS's 1GB of memory in a few days. To avoid memory exhaustion, I have to restart tmux (and therefore anything running in tmux).

[Test Case]

```
lxc launch ubuntu:b reproducer
lxc exec reproducer /bin/bash

# within container
apt update
apt install powerline
tmux

# within tmux
powerline-config tmux setup
```

Without the patch, I see resident set size (per ps) start at ~3MB and after ~30 minutes of tmux uptime it's up to ~4.5MB.

(With the patch, I see no increase in RSS over the same time period.)

[Regression Potential]

This patch affects the format expansion code path, which is used in multiple different ways in the tmux code base. These could all potentially be affected by this change.

[Dan Watkins (oddbloke)]

I have built a tmux package with an upstream patch[0] applied and this has addressed the issue. I am currently trying to create a more minimal reproducer to make this easier to verify as an SRU'able fix.

[0] https://github.com/tmux/tmux/commit/ab6f0bb3485f6626bad6f585e4d17059fe4f7152

[Dan Watkins (oddbloke)]

OK, I've created the SRU template now I've found an easy reproducer.

The upstream commit was first included in 2.7, so anything after bionic should already contain the fix. A rough examination of upstream's git history suggests the memory leak was introduced in tmux 2.4, which is younger than xenial. So I think bionic is the only affected release here.

[Dan Watkins (oddbloke)]

I've pushed up a git commit with the fix and changelog entry to https://code.launchpad.net/~daniel-thewatkins/ubuntu/+source/tmux/+git/tmux/+ref/ubuntu/bionic-devel

[Dan Watkins (oddbloke)]

Andreas pointed out a couple of issues with my git commits (thanks!) so I've re-pushed to https://code.launchpad.net/~daniel-thewatkins/ubuntu/+source/tmux/+git/tmux/+ref/lp1835439

[Brian Murray (brian-murray)]

Hello Dan, or anyone else affected,

Accepted tmux into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/tmux/2.6-3ubuntu0.2 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 and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. 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.

[Dan Watkins (oddbloke)]

I have used the reproduction instructions to confirm that the patched tmux no longer exhibits the same memory leaking behaviour.

Specifically, I launched two containers: one for the -proposed fix and one as a control. After ~10 minutes of uptime, the non-patched tmux has grown from 2948kB RSS to 3864kb RSS whereas the patched tmux has grown from 2920kB to 2948kB.

Marking this as verification-done.

[Łukasz Zemczak (sil2100)]

The verification of the Stable Release Update for tmux has completed successfully and the package has now been 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.

[Launchpad Janitor (janitor)]

This bug was fixed in the package tmux - 2.6-3ubuntu0.2

---------------
tmux (2.6-3ubuntu0.2) bionic; urgency=medium

  * d/p/tmux-format_expand-leak.patch: Do not leak memory when working out job
    name in formats. (LP: #1835439)
  * Update maintainer to reflect Ubuntu delta.

 -- Daniel Watkins <email address hidden> Thu, 04 Jul 2019 15:45:07 -0400