[Impact]
* This bug results in a leak of TLS session objects in the stunnel4 server whenever a connection is closed. For a long running stunnel4 server, it can eventually consume all available memory.
* This bug was introduced in stunnel 5.27, and subsequently fixed in 5.33. Ubuntu Xenial uses 5.30.
* For Ubuntu, only Xenial is currently impacted by this bug, as previous versions of Ubuntu use an older version of stunnel4 (prior to 5.27), and later versions of Ubuntu use a newer version of stunnel4 (at least 5.33).
* This patch backports a single specific fix to free TLS session objects when a connection is closed, but contains no other changes from newer stunnel4 versions.
[Test Case]
* The bug and fix can be reproduced fairly easily by setting up an stunnel4 server, then using openssl s_client to hammer against the stunnel4 server. For example, with the server running on localhost port 443, proxying to a local Apache instance, and using a client certificate:
=
#!/bin/bash
while true; do
echo "" | openssl s_client -connect localhost:443 \
-cert /etc/stunnel/client.pem
done
=
In another window, monitor RSS of the stunnel4 server process with something like:
=
watch 'ps -p $(</var/run/stunnel4/pid) -o rss,comm'
=
* The RSS of the stunnel4 process will continue to grow over time.
* After installing the patched version via my PPA[1] and re-running the test, the RSS of the stunnel4 process will grow for a few minutes and then reach a steady state where it no longer continues to grow.
[1] https://launchpad.net/~lscotte/+archive/ubuntu/stunnel4
[Regression Potential]
* None expected. This backports a fix in newer versions of upstream stunnel4.
* In my own environment, I've been running a production stunnel4 server with my patch for over 85 days (zero restarts of the stunnel4 process). With the current Xenial version I was unable to run for more than 1 day without restarting stunnel4.
[Original Description]
We are running a long-running stunnel4 daemon to proxy TLS connections to another set of servers. After leaving it running for a few weeks, its memory usage had grown to 1.5GB. Restarting it reduced its memory usage to expected levels (VSZ and RSS) but while I've been watching it today it has grown by more than 10MB.
The stunnel website indicates that there have been fixes relating to memory leaks in versions 5.32 and 5.33, but Ubuntu LTS is still running 5.30.
ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: stunnel4 3:5.30-1
ProcVersionSignature: Ubuntu 4.4.0-45.66-generic 4.4.21
Uname: Linux 4.4.0-45-generic i686
ApportVersion: 2.20.1-0ubuntu2.4
Architecture: i386
Date: Mon Jan 9 16:03:37 2017
InstallationDate: Installed on 2015-10-31 (435 days ago)
InstallationMedia: Ubuntu-Server 15.10 "Wily Werewolf" - Release i386 (20151021)
ProcEnviron:
TERM=xterm
SHELL=/bin/bash
PATH=(custom, no user)
LANG=en_US.UTF-8
XDG_RUNTIME_DIR=<set>
SourcePackage: stunnel4
UpgradeStatus: Upgraded to xenial on 2016-05-18 (236 days ago)
mtime.conffile..etc.default.stunnel4: 2016-10-26T22:22:28.166247
Status changed to 'Confirmed' because the bug affects multiple users.