ebtables: Lock file handling has races

Created a hotfix ebtables (2.0.10.4-3ubuntu2~lp1645324hotfix3) in the following PPA.

https://launchpad.net/~amad/+archive/ubuntu/ericsson/+packages

The hotfix is verified by zsolt-babindai (<email address hidden>).

Attaching the patch here to request the start the SRU process.

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Hi,
thank you for providing a patch for SRU review.

I wanted to let you know that you should also add a SRU Template to not be blocked on that when the SRU Team does the review.

Please see https://wiki.ubuntu.com/StableReleaseUpdates for the details of the process.
You usually copy the template that is on there and modify the placeholders to what applies to your case.

Fixed in Debian in 2.0.10.4-3.3, which is present in Xenial (2.0.10.4-3.4ubuntu1) and on.

Note that also, on quick review of the debdiff, which is a backport of the Debian change, I would suggest a version of '2.0.10.4-3ubuntu1.1' rather than '2.0.10.4-3ubuntu2'.

Attaching the debdiff with the changes requested.

What happens if:

1) ebtables is running at the time of an SRU update? Then a new ebtables would fail to detect the lock of the old ebtables invocation.

2) Existing scripts depend on the location of the ebtables lock?

For the SRU, would it make more sense to not move the lock path, and instead arrange for /var/lib/ebtables to be cleared on boot? Opinions welcome.

Unsubscribing ~ubuntu-sponsors as this is in the queue.

Please add your conclusions to Regression Potential if you'd still like to proceed with this.

Good points racb, I think the startup script should test on "start" the existence of the process and the lock. If process is not running it should remove the lock before starting a new process. Also file should be removed on "stop".

I suggest patching Trusty to remove the lock file on boot, before ebtables has any chance to run, if that's possible. That seems to me to be the minimal fix that would resolve any user impact on Trusty. Using /run is a better way to do that, and in the future we'll do it that way (since Zesty has this fixed) but for a stable release update we prefer the minimal and least disruptive fix over a "correct" one.

Creating a "fix" that only removes the file on boot is not a fix....

I have taken over this issue from Amad and have looked into the code. The file exclusive create approach is a bad substitution for real locking. I have a patch done that I am in the process of building a PPA to test, this uses real locking.

File existence as a lock is bad because if the process dies or is killed it leaves a stale file around blocking any new ebtables instance from running. The approach taken in Zesty is not a real solution either since it just shifts the problem around. If the process is killed or crashes by an un-trappable signal the file will persist until the system is rebooted. Hardly a solution....

My patch creates a real lock on the file that is automatically released on exit or a crash.

> Creating a "fix" that only removes the file on boot is not a fix....

Sure, but if it fixes (and is expected to fix completely) the actual impact to users then it may be the most appropriate for an SRU. We don't fix theoretical bugs in SRUs.

> Sure, but if it fixes (and is expected to fix completely) the actual impact
> to users then it may > be the most appropriate for an SRU. We don't fix
> theoretical bugs in SRUs.

As far as I understand the impact to the user was that a lock file from a previous run prevents ebtables to run again. And then second part was that user tried to reboot and that didn't help either. So a reboot is not the fix part, the fix part is in ebtables to not leave stale locks around...

Use real locking in ebtables (LP: #1645324)
    - Prior use of locking by file exclusive access is inadequate
      because if ebtables crashes or is killed it will leave a
      stale lock file behind which then blocks new ebtables from
      running.

Hi dragan-s,

This fix should be sent upstream for inclusion in the official project.

...Louis

@Dragan,

Thank you for your reasoning in comment 18. This makes sense.

Have you sent the real locking fix upstream please, and has there been any response? I see this in the Trusty queue, but doesn't look like this is fixed in Z+1 yet. I guess that wants updating and uploading as soon as Z+1 opens?

A dep3 "Forwarded" header would be most useful!

As the conclusion in this bug is that better lock handling is needed (not just a path move), I've renamed the bug, and the fix isn't in the development release yet so I changed that back to Triaged.

@Robie-

Hi Robie-

if by Z+1 you mean Zesty, I have attached the patch for zesty and Dan nominated it for zesty but we are waiting for someone with permissions to confirm it.

I also filed a bug with upstream Debian:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=860590

The DEP-3 header is in the diff:

+Description: Use real locking in ebtables
+ Prior use of locking by file exclusive access is inadequate
+ because if ebtables crashes or is killed it will leave a
+ stale lock file behind which then blocks new ebtables from
+ running.
+Author: <email address hidden>
+Bug: https://bugs.launchpad.net/ubuntu/+source/ebtables/+bug/1645324
+---
+This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
+Index: ebtables-2.0.10.4/libebtc.c

Is that what you are looking for?

Thanks

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=860590

Hi,
Zesty+1 meant the following release which is in the meantime known as "Artful".
For the SRU handling [1] in general changes need to go to the current development release first and then SRU'ed back. When you worked on this the last time zesty was just about to be released, but artful not yet open - now it is.

Thanks for linking the Debian bug as well!

Also was there any update/response from upstream one can consider when checking the locking rewrite?

@ChristianEhrhardt & @Robie Basak

I'll be covering Dragan for this bug from now on.

I'm afraid that there is not much development activities in the ebtables upstream project nowadays :

Last 3 ebtables commits :
Date: Tue Mar 28 19:42:39 2017 +0530
Date: Thu Oct 22 16:41:03 2015 +0200
Date: Sat May 16 12:31:58 2015 +0200

I'll try to reach the netfilter team, and see if they are still accepting patches for this project.
In case of the upstream project is "dead", do you think there is a chance Dragan's fix can land in Ubuntu anyway ?

- Eric

Additionally, it seems like it isn't the first time Debian patched ebtables, thus Ubuntu package without submitting upstream.

Example : https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=813760

Zesty :
libebtc.c:137:#define LOCKDIR "/run"
libebtc.c:138:#define LOCKFILE LOCKDIR"/ebtables.lock"

Zesty changelog :
...
  * Non-maintainer upload.
  ...
  * debian/patches/lockdirfix.patch: Move the lock file to /run instead of
    /var/lib/ebtables directory (Closes: #813760)
...
 -- Laurent Bigonville <email address hidden> Fri, 05 Feb 2016 13:29:39 +0100

Xenial :
x/ebtables-2.0.10.4/libebtc.c:137:#define LOCKDIR "/run"
x/ebtables-2.0.10.4/libebtc.c:138:#define LOCKFILE LOCKDIR"/ebtables.lock"

ebtables git repo :

Still point to "/var/lib/ebtables" for LOCKDIR, where debian changed it in 2016 to "/run".

libebtc.c:137:#define LOCKDIR "/var/lib/ebtables"
libebtc.c:138:#define LOCKFILE LOCKDIR"/lock"

From what I see Debian already abandonned to keep the ebtables project maintainer in the loop.

Artful debdiff

ebtables (for IPv4, IPv6, ARP and Ethernet bridging, respectively) are intended to be replaced with nft as a single unified implementation. With that being said, nowadays all the development/focus is happening in nft instead.

- Eric

<slashd> rbasak, morning I see you talked with dragan about this LP: #1645324. From now on, I'm taking care of this bug, I see that some ppls suggest Dragan to submit in the upstream project first, but in this case it seems that ebtables is nearly "dead" last commits were made in 2015. Nowadays, all the development happen in nft. Do you think Dragan's patch could be eligilble for SRu anyway ? considering that Dragan already submitted the same patch to Debian ebtables but not upstream.

<rbasak> slashd: can we get the patch committed/uploaded into Debian? That would also alleviate Ubuntu's maintenance burden.

This bug was fixed in the package ebtables - 2.0.10.4-3.5ubuntu2

---------------
ebtables (2.0.10.4-3.5ubuntu2) artful; urgency=medium

  * Use real locking in ebtables (LP: #1645324)
    - Prior use of locking by file exclusive access is inadequate
      because if ebtables crashes or is killed it will leave a
      stale lock file behind which then blocks new ebtables from
      running.

 -- Dragan Stancevic <email address hidden> Tue, 18 Apr 2017 17:32:38 -0500

Hello Amad, or anyone else affected,

Accepted ebtables into zesty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ebtables/2.0.10.4-3.5ubuntu1.17.04.1 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, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

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

Hello Amad, or anyone else affected,

Accepted ebtables into yakkety-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ebtables/2.0.10.4-3.5ubuntu1.16.10.1 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, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

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

Hello Amad, or anyone else affected,

Accepted ebtables into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ebtables/2.0.10.4-3.4ubuntu2 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 to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

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

Hello Amad, or anyone else affected,

Accepted ebtables into trusty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ebtables/2.0.10.4-3ubuntu1.14.04.1 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, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

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

Hi All,

I have successfully tested the following versions of ebtables

for Trusty: 2.0.10.4-3ubuntu1.14.04.1 OK

for Xenial: 2.0.10.4-3.4ubuntu2 OK

for Yakkety: 2.0.10.4-3.5ubuntu1.16.10.1 OK

for Zesty: 2.0.10.4-3.5ubuntu1.17.04.1 OK

Szilard

@szilard, is your testing/verification has been made based on Dragan's test case #1 and #2 ?

Could you please provide more details ? output ....

This will be useful informations for the SRU members to give their final approval.

- Eric

The verification was done using Test Case 1 and Test Case 2

However I noticed that in the Trusty version the lock file
is located at /var/lib/ebtables/lock
Whereas on the Xenial/Yakkety/Zesty versions lock file is
at /run/ebtables.lock

@szilard,

The constant values (#define LOCKDIR ...) hasn't been touched in these patches, meaning that it was already like that before this SRU.

With that being said, the LOCKDIR location isn't a problem, so IMHO, there is no need for the LOCKDIR in Trusty to move to "/run" if it doesn't create a problem.

The real issue here is that if ebtables crashes or is killed it leave a stale lock file behind which then blocks new ebtables from running.

This SRU is precisely fixing this issue by improving the locking mechanism.

- Eric

It has been brought to my attention the following :

"I was able to install and test it and seems to be OK."

^ Tested by someone affected by the issue using the trusty-proposed package.

This bug was fixed in the package ebtables - 2.0.10.4-3.5ubuntu1.17.04.1

---------------
ebtables (2.0.10.4-3.5ubuntu1.17.04.1) zesty; urgency=medium

  * Use real locking in ebtables (LP: #1645324)
    - Prior use of locking by file exclusive access is inadequate
      because if ebtables crashes or is killed it will leave a
      stale lock file behind which then blocks new ebtables from
      running.

 -- Dragan Stancevic <email address hidden> Tue, 18 Apr 2017 17:32:38 -0500

The verification of the Stable Release Update for ebtables 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.

This bug was fixed in the package ebtables - 2.0.10.4-3.5ubuntu1.16.10.1

---------------
ebtables (2.0.10.4-3.5ubuntu1.16.10.1) yakkety; urgency=medium

  * Use real locking in ebtables (LP: #1645324)
    - Prior use of locking by file exclusive access is inadequate
      because if ebtables crashes or is killed it will leave a
      stale lock file behind which then blocks new ebtables from
      running.

 -- Dragan Stancevic <email address hidden> Tue, 18 Apr 2017 17:32:38 -0500

This bug was fixed in the package ebtables - 2.0.10.4-3.4ubuntu2

---------------
ebtables (2.0.10.4-3.4ubuntu2) xenial; urgency=medium

  * Use real locking in ebtables (LP: #1645324)
    - Prior use of locking by file exclusive access is inadequate
      because if ebtables crashes or is killed it will leave a
      stale lock file behind which then blocks new ebtables from
      running.

 -- Dragan Stancevic <email address hidden> Mon, 29 May 2017 16:07:53 -0400

This bug was fixed in the package ebtables - 2.0.10.4-3ubuntu1.14.04.1

---------------
ebtables (2.0.10.4-3ubuntu1.14.04.1) trusty; urgency=medium

  * Use real locking in ebtables (LP: #1645324)
    - Prior use of locking by file exclusive access is inadequate
      because if ebtables crashes or is killed it will leave a
      stale lock file behind which then blocks new ebtables from
      running.

 -- Dragan Stancevic <email address hidden> Thu, 02 Mar 2017 17:34:55 -0600