[Bug 2060666] Re: [SRU] Memory leak in krb5 version 1.17

[Lucas Kanashiro]

Hi Ponnuvel,

I see you prepared a debdiff to fix this issue, if you are seeking for a
sponsor for you package you could use the Patch Pilot program [1]. Long
story short, you could subscribe ~ubuntu-sponsors to this bug and it
would go to the Patch Pilot queue.

This is in the Server team queue, and once we have time we will take a
look if no one else had already done that. It may take some time.

[1] https://ubuntu.com/community/contribute/ubuntu-development/ubuntu-
patch-pilots

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https://bugs.launchpad.net/bugs/2060666

Title:
  [SRU] Memory leak in krb5 version 1.17

Status in krb5 package in Ubuntu:
  Fix Released
Status in krb5 source package in Focal:
  In Progress

Bug description:
  [ Impact ]

  Commit https://github.com/krb5/krb5/commit/1cd2821c19b2b95e39d5fc2f451a035585a40fa5
  altered the memory management of krb5_gss_inquire_cred(), introducing defcred to act as
  an owner pointer when the function must acquire a default credential.
  The commit neglected to update the code to release the default cred
  along the successful path. The old code does not trigger because
  cred_handle is now reassigned, so the default credential is leaked.

  Resulting gradual increase in memory usage (memory leak) and eventual
  crash.

  [ Test Plan ]

  Setup 3 VMs:

  1. Windows Server act as Domain controller (AD)
  2. Windows machine AD Joined with Ostress installed. (Ostress is part of RML utilities https://learn.microsoft.com/en-us/troubleshoot/sql/tools/replay-markup-language-utility)
  3. SQL on Linux AD Joined ( configuration steps https://learn.microsoft.com/en-us/sql/linux/sql-server-linux-ad-auth-adutil-tutorial?view=sql-server-ver16)

  On the Machine with OStress create a file (name it disconnect.ini)
  with the following content under the same folder “C:\Program
  Files\Microsoft Corporation\RMLUtils” where OStress is installed.

  disconnect.ini
  ==============

  [Connection Options]
  LoginTimeout=30
  QuotedIdentifier=Off
  AutocommitMode=On
  DisconnectPct=100.0
  MaxThreadErrors=0

  [Query Options]
  NoSQLBindCol=Off
  NoResultDisplay=Off
  PrepareExecute=Off
  ExecuteAsync=Off
  RollbackOnCancel=Off
  QueryTimeout=0
  QueryDelay=0
  MaxRetries=0
  BatchDisconnectPct=0.0
  CancelPct=0.00
  CancelDelay=0
  CancelDelayMin=0
  CursorType=
  CursorConcurrency=
  RowFetchDelay=0

  [Replay Options]
  Sequencing Options=global sequence
  ::Sequencing Options=global sequence, dtc replay
  DTC Timeout=
  DTC Machine=(local)
  Playback Coordinator=(local)
  StartSeqNum=
  StopSeqNum=
  TimeoutFactor=1.0

  Run the following command to start the load using Ostress, change
  Server name (-S) accordingly and the number of threads (-n) as needed.

  Start 4 different CMD consoles and use the following different commands for each CMD window:
  1. ostress.exe -E -S<ServerName/port> -Q"select * from sys.all_objects" -q -cdisconnect.ini -n40 -r9999999 -oc:\temp\log01 -T146
  2. ostress.exe -E -S<ServerName/port> -Q"select * from sys.all_views" -q -cdisconnect.ini -n40 -r9999999 -oc:\temp\log02 -T146
  3. ostress.exe -E -S<ServerName/port> -Q"select * from sys.all_columns" -q -cdisconnect.ini -n40 -r9999999 -oc:\temp\log03 -T146
  4. ostress.exe -E -S<ServerName/port> -Q"select * from sys.all_parameters" -q -cdisconnect.ini -n40 -r9999999 -oc:\temp\log04 -T146

  After a run of about 5 hours, the memory usage for this is expected to be around 5G with the fix.
  Without the fix, it was observed that it reached around ~22G in 5 hours. Hence the increase in 
  memory usage can be observed if the ostress.exe programs are let to run longer.

  [ Where problems could occur ]

   The fix may not fix the memory leak or could result in releasing the memory
   early in a different code path, and thus resulting in crashes.
   
   A mitigating fact is that the fix has been in Ubuntu since at least 22.04 and
   they do not exhibit any issues.
   
   Likewise I've previously provided the fix in a PPA https://launchpad.net/~pponnuvel/+archive/ubuntu/krb5-focal
   to user who's been hit by this issue. They've tested and confirmed it fixes the memory leak.
   
  [ Other Info ]

  The commit
  https://github.com/krb5/krb5/commit/098f874f3b50dd2c46c0a574677324b5f6f3a1a8
  fixes the leak.

  The fix has been included in newer krb5 releases (Jammy, and Noble
  have the releases with the fix).

  Bionic doesn't have the commit the introduced the memory leak in the first place.
  So this will be a Focal-only backport.

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