[Bug 1899621] Re: [Ubuntu 20.04] zlib: inflateSyncPoint() returns an incorrect result on z15

[Brian Murray]

Hello bugproxy, or anyone else affected,

Accepted zlib into focal-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/zlib/1:1.2.11.dfsg-
2ubuntu1.2 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, what testing has been
performed on the package and change the tag from verification-needed-
focal to verification-done-focal. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-focal. 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.

** Changed in: zlib (Ubuntu Focal)
       Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-focal

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https://bugs.launchpad.net/bugs/1899621

Title:
  [Ubuntu 20.04] zlib: inflateSyncPoint() returns an incorrect result on
  z15

Status in Ubuntu on IBM z Systems:
  In Progress
Status in zlib package in Ubuntu:
  Fix Released
Status in zlib source package in Focal:
  Fix Committed
Status in zlib source package in Groovy:
  Fix Released

Bug description:
  Description:   zlib: inflateSyncPoint() returns an incorrect result on z15
  Symptom:       Certain rsync builds fail with "error in rsync protocol data
                 stream" on z15.
  Problem:       inflateSyncPoint() does not take into account the hardware
                 compression state and returns an incorrect result.
  Solution:      Make inflateSyncPoint() fail if the hardware compression is on.
                 The hardware does not provide enough information in order to
                 implement this function.

  [Impact]

   * Certain rsync builds fail with "error in rsync protocol data
  stream" on z15.

   * On ubuntu, rsync normally uses zstd or lz4. But when rsync is
  forced to use non-default zlib compression (-z flag) it uses
  inflateSyncPoint() API. This can also happen when rsync on the the
  other end doesn't support zstd & lz4.

   * inflateSyncPoint() does not take into account the hardware
  compression state and returns an incorrect result.

   * Make inflateSyncPoint() fail if the hardware compression is on. The
  hardware does not provide enough information in order to implement
  this function.

   * Above makes rsync to succeed, when zlib uses hardware compression.

  [Test Case]

  Reproduction:  z15 only: printf 1 >1 && rsync -z 1 2

  [Regression Potential]

   * inflateSyncPoint API is rarely used. Scanning codesearch, there is
  a lot of false positives due to embedded copies of zlib in all the
  things. I do see that both rsync and backuppc-rsync use it. It used
  during a safety check to ensure that algorithm is not at a sync point
  (or that cannot be determined). Nonetheless, returning error is a
  safer implementation for this API call.

  [Other Info]

   * This is a regression introduced by adding & enabling zlib hw
  acceleration by default on z15; and discovering using rsync that one
  API is implemented incorrectly.

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