** Changed in: zlib (Ubuntu Focal)
Status: New => In Progress
** Changed in: zlib (Ubuntu Groovy)
Status: New => In Progress
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https://bugs.launchpad.net/bugs/1899621
Title:
[Ubuntu 20.04] zlib: inflateSyncPoint() returns an incorrect result on
z15
Status in Release Notes for Ubuntu:
New
Status in Ubuntu on IBM z Systems:
New
Status in zlib package in Ubuntu:
In Progress
Status in zlib source package in Focal:
In Progress
Status in zlib source package in Groovy:
In Progress
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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