[Bug 1965076] [NEW] rsync --update incorrectly reports file "is newer" than itself

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Nick Rosbrook (enr0n):

[Impact]

This bug causes rsync 3.2.3 to wrongly report files with an exact same mtime as being "newer"
implying they would need to be transfered/sync'ed where in fact they are "uptodate".

This breaks users' scripts depending on "is newer" to signal that files need to be sync'ed
when in fact, they don't need to be.

[Test Plan]

Steps to reproduce:

1. Create a local file:
$ touch foo

2. Check if rsync would transfer it using the --update option:
$ rsync -avv --update foo .


If the regression is present, "foo is newer" would be reported:

```
sending incremental file list
delta-transmission disabled for local transfer or --whole-file
foo is newer
total: matches=0  hash_hits=0  false_alarms=0 data=0

sent 61 bytes  received 96 bytes  314.00 bytes/sec
total size is 0  speedup is 0.00
```

If the updated package is installed (from -proposed), "foo is uptodate"
should be reported:

```
sending incremental file list
delta-transmission disabled for local transfer or --whole-file
foo is uptodate
total: matches=0  hash_hits=0  false_alarms=0 data=0

sent 60 bytes  received 106 bytes  332.00 bytes/sec
total size is 0  speedup is 0.00
```

[Regression potential]

The patch changes the behavior of --update so if something goes wrong, it could break backup/sync
jobs. To mitiate that, manual testing of rsync with and without the --update option was done
in addition to the quick [Test Plan] outlined above.

Please note the patch restores the behavior from before version 3.2.3 and has been integrated by upstream
in September 2021. It also is in Kinetic where no visible regression was observed.


[Original description]

rsync 3.2.3 has a broken "--update" option.    See the examples below.
The "--update" option incorrectly makes rsync say a file is newer than itself.
Remove the "--update" option, and rsync correctly says the file is "uptodate".
The right output should of course be "is uptodate" in all cases.
This bug also shows up between machines if the source rsync is 3.1.3 and the destination is 3.2.3.
The bug does not show up if the source rsync is 3.2.3 and the destination is 3.1.3.
The bug was fixed upstream in June 2020:  https://github.com/WayneD/rsync/issues/98

$ touch foo
$ rsync --update --info=skip foo foo
foo is newer                <=== THIS IS NOT CORRECT - A file can't be newer than itself.

Obviously a file should not be listed as newer than itself.  Another
way:

$ touch foo
$ rsync -avv --update foo .
delta-transmission disabled for local transfer or --whole-file
foo is newer                 <=== THIS IS NOT CORRECT - A file can't be newer than itself.
total: matches=0  hash_hits=0  false_alarms=0 data=0
sent 38 bytes  received 96 bytes  268.00 bytes/sec
total size is 0  speedup is 0.00

$ rsync -avv foo .
delta-transmission disabled for local transfer or --whole-file
foo is uptodate              <=== THIS IS CORRECT
total: matches=0  hash_hits=0  false_alarms=0 data=0
sent 41 bytes  received 106 bytes  294.00 bytes/sec
total size is 0  speedup is 0.00

ProblemType: Bug
DistroRelease: Ubuntu 21.10
Package: rsync 3.2.3-4ubuntu1
ProcVersionSignature: Ubuntu 5.13.0-35.40-generic 5.13.19
Uname: Linux 5.13.0-35-generic x86_64
ApportVersion: 2.20.11-0ubuntu71
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Tue Mar 15 22:47:44 2022
InstallationDate: Installed on 2022-03-16 (0 days ago)
InstallationMedia: Ubuntu 21.10 "Impish Indri" - Release amd64 (20211012)
SourcePackage: rsync
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: rsync
     Importance: Unknown
         Status: Fix Released

** Affects: rsync (Ubuntu)
     Importance: Low
         Status: Fix Released

** Affects: rsync (Ubuntu Jammy)
     Importance: Low
         Status: Triaged


** Tags: amd64 apport-bug impish wayland-session
-- 
rsync --update incorrectly reports file "is newer" than itself
https://bugs.launchpad.net/bugs/1965076
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