[Bug 1925381] Re: rsync conceals file deletions from reporting when --dry-run --remove-source-files are used together

[Paride Legovini]

Hello Bill and thanks for this bug report. I can see the issue you
described here (thanks for the reproducer), however I believe it should
be filed/fixed upstream. Maybe [1] should be expanded to cover --remove-
source-files, as the two issues could be related.

Diverging from upstream (or from Debian) has a long-term maintenance
cost (e.g. rebasing the patch at every release) and can lead to
situations which are difficult to handle well: think of a bug that is
later fixed upstream but in a different way, with user-facing
differences. What to do then, break compatibility with the older Ubuntu
releases, or break compatibility with upstream?

While I agree this is a bug in my opinion it is not worth diverging from
upstream here. I am setting the status of this bug report to Triaged (it
is well understood) but with importance: Wishlist.

Should you disagree with my reasoning please comment back and change the
bug status back to New, we'll look at it again. Thanks!

[1] https://bugzilla.samba.org/show_bug.cgi?id=3844

** Bug watch added: Samba Bugzilla #3844
   https://bugzilla.samba.org/show_bug.cgi?id=3844

** Changed in: rsync (Ubuntu)
       Status: New => Triaged

** Changed in: rsync (Ubuntu)
   Importance: Undecided => Wishlist

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https://bugs.launchpad.net/bugs/1925381

Title:
  rsync conceals file deletions from reporting when --dry-run --remove-
  source-files are used together

Status in rsync package in Ubuntu:
  Triaged

Bug description:
  Rsync has an astonishing and dangerous bug:

  The dry run feature (-n / --dry-run) inhibits reporting of file
  deletions when --remove-source-files is used. This is quite serious.
  People use --dry-run to see if an outcome will work as expected before
  a live run. When the simulated run shows *less* destruction than the
  live run, the consequences can be serious because rsync may
  unexpectedly destroy the only copy(*) of a file.

  Users rely on --dry-run. Although users probably expect --dry-run to
  have limitations, we don't expect destructive operations to be under
  reported. If it were reversed, such that the live run were less
  destructive than the dry run, this wouldn't be as serious.

  Reproducer:

  $ mkdir -p /tmp/src /tmp/dest
  $ printf '%s\n' 'yada yada' > /tmp/src/foo.txt
  $ printf '%s\n' 'yada yada' > /tmp/src/bar.txt
  $ cp /tmp/src/foo.txt /tmp/dest
  $ ls /tmp/src/ /tmp/dest/
  /tmp/dest/:
  foo.txt

  /tmp/src/:
  bar.txt  foo.txt

  $ rsync -na --info=remove1 --remove-source-files --existing src/* dest/
  (no output)

  $ rsync -a --info=remove1 --remove-source-files --existing src/* dest/
  sender removed foo.txt

  $ ls /tmp/src/ /tmp/dest/
  /tmp/dest/:
  foo.txt

  /tmp/src/:
  bar.txt

  (*) note when I say it can destroy the only copy of a file, another
  circumstance is needed: that is, rsync does not do a checksum by
  default.  It checks for identical files based on superficial
  parameters like name and date.  So it's possible that two files match
  in the default superficial comparison but differ in the actual
  content.  Losing a unique file in this scenario is perhaps a rare
  corner case, but this bug should be fixed nonetheless.  In the typical
  case of losing files at the source, there is still a significant
  inconvenience of trying to identify what files to copy back.

  Note this bug is similar but differs in a few ways:
  https://bugzilla.samba.org/show_bug.cgi?id=3844

  I've marked this as a security vulnerability because it causes
  unexpected data loss due to --dry-run creating a false expectation.

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