rsync - Aug 2018 - [Bug 13569] New: --link-dest may follow symlinks and failure to hard link a non-regular file is fatal

https://bugzilla.samba.org/show_bug.cgi?id=13569

            Bug ID: 13569
           Summary: --link-dest may follow symlinks and failure to hard
                    link a non-regular file is fatal
           Product: rsync
           Version: 3.1.3
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P5
         Component: core
          Assignee: wayned at samba.org
          Reporter: buczek+samba-bugzilla at molgen.mpg.de
        QA Contact: rsync-qa at samba.org

Created attachment 14406
  --> https://bugzilla.samba.org/attachment.cgi?id=14406&action=edit
script to demonstrate bug

With --link-dest the search for a candidate to link from, follows symlinks in
directory path components, when the path element is a directory in the source
tree but a symlink in the --link-dest tree. This may trigger unwanted side
effects (e.g. automounter mounts). Moreover, the target candidate found might
not be suitable for a hard link, because it may be on another file system. For
regular files, rsync tried so fall back to copy, which might be unwanted (e.g.
going over nfs). For non-regular files, rsync will create the destination file,
but report an error and exit with a non-zero exit status.

Attachment is a script which demonstrates the bug. Outputs "RSYNC
FAILED" on my
system.

The second rsync of the scripts fails, because src/dir is a link to another
filesystem in the --link-dest tree but a directory in the new src and
src/dir/test is a non-regular file.

Happens with 3.0.9 and with the current git master version.

We've seen our rsync based backup triggering automounts on the backup server
or
fail from time to time, because of the above problem. Users sometimes move
directories somewhere else and create a symlink to the new destination in the
old place or visa versa. So with incremental backups you do have real files one
day and a symlink to the same tree another day.

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