openssh bugs - May 2022 - [Bug 3431] New: scp truncates file when copying file over itself

https://bugzilla.mindrot.org/show_bug.cgi?id=3431

            Bug ID: 3431
           Summary: scp truncates file when copying file over itself
           Product: Portable OpenSSH
           Version: v9.0p1
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P5
         Component: scp
          Assignee: unassigned-bugs at mindrot.org
          Reporter: christof.schmitt at us.ibm.com

With the new sftp based scp, using scp to copy a file over
itself, truncates that file:

Steps to Reproduce:

1. echo foo > /tmp/bar
2. scp /tmp/bar $(hostname):/tmp/bar
3. cat /tmp/bar

All data in that file is then lost.

This is a problem for scripts, e.g. cluster automation tools
that rely on the fact that a file /tmp/bar can be copied with
scp to all cluster nodes as /tmp/bar, including the node itself.

Changing this behavior is unexpected, and silently dropping the
data seems to be the worst possibly outcome.

In addition to scripts, admins might also be surprised that
copying files (maybe accidentally) to the same host, leaves those
files corrupted.

Would it be possible to change the behavior in this case?
Either explicitly returning an error, or finding a way
to preserve the data would be a better outcome.

https://lists.mindrot.org/pipermail/openssh-unix-dev/2022-February/040059.html
suggests that possibly the sftp server could use a temp file.

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Christof Schmitt <christof.schmitt at us.ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned-bugs at mindrot.org |dbelyavs at redhat.com

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Dmitry Belyavskiy <dbelyavs at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|dbelyavs at redhat.com         |unassigned-bugs at
mindrot.org

--- Comment #1 from Dmitry Belyavskiy <dbelyavs at redhat.com> ---
Not sure that assignment to an external contributor is a good idea :)

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org,
                   |                            |dtucker at dtucker.net
   Attachment #3594|                            |ok?(dtucker at dtucker.net)
              Flags|                            |

--- Comment #2 from Damien Miller <djm at mindrot.org> ---
Created attachment 3594
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3594&action=edit
don't overwrite files

This fixes it for 'scp foo localhost:foo' and 'scp localhost:foo
foo',
but not 'scp localhost:foo localhost:foo'

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Darren Tucker <dtucker at dtucker.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #3594|ok?(dtucker at dtucker.net)    |ok+
              Flags|                            |

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |3418
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #3 from Damien Miller <djm at mindrot.org> ---
This fix has been committed and will be in OpenSSH 9.1, due in a few
months.

commit 56a0697fe079ff3e1ba30a2d5c26b5e45f7b71f8 (HEAD -> master,
origin/master, origin/HEAD)
Author: djm at openbsd.org <djm at openbsd.org>
Date:   Fri May 13 06:31:50 2022 +0000

    upstream: arrange for scp, when in sftp mode, to not ftruncate(3)
files

    early

    previous behavious of unconditionally truncating the destination
file
    would cause "scp ~/foo localhost:" and "scp localhost:foo
~/" to
    delete all the contents of their destination.

    spotted by solene@ sthen@, also bz3431; ok dtucker@

    OpenBSD-Commit-ID: ca39fdd39e0ec1466b9666f15cbcfddea6aaa179


Referenced Bugs:

https://bugzilla.mindrot.org/show_bug.cgi?id=3418
[Bug 3418] tracking bug for openssh-9.1
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--- Comment #4 from Damien Miller <djm at mindrot.org> ---
Closing bugs from openssh-9.1 release cycle

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #5 from Damien Miller <djm at mindrot.org> ---
OpenSSH 9.3 has been released. Close resolved bugs

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