[issue30438] tarfile would fail to extract tarballs with files under R/O directories (twice)

[Lars Gustäbel]

Lars Gustäbel added the comment:

Actually, it is not prohibited to add the same file to the same archive more 
than once.

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nosy: +lars.gustaebel

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories (twice)

[Catherine Devlin]

Catherine Devlin added the comment:

My last commit to the PR includes a fix by delaying setting permission to all 
files, not just to directories, in .extractall().

It might be better to catch the problem during .add instead, preventing tarring 
multiple copies, but I found subtle difficulties with that approach.  (Do we 
have a foolproof way to establish that a second addition is a duplicate?  What 
if the filename and path is the same, but the file has been changed since last 
time it was added to the tar?)
 
This solution uses code that's already present.

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories (twice)

[Catherine Devlin]

Catherine Devlin added the comment:

Okay, the problem is a little more specific than my last message suggested, but 
also a little less specific than the original report.

A "PermissionError: [Errno 13] Permission denied" is thrown when expanding a 
tarfile to which a file had been added more than once, *if* the file is not 
writeable.  (tarfile expands the file twice, but the second time finds a 
non-writeable file in the way.)

This was true for Yaroslav's case because his file was added once as its 
directory was added, and again when the file was added directly.  The 
permission of the parent directory does not matter after all.

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories (twice)

[Catherine Devlin]

Changes by Catherine Devlin :


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pull_requests: +1892

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories (twice)

[Yaroslav Halchenko]

Changes by Yaroslav Halchenko :


--
title: tarfile would fail to extract tarballs with files under R/O directories 
-> tarfile would fail to extract tarballs with files under R/O directories 
(twice)

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories

[Yaroslav Halchenko]

Yaroslav Halchenko added the comment:

Dear Catherine,

Thank you very much for looking into it!! And sorry that I have missed the fact 
of recursive addition when pointing to a directory.  Indeed though, tar handles 
that case a bit more gracefully.

BUT I feel somewhat dumb since I am afraid that may be the actual original 
issue I have observed was simply because I already had that archive extracted 
and tried to extract it twice, overriding existing files.  That leads to the 
failure I think I was trying to chase down (example with a sample tiny real 
annex repo):

$> wget -q http://onerussian.com/tmp/sample.tar ; python -c 'import tarfile; 
tarfile.open("sample.tar").extractall()'
$> python -c 'import tarfile; tarfile.open("sample.tar").extractall()'
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/lib/python2.7/tarfile.py", line 2081, in extractall
self.extract(tarinfo, path)
  File "/usr/lib/python2.7/tarfile.py", line 2118, in extract
self._extract_member(tarinfo, os.path.join(path, tarinfo.name))
  File "/usr/lib/python2.7/tarfile.py", line 2194, in _extract_member
self.makefile(tarinfo, targetpath)
  File "/usr/lib/python2.7/tarfile.py", line 2234, in makefile
with bltn_open(targetpath, "wb") as target:
IOError: [Errno 13] Permission denied: 
'./sample/.git/annex/objects/G6/qW/SHA256E-s4--181210f8f9c779c26da1d9b2075bde0127302ee0e3fca38c9a83f5b1dd8e5d3b/SHA256E-s4--181210f8f9c779c26da1d9b2075bde0127302ee0e3fca38c9a83f5b1dd8e5d3b'

$> tar -xf sample.tar && echo "extracted ok"
extracted ok


But I wouldn't even consider it a failure but would take it as a feature in my 
case (stuff is read-only for a reason!)

Altogether, I do not have the earth-shaking problem now, thus if you feel that 
issue needs retitle or closing, feel free to do so

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories

[Catherine Devlin]

Catherine Devlin added the comment:

I apologize, I retract my earlier comment - I believe both Yaroslav and I were 
confused about the nature of the problem.  I think it's not related to 
permissions at all, but to adding a file to the tarfile twice.

To see this, use `tarfilero.py` as provided by Yaroslav, but comment out the 
`tar.add('sample/rodir/file')` line (line 16) and run it - everything works 
normally, and the `rodir/file` is present.

It appears that adding the directory to the tarfile also adds the file within 
the directory, and adding the file individually creates a second reference to 
the file.  When expanding, `tarfile` attempts to create the file twice, and the 
second attempt fails because a file by that name already exists.

I still think this is a bug - perhaps re-adding a file already present in a 
tarfile should throw an error, or silently do nothing without adding a second 
reference to the file, or at least the error message when trying to expand a 
file into a path that is blocked by a file already present should give a more 
informative error.  I will look for existing tickets along those lines.

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories

[Catherine Devlin]

Changes by Catherine Devlin :


Removed file: http://bugs.python.org/file46890/issue_30438_test.patch

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories

[Catherine Devlin]

Catherine Devlin added the comment:

I confirmed the error, and that doing the corresponding tar/untar cycle with 
the command-line `tar` utility succeeds.

issue_30438_test.patch adds a unittest version of Yaroslav's demo file to 
test_tarfile.py.  (It's irrelevant if the PR is merged.)

This doesn't actually include a fix.  Issue should remain open.

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keywords: +patch
nosy: +Catherine.Devlin
pull_requests: +1850
Added file: http://bugs.python.org/file46890/issue_30438_test.patch

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[issue30438] tarfile would fail to extract tarballs with files under R/O directories

[Yaroslav Halchenko]

New submission from Yaroslav Halchenko:

If tarfile contains a file under a directory which has no write permission, 
extractall would fail since chmod'ing of the directory is done right when it is 
"extracted".

Please find attached a quick script to demonstrate the problem using 
Python code.  The issue is not just of an academic interest -- git-annex uses 
read-only permission to safe-guard against manual deletion of content. So 
tarball of any of git-annex repository carrying content for at least a single 
file, would not be extractable using Python's tarfile module (works fine with 
pure tar, verified that it is still failing to extract with Python 
v3.6.1-228-g1398b1bc7d from http://github.com/python/cpython).

--
components: IO
files: tarfilero.py
messages: 294217
nosy: Yaroslav.Halchenko
priority: normal
severity: normal
status: open
title: tarfile would fail to extract tarballs with files under R/O directories
versions: Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 3.6
Added file: http://bugs.python.org/file46888/tarfilero.py

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