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bpo-40049: Check if symlink exists when extracting from tarfile #19187

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bpo-40049: Check if symlink exists when extracting from tarfile #19187

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999d277
Check if symlink exists before creating
jonnyhsu Mar 27, 2020
905b6c7
Add news entry for bpo-40049
jonnyhsu Mar 28, 2020
083f85e
Add unit test for bpo-40049
jonnyhsu Jun 6, 2020
5eb7e21
Update Misc/NEWS.d/next/Library/2020-03-27-20-49-32.bpo-40049.8079ca.rst
jonnyhsu Jun 6, 2020
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2 changes: 2 additions & 0 deletions Lib/tarfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2232,6 +2232,8 @@ def makelink(self, tarinfo, targetpath):
try:
# For systems that support symbolic and hard links.
if tarinfo.issym():
if os.path.lexists(targetpath):
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Perhaps include a short comment here explaining why this is needed? Something along the lines of "tar should overwrite existing files with symlinks, but os.symlink raises an exception rather than overwriting."

os.unlink(targetpath)
os.symlink(tarinfo.linkname, targetpath)
else:
# See extract().
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12 changes: 12 additions & 0 deletions Lib/test/test_tarfile.py
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Expand Up @@ -755,6 +755,18 @@ def test_compare_members(self):
finally:
tar1.close()

@support.skip_unless_symlink
def test_symlink_overwrite(self):
# Test for issue #40049: Extracting a symlink over an existing file
# in stream mode causes a backwards seek
sympath = os.path.join(TEMPDIR, 'symtype2')
pathlib.Path(sympath).touch()
try:
self.tar.extract('symtype2', TEMPDIR)
self.assertTrue(os.path.islink(sympath))
finally:
pathlib.Path(sympath).unlink(missing_ok=True)

class GzipStreamReadTest(GzipTest, StreamReadTest):
pass

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2020-03-27-20-49-32.bpo-40049.8079ca.rst
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@@ -0,0 +1,3 @@
The :mod:`tarfile` module now checks for an existing symlink before creating a
new one during extraction. This prevents premature scanning of the
archive and errors when extracting from a stream.