peter-toth commented on PR #57040:
URL: https://github.com/apache/spark/pull/57040#issuecomment-4907775814
@gaogaotiantian the snippet tests `os.path.realpath`, but the extract loop
uses `os.path.relpath` (to strip the leading `spark-x/` package dir), and
`relpath` *emits* `..` rather than resolving it:
```python
>>> os.path.relpath("spark-x/../../etc/evil", "spark-x/")
'../../etc/evil'
```
So `member.name` still contains `..` when it reaches `tar.extract(member,
dest)` (no `filter`), which writes outside `dest`. Repro:
```python
import io, os, tarfile, tempfile
with tempfile.TemporaryDirectory() as tmp:
dest = os.path.join(tmp, "dest"); os.makedirs(dest)
p = os.path.join(tmp, "m.tar")
with tarfile.open(p, "w") as t:
info = tarfile.TarInfo("spark-x/../evil.txt"); info.size = 5
t.addfile(info, io.BytesIO(b"pwned"))
with tarfile.open(p) as t:
for m in t.getmembers():
m.name = os.path.relpath(m.name, "spark-x" + os.path.sep)
t.extract(m, dest)
print(os.path.exists(os.path.join(tmp, "evil.txt"))) # True -> escaped
dest
```
`realpath` *does* resolve `..` - which is exactly why a
`realpath(os.path.join(dest, name))`-stays-under-`realpath(dest)` check is an
effective, version-independent guard.
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