py/mpz: Ignore calls to to_bytes with zero length. #14493
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Calling `int.to_bytes` on integers large enough to let MicroPython switch to mpz for their internal representation, if the length of the requested byte array is zero the code will try to fill a zero-length buffer with sign extension bytes and crash. Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## master #14493 +/- ##
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Coverage 98.39% 98.39%
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Files 161 161
Lines 21204 21205 +1
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+ Hits 20864 20865 +1
Misses 340 340 ☔ View full report in Codecov by Sentry. |
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Code size report: |
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Is |
Yes, it's flaky. I have rerun it. |
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Sorry, this looks like it is already part of #13087 - I was looking for pending PRs that made changes to py/mpz and I missed that one :( |
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@agatti Your patch is a lot smaller, so if the bigger one in 13087 turns out too big then it might be a better pick. 😆 |
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Requesting a zero-sized bytes representation of large integers (using mpz rather than
long long) would attempt to sign-extend a zero-bytes buffer with no bounds checking. This PR sidesteps the whole issue by not performing any operation if the requested length is zero, with the same runtime behaviour as smaller integers in the same situation.For the record, code like
int.from_bytes(bytes(range(20)), "big").to_bytes(0, "big")would crash MicroPython with: