Converting a large enough `int` to a decimal string raises `ValueError` as expected. However, the raise comes _after_ the quadratic-time base-conversion algorithm has run to completion. For effective DOS prevention, we need some kind of check before entering the quadratic-time loop. Oops! =)
The quick fix: essentially we catch _most_ values that exceed the threshold up front. Those that slip through will still be on the small side (read: sufficiently fast), and will get caught by the existing check so that the limit remains exact.
The justification for the current check. The C code check is:
```c
max_str_digits / (3 * PyLong_SHIFT) <= (size_a - 11) / 10
```
In GitHub markdown math-speak, writing $M$ for `max_str_digits`, $L$ for `PyLong_SHIFT` and $s$ for `size_a`, that check is:
$$\left\lfloor\frac{M}{3L}\right\rfloor \le \left\lfloor\frac{s - 11}{10}\right\rfloor$$
From this it follows that
$$\frac{M}{3L} < \frac{s-1}{10}$$
hence that
$$\frac{L(s-1)}{M} > \frac{10}{3} > \log_2(10).$$
So
$$2^{L(s-1)} > 10^M.$$
But our input integer $a$ satisfies $|a| \ge 2^{L(s-1)}$, so $|a|$ is larger than $10^M$. This shows that we don't accidentally capture anything _below_ the intended limit in the check.
<!-- gh-issue-number: gh-95778 -->
* Issue: gh-95778
<!-- /gh-issue-number -->
Co-authored-by: Gregory P. Smith [Google LLC] <greg@krypto.org>
Integer to and from text conversions via CPython's bignum `int` type is not safe against denial of service attacks due to malicious input. Very large input strings with hundred thousands of digits can consume several CPU seconds.
This PR comes fresh from a pile of work done in our private PSRT security response team repo.
Signed-off-by: Christian Heimes [Red Hat] <christian@python.org>
Tons-of-polishing-up-by: Gregory P. Smith [Google] <greg@krypto.org>
Reviews via the private PSRT repo via many others (see the NEWS entry in the PR).
<!-- gh-issue-number: gh-95778 -->
* Issue: gh-95778
<!-- /gh-issue-number -->
I wrote up [a one pager for the release managers](https://docs.google.com/document/d/1KjuF_aXlzPUxTK4BMgezGJ2Pn7uevfX7g0_mvgHlL7Y/edit#). Much of that text wound up in the Issue. Backports PRs already exist. See the issue for links.
* gh-96132: Add some comments and minor fixes missed in the original PR
* Update Doc/using/cmdline.rst
Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
⚠️⚠️ Note for reviewers, hackers and fellow systems/low-level/compiler engineers ⚠️⚠️
If you have a lot of experience with this kind of shenanigans and want to improve the **first** version, **please make a PR against my branch** or **reach out by email** or **suggest code changes directly on GitHub**.
If you have any **refinements or optimizations** please, wait until the first version is merged before starting hacking or proposing those so we can keep this PR productive.
- "comparison of integers of different signs" in typeobject.c
- only define static_builtin_index_is_set in DEBUG builds
- only define recreate_gil with ifdef HAVE_FORK
* Treat tp_weakref and tp_dictoffset like other opaque slots for multiple inheritance.
* Document Py_TPFLAGS_MANAGED_DICT and Py_TPFLAGS_MANAGED_WEAKREF in what's new.
- On WASI `ENOTCAPABLE` is now mapped to `PermissionError`.
- The `errno` modules exposes the new error number.
- `getpath.py` now ignores `PermissionError` when it cannot open landmark
files `pybuilddir.txt` and `pyenv.cfg`.
* Make sure that tp_dictoffset is correct with Py_TPFLAGS_MANAGED_DICT is set.
* Avoid traversing managed dict twice when subclassing class with Py_TPFLAGS_MANAGED_DICT set.
We only statically initialize for core code and builtin modules. Extension modules still create
the tuple at runtime. We'll solve that part of interpreter isolation separately.
This change includes generated code. The non-generated changes are in:
* Tools/clinic/clinic.py
* Python/getargs.c
* Include/cpython/modsupport.h
* Makefile.pre.in (re-generate global strings after running clinic)
* very minor tweaks to Modules/_codecsmodule.c and Python/Python-tokenize.c
All other changes are generated code (clinic, global strings).
An unrecognized format character in PyUnicode_FromFormat() and
PyUnicode_FromFormatV() now sets a SystemError.
In previous versions it caused all the rest of the format string to be
copied as-is to the result string, and any extra arguments discarded.
* Add test for inheriting explicit __dict__ and weakref.
* Restore 3.10 behavior for multiple inheritance of C extension classes that store their dictionary at the end of the struct.
* Store tp_weaklist on the interpreter state for static builtin types.
* Factor out _PyStaticType_GET_WEAKREFS_LISTPTR().
* Add _PyStaticType_ClearWeakRefs().
* Add a comment about how _PyStaticType_ClearWeakRefs() loops.
* Document the change.
* Update Doc/whatsnew/3.12.rst
* Fix a typo.
This is the last precursor to storing tp_subclasses (and tp_weaklist) on the interpreter state for static builtin types.
Here we add per-type storage on PyInterpreterState, but only for the static builtin types. This involves the following:
* add PyInterpreterState.types
* move PyInterpreterState.type_cache to it
* add a "num_builtins_initialized" field
* add a "builtins" field (a static array big enough for all the static builtin types)
* add _PyStaticType_GetState() to look up a static builtin type's state
* (temporarily) add PyTypeObject.tp_static_builtin_index (to hold the type's index into PyInterpreterState.types.builtins)
We will be eliminating tp_static_builtin_index in a later change.
* Add _Py_memory_repeat function to pycore_list
* Add _Py_RefcntAdd function to pycore_object
* Use the new functions in tuplerepeat, list_repeat, and list_inplace_repeat
Static builtin types are finalized by calling _PyStaticType_Dealloc(). Before this change, we were skipping finalizing such a type if it still had subtypes (i.e. its tp_subclasses hadn't been cleared yet). The problem is that types hold several heap objects, which leak if we skip the type's finalization. This change addresses that.
For context, there's an old comment (from e9e3eab0b8) that says the following:
// If a type still has subtypes, it cannot be deallocated.
// A subtype can inherit attributes and methods of its parent type,
// and a type must no longer be used once it's deallocated.
However, it isn't clear that is actually still true. Clearing tp_dict should mean it isn't a problem.
Furthermore, the only subtypes that might still be around come from extension modules that didn't clean them up when unloaded (i.e. extensions that do not implement multi-phase initialization, AKA PEP 489). Those objects are already leaking, so this change doesn't change anything in that regard. Instead, this change means more objects gets cleaned up that before.
This is the first of several precursors to storing tp_subclasses (and tp_weaklist) on the interpreter state for static builtin types.
We do the following:
* add `_PyStaticType_InitBuiltin()`
* add `_Py_TPFLAGS_STATIC_BUILTIN`
* set it on all static builtin types in `_PyStaticType_InitBuiltin()`
* shuffle some code around to be able to use _PyStaticType_InitBuiltin()
* rename `_PyStructSequence_InitType()` to `_PyStructSequence_InitBuiltinWithFlags()`
* add `_PyStructSequence_InitBuiltin()`.
Kumar Aditya
Mark Dickinson
Gregory P. Smith
Irit Katriel
Pablo Galindo Salgado
Mark Shannon
Christian Heimes
Brandt Bucher
Matthias Görgens
Ken Jin
Erlend E. Aasland
Eric Snow
Petr Viktorin
Serhiy Storchaka
Tim Gates
Brandt Bucher
Dong-hee Na
Pamela Fox
Aivars Kalvāns
Pieter Eendebak