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eace09e63e
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>
(cherry picked from commit
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| .. | ||
| clinic | ||
| stringlib | ||
| abstract.c | ||
| accu.c | ||
| boolobject.c | ||
| bytearrayobject.c | ||
| bytes_methods.c | ||
| bytesobject.c | ||
| call.c | ||
| capsule.c | ||
| cellobject.c | ||
| classobject.c | ||
| codeobject.c | ||
| complexobject.c | ||
| descrobject.c | ||
| dict-common.h | ||
| dictnotes.txt | ||
| dictobject.c | ||
| enumobject.c | ||
| exceptions.c | ||
| fileobject.c | ||
| floatobject.c | ||
| frameobject.c | ||
| funcobject.c | ||
| genericaliasobject.c | ||
| genobject.c | ||
| interpreteridobject.c | ||
| iterobject.c | ||
| listobject.c | ||
| listsort.txt | ||
| lnotab_notes.txt | ||
| longobject.c | ||
| memoryobject.c | ||
| methodobject.c | ||
| moduleobject.c | ||
| namespaceobject.c | ||
| object.c | ||
| obmalloc.c | ||
| odictobject.c | ||
| picklebufobject.c | ||
| rangeobject.c | ||
| README | ||
| setobject.c | ||
| sliceobject.c | ||
| structseq.c | ||
| tupleobject.c | ||
| typeobject.c | ||
| typeslots.inc | ||
| typeslots.py | ||
| unicodectype.c | ||
| unicodeobject.c | ||
| unicodetype_db.h | ||
| unionobject.c | ||
| weakrefobject.c | ||
Source files for various builtin objects