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gh-95778: CVE-2020-10735: Prevent DoS by very large int() (#96499)

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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.
This commit is contained in:
Gregory P. Smith 2022-09-02 09:35:08 -07:00 • committed by GitHub
parent 656167db81
commit 511ca94520
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GPG key ID: 4AEE18F83AFDEB23
28 changed files with 803 additions and 20 deletions
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46
Python/sysmodule.c
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@ -20,6 +20,7 @@ Data members:
#include "pycore_code.h" // _Py_QuickenedCount
#include "pycore_frame.h" // _PyInterpreterFrame
#include "pycore_initconfig.h" // _PyStatus_EXCEPTION()
#include "pycore_long.h" // _PY_LONG_MAX_STR_DIGITS_THRESHOLD
#include "pycore_namespace.h" // _PyNamespace_New()
#include "pycore_object.h" // _PyObject_IS_GC()
#include "pycore_pathconfig.h" // _PyPathConfig_ComputeSysPath0()
@ -1671,6 +1672,45 @@ sys_mdebug_impl(PyObject *module, int flag)
}
#endif /* USE_MALLOPT */
/*[clinic input]
sys.get_int_max_str_digits
Set the maximum string digits limit for non-binary int<->str conversions.
[clinic start generated code]*/
static PyObject *
sys_get_int_max_str_digits_impl(PyObject *module)
/*[clinic end generated code: output=0042f5e8ae0e8631 input=8dab13e2023e60d5]*/
{
PyInterpreterState *interp = _PyInterpreterState_GET();
return PyLong_FromSsize_t(interp->int_max_str_digits);
}
/*[clinic input]
sys.set_int_max_str_digits
maxdigits: int
Set the maximum string digits limit for non-binary int<->str conversions.
[clinic start generated code]*/
static PyObject *
sys_set_int_max_str_digits_impl(PyObject *module, int maxdigits)
/*[clinic end generated code: output=734d4c2511f2a56d input=d7e3f325db6910c5]*/
{
PyThreadState *tstate = _PyThreadState_GET();
if ((!maxdigits) || (maxdigits >= _PY_LONG_MAX_STR_DIGITS_THRESHOLD)) {
tstate->interp->int_max_str_digits = maxdigits;
Py_RETURN_NONE;
} else {
PyErr_Format(
PyExc_ValueError, "maxdigits must be 0 or larger than %d",
_PY_LONG_MAX_STR_DIGITS_THRESHOLD);
return NULL;
}
}
size_t
_PySys_GetSizeOf(PyObject *o)
{
@ -2186,6 +2226,8 @@ static PyMethodDef sys_methods[] = {
SYS_DEACTIVATE_STACK_TRAMPOLINE_METHODDEF
SYS_IS_STACK_TRAMPOLINE_ACTIVE_METHODDEF
SYS_UNRAISABLEHOOK_METHODDEF
SYS_GET_INT_MAX_STR_DIGITS_METHODDEF
SYS_SET_INT_MAX_STR_DIGITS_METHODDEF
#ifdef Py_STATS
SYS__STATS_ON_METHODDEF
SYS__STATS_OFF_METHODDEF
@ -2686,6 +2728,7 @@ static PyStructSequence_Field flags_fields[] = {
{"utf8_mode", "-X utf8"},
{"warn_default_encoding", "-X warn_default_encoding"},
{"safe_path", "-P"},
{"int_max_str_digits", "-X int_max_str_digits"},
{0}
};
@ -2693,7 +2736,7 @@ static PyStructSequence_Desc flags_desc = {
"sys.flags", /* name */
flags__doc__, /* doc */
flags_fields, /* fields */
17
18
};
static int
@ -2734,6 +2777,7 @@ set_flags_from_config(PyInterpreterState *interp, PyObject *flags)
SetFlag(preconfig->utf8_mode);
SetFlag(config->warn_default_encoding);
SetFlagObj(PyBool_FromLong(config->safe_path));
SetFlag(_Py_global_config_int_max_str_digits);
#undef SetFlagObj
#undef SetFlag
return 0;