Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

[3.11] GH-99729: Unlink frames before clearing them #100047

Merged
merged 4 commits into from
Dec 6, 2022
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
42 changes: 42 additions & 0 deletions Lib/test/test_frame.py
Original file line number Diff line number Diff line change
Expand Up @@ -2,11 +2,13 @@
import re
import sys
import textwrap
import threading
import types
import unittest
import weakref

from test import support
from test.support import threading_helper
from test.support.script_helper import assert_python_ok


Expand Down Expand Up @@ -325,6 +327,46 @@ def f():
if old_enabled:
gc.enable()

@support.cpython_only
@threading_helper.requires_working_threading()
def test_sneaky_frame_object_teardown(self):

class SneakyDel:
def __del__(self):
"""
Stash a reference to the entire stack for walking later.

It may look crazy, but you'd be surprised how common this is
when using a test runner (like pytest). The typical recipe is:
ResourceWarning + -Werror + a custom sys.unraisablehook.
"""
nonlocal sneaky_frame_object
sneaky_frame_object = sys._getframe()

class SneakyThread(threading.Thread):
"""
A separate thread isn't needed to make this code crash, but it does
make crashes more consistent, since it means sneaky_frame_object is
backed by freed memory after the thread completes!
"""

def run(self):
"""Run SneakyDel.__del__ as this frame is popped."""
ref = SneakyDel()

sneaky_frame_object = None
t = SneakyThread()
t.start()
t.join()
# sneaky_frame_object can be anything, really, but it's crucial that
# SneakyThread.run's frame isn't anywhere on the stack while it's being
# torn down:
self.assertIsNotNone(sneaky_frame_object)
while sneaky_frame_object is not None:
self.assertIsNot(
sneaky_frame_object.f_code, SneakyThread.run.__code__
)
sneaky_frame_object = sneaky_frame_object.f_back

if __name__ == "__main__":
unittest.main()
Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix an issue that could cause frames to be visible to Python code as they
are being torn down, possibly leading to memory corruption or hard crashes
of the interpreter.
18 changes: 8 additions & 10 deletions Python/ceval.c
Original file line number Diff line number Diff line change
Expand Up @@ -1617,14 +1617,6 @@ trace_function_exit(PyThreadState *tstate, _PyInterpreterFrame *frame, PyObject
return 0;
}

static _PyInterpreterFrame *
pop_frame(PyThreadState *tstate, _PyInterpreterFrame *frame)
{
_PyInterpreterFrame *prev_frame = frame->previous;
_PyEvalFrameClearAndPop(tstate, frame);
return prev_frame;
}

/* It is only between the PRECALL instruction and the following CALL,
* that this has any meaning.
*/
Expand Down Expand Up @@ -2441,7 +2433,10 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
DTRACE_FUNCTION_EXIT();
_Py_LeaveRecursiveCallTstate(tstate);
if (!frame->is_entry) {
frame = cframe.current_frame = pop_frame(tstate, frame);
// GH-99729: We need to unlink the frame *before* clearing it:
_PyInterpreterFrame *dying = frame;
frame = cframe.current_frame = dying->previous;
_PyEvalFrameClearAndPop(tstate, dying);
_PyFrame_StackPush(frame, retval);
goto resume_frame;
}
Expand Down Expand Up @@ -5833,7 +5828,10 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
assert(tstate->cframe->current_frame == frame->previous);
return NULL;
}
frame = cframe.current_frame = pop_frame(tstate, frame);
// GH-99729: We need to unlink the frame *before* clearing it:
_PyInterpreterFrame *dying = frame;
frame = cframe.current_frame = dying->previous;
_PyEvalFrameClearAndPop(tstate, dying);

resume_with_error:
SET_LOCALS_FROM_FRAME();
Expand Down
3 changes: 3 additions & 0 deletions Python/frame.c
Original file line number Diff line number Diff line change
Expand Up @@ -123,6 +123,9 @@ _PyFrame_Clear(_PyInterpreterFrame *frame)
* to have cleared the enclosing generator, if any. */
assert(frame->owner != FRAME_OWNED_BY_GENERATOR ||
_PyFrame_GetGenerator(frame)->gi_frame_state == FRAME_CLEARED);
// GH-99729: Clearing this frame can expose the stack (via finalizers). It's
// crucial that this frame has been unlinked, and is no longer visible:
assert(_PyThreadState_GET()->cframe->current_frame != frame);
if (frame->frame_obj) {
PyFrameObject *f = frame->frame_obj;
frame->frame_obj = NULL;
Expand Down