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gh-106092: Fix use-after-free crash in frame_dealloc (#106875) 

It was possible for the trashcan to delay the deallocation of a
PyFrameObject until after its corresponding _PyInterpreterFrame has
already been freed.  So frame_dealloc needs to avoid dereferencing the
f_frame pointer unless it first checks that the pointer still points
to the interpreter frame within the frame object.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
This commit is contained in:
Anders Kaseorg 2023-08-01 02:32:18 -07:00 committed by GitHub
parent 052a0d1106
commit 557b05c7a5
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2 changed files with 9 additions and 6 deletions
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2
Misc/NEWS.d/next/Core and Builtins/2023-07-18-16-13-51.gh-issue-106092.bObgRM.rst Normal file
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@ -0,0 +1,2 @@
Fix a segmentation fault caused by a use-after-free bug in ``frame_dealloc``
when the trashcan delays the deallocation of a ``PyFrameObject``.

13
Objects/frameobject.c
View File

@ -879,9 +879,6 @@ frame_dealloc(PyFrameObject *f)
/* It is the responsibility of the owning generator/coroutine
* to have cleared the generator pointer */
assert(f->f_frame->owner != FRAME_OWNED_BY_GENERATOR ||
_PyFrame_GetGenerator(f->f_frame)->gi_frame_state == FRAME_CLEARED);
if (_PyObject_GC_IS_TRACKED(f)) {
_PyObject_GC_UNTRACK(f);
}
@ -889,10 +886,14 @@ frame_dealloc(PyFrameObject *f)
Py_TRASHCAN_BEGIN(f, frame_dealloc);
PyObject *co = NULL;
/* GH-106092: If f->f_frame was on the stack and we reached the maximum
* nesting depth for deallocations, the trashcan may have delayed this
* deallocation until after f->f_frame is freed. Avoid dereferencing
* f->f_frame unless we know it still points to valid memory. */
_PyInterpreterFrame *frame = (_PyInterpreterFrame *)f->_f_frame_data;
/* Kill all local variables including specials, if we own them */
if (f->f_frame->owner == FRAME_OWNED_BY_FRAME_OBJECT) {
assert(f->f_frame == (_PyInterpreterFrame *)f->_f_frame_data);
_PyInterpreterFrame *frame = (_PyInterpreterFrame *)f->_f_frame_data;
if (f->f_frame == frame && frame->owner == FRAME_OWNED_BY_FRAME_OBJECT) {
/* Don't clear code object until the end */
co = frame->f_executable;
frame->f_executable = NULL;