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[3.14] gh-116008: Detect freed thread state in faulthandler (GH-141988) #142013

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Merged
merged 1 commit into from
Nov 27, 2025
Merged

[3.14] gh-116008: Detect freed thread state in faulthandler (GH-141988) #142013

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21 changes: 21 additions & 0 deletions Include/internal/pycore_pymem.h
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,27 @@ static inline int _PyMem_IsPtrFreed(const void *ptr)
#endif
}

// Similar to _PyMem_IsPtrFreed() but expects an 'unsigned long' instead of a
// pointer.
static inline int _PyMem_IsULongFreed(unsigned long value)
{
#if SIZEOF_LONG == 8
return (value == 0
|| value == (unsigned long)0xCDCDCDCDCDCDCDCD
|| value == (unsigned long)0xDDDDDDDDDDDDDDDD
|| value == (unsigned long)0xFDFDFDFDFDFDFDFD
|| value == (unsigned long)0xFFFFFFFFFFFFFFFF);
#elif SIZEOF_LONG == 4
return (value == 0
|| value == (unsigned long)0xCDCDCDCD
|| value == (unsigned long)0xDDDDDDDD
|| value == (unsigned long)0xFDFDFDFD
|| value == (unsigned long)0xFFFFFFFF);
#else
# error "unknown long size"
#endif
}

extern int _PyMem_GetAllocatorName(
const char *name,
PyMemAllocatorName *allocator);
Expand Down
23 changes: 19 additions & 4 deletions Python/traceback.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1095,6 +1095,9 @@ tstate_is_freed(PyThreadState *tstate)
if (_PyMem_IsPtrFreed(tstate->interp)) {
return 1;
}
if (_PyMem_IsULongFreed(tstate->thread_id)) {
return 1;
}
return 0;
}

Expand All @@ -1114,7 +1117,7 @@ dump_traceback(int fd, PyThreadState *tstate, int write_header)
}

if (tstate_is_freed(tstate)) {
PUTS(fd, " <tstate is freed>\n");
PUTS(fd, " <freed thread state>\n");
return;
}

Expand All @@ -1139,12 +1142,16 @@ dump_traceback(int fd, PyThreadState *tstate, int write_header)
PUTS(fd, " <freed frame>\n");
break;
}
// Read frame->previous early since memory can be freed during
// dump_frame()
_PyInterpreterFrame *previous = frame->previous;

if (dump_frame(fd, frame) < 0) {
PUTS(fd, " <invalid frame>\n");
break;
}

frame = frame->previous;
frame = previous;
if (frame == NULL) {
break;
}
Expand Down Expand Up @@ -1241,7 +1248,9 @@ write_thread_id(int fd, PyThreadState *tstate, int is_current)
tstate->thread_id,
sizeof(unsigned long) * 2);

write_thread_name(fd, tstate);
if (!_PyMem_IsULongFreed(tstate->thread_id)) {
write_thread_name(fd, tstate);
}

PUTS(fd, " (most recent call first):\n");
}
Expand Down Expand Up @@ -1299,7 +1308,6 @@ _Py_DumpTracebackThreads(int fd, PyInterpreterState *interp,
return "unable to get the thread head state";

/* Dump the traceback of each thread */
tstate = PyInterpreterState_ThreadHead(interp);
unsigned int nthreads = 0;
_Py_BEGIN_SUPPRESS_IPH
do
Expand All @@ -1310,11 +1318,18 @@ _Py_DumpTracebackThreads(int fd, PyInterpreterState *interp,
PUTS(fd, "...\n");
break;
}

if (tstate_is_freed(tstate)) {
PUTS(fd, "<freed thread state>\n");
break;
}

write_thread_id(fd, tstate, tstate == current_tstate);
if (tstate == current_tstate && tstate->interp->gc.collecting) {
PUTS(fd, " Garbage-collecting\n");
}
dump_traceback(fd, tstate, 0);

tstate = PyThreadState_Next(tstate);
nthreads++;
} while (tstate != NULL);
Expand Down
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