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bpo-23325: Fix SIG_IGN and SIG_DFL int comparison in signal module #31759

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Merged
miss-islington merged 4 commits into from
Mar 8, 2022
Merged

bpo-23325: Fix SIG_IGN and SIG_DFL int comparison in signal module #31759

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fdd38cb
bpo-23325: Fix SIG_IGN and SIG_DFL int comparison in signal module
tiran Mar 8, 2022
3438104
Fix comparison in PyErr_SetInterruptEx()
tiran Mar 8, 2022
cc4df05
Compare handler in a safe helper function
tiran Mar 8, 2022
76e3135
Use right order of arguments
tiran Mar 8, 2022
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2022-03-08-11-34-06.bpo-23325.3VQnfo.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
The :mod:`signal` module no longer assumes that :const:`~signal.SIG_IGN` and
:const:`~signal.SIG_DFL` are small int singletons.
44 changes: 35 additions & 9 deletions Modules/signalmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -496,6 +496,7 @@ signal_signal_impl(PyObject *module, int signalnum, PyObject *handler)
_signal_module_state *modstate = get_signal_state(module);
PyObject *old_handler;
void (*func)(int);
int match = 0; // cannot use func == NULL as sentinel, SIG_DFL == 0
#ifdef MS_WINDOWS
/* Validate that signalnum is one of the allowable signals */
switch (signalnum) {
Expand Down Expand Up @@ -528,21 +529,38 @@ signal_signal_impl(PyObject *module, int signalnum, PyObject *handler)
"signal number out of range");
return NULL;
}
if (handler == modstate->ignore_handler) {
func = SIG_IGN;
if (PyCallable_Check(handler)) {
func = signal_handler;
match = 1;
}
else if (handler == modstate->default_handler) {
func = SIG_DFL;
if (!match) {
int cmp = PyObject_RichCompareBool(handler, modstate->ignore_handler, Py_EQ);
switch (cmp) {
case -1:
return NULL;
case 1:
func = SIG_IGN;
match = 1;
break;
}
}
else if (!PyCallable_Check(handler)) {
if (!match) {
int cmp = PyObject_RichCompareBool(handler, modstate->default_handler, Py_EQ);
switch (cmp) {
case -1:
return NULL;
case 1:
func = SIG_DFL;
match = 1;
break;
}
}
if (!match) {
_PyErr_SetString(tstate, PyExc_TypeError,
"signal handler must be signal.SIG_IGN, "
"signal.SIG_DFL, or a callable object");
return NULL;
}
else {
func = signal_handler;
}

/* Check for pending signals before changing signal handler */
if (_PyErr_CheckSignalsTstate(tstate)) {
Expand Down Expand Up @@ -1893,7 +1911,15 @@ PyErr_SetInterruptEx(int signum)

signal_state_t *state = &signal_global_state;
PyObject *func = get_handler(signum);
if (func != state->ignore_handler && func != state->default_handler) {
int is_ign = PyObject_RichCompareBool(func, state->ignore_handler, Py_EQ);
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@serhiy-storchaka serhiy-storchaka Mar 8, 2022

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Is it okay to call a Python code in PyErr_SetInterruptEx()?

If func is a custom callable, it can have an __eq__ method which can call an arbitrary Python code here.

It may be safer to use PyLong_Check() + PyLong_GetLongAndOverflow().

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@tiran tiran Mar 8, 2022

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Good point!

I took a different approach and added a helper function. We can safely assume that the internal handler objects are always exact longs. Comparison between exact longs should never fail.

if (is_ign == -1) {
return -1;
}
int is_dfl = PyObject_RichCompareBool(func, state->default_handler, Py_EQ);
if (is_dfl == -1) {
return -1;
}
if ((is_ign == 0) && (is_dfl == 0)) {
trip_signal(signum);
}
return 0;
Expand Down