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[3.6] bpo-33015: Fix UB in pthread PyThread_start_new_thread (GH-6008) #10822

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Merged
vstinner merged 1 commit into from
Nov 30, 2018
Merged

[3.6] bpo-33015: Fix UB in pthread PyThread_start_new_thread (GH-6008) #10822

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Build/2018-08-24-09-48-25.bpo-33015.s21y74.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix an undefined behaviour in the pthread implementation of
:c:func:`PyThread_start_new_thread`: add a function wrapper to always return
``NULL``.
40 changes: 36 additions & 4 deletions Python/thread_pthread.h
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,28 @@ PyThread__init_thread(void)
* Thread support.
*/

/* bpo-33015: pythread_callback struct and pythread_wrapper() cast
"void func(void *)" to "void* func(void *)": always return NULL.

PyThread_start_new_thread() uses "void func(void *)" type, whereas
pthread_create() requires a void* return value. */
typedef struct {
void (*func) (void *);
void *arg;
} pythread_callback;

static void *
pythread_wrapper(void *arg)
{
/* copy func and func_arg and free the temporary structure */
pythread_callback *callback = arg;
void (*func)(void *) = callback->func;
void *func_arg = callback->arg;
PyMem_RawFree(arg);

func(func_arg);
return NULL;
}

long
PyThread_start_new_thread(void (*func)(void *), void *arg)
Expand Down Expand Up @@ -218,21 +240,31 @@ PyThread_start_new_thread(void (*func)(void *), void *arg)
pthread_attr_setscope(&attrs, PTHREAD_SCOPE_SYSTEM);
#endif

pythread_callback *callback = PyMem_RawMalloc(sizeof(pythread_callback));

if (callback == NULL) {
return -1;
}

callback->func = func;
callback->arg = arg;

status = pthread_create(&th,
#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
&attrs,
#else
(pthread_attr_t*)NULL,
#endif
(void* (*)(void *))func,
(void *)arg
);
pythread_wrapper, callback);

#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
pthread_attr_destroy(&attrs);
#endif
if (status != 0)

if (status != 0) {
PyMem_RawFree(callback);
return -1;
}

pthread_detach(th);

Expand Down