`socket` is missing a null pointer check on `PyThread_allocate_lock` return value

[KowalskiThomas]

Bug report

Bug description:

In socketmodule.c, a call is made to PyThread_allocate_lock to allocate a lock, but its return value is not checked.

cpython/Modules/socketmodule.c

Lines 9294 to 9296 in a189e3d

	#if defined(USE_GETHOSTBYNAME_LOCK)
	netdb_lock = PyThread_allocate_lock();
	#endif

That same netdb_lock is later used without being checked for null-ness either.

cpython/Modules/socketmodule.c

Lines 6219 to 6237 in a189e3d

	#ifdef USE_GETHOSTBYNAME_LOCK
	PyThread_acquire_lock(netdb_lock, 1);
	#endif
	_Py_COMP_DIAG_PUSH
	_Py_COMP_DIAG_IGNORE_DEPR_DECLS
	h = gethostbyname(name);
	_Py_COMP_DIAG_POP
	#endif /* HAVE_GETHOSTBYNAME_R */
	Py_END_ALLOW_THREADS
	/* Some C libraries would require addr.__ss_family instead of
	addr.ss_family.
	Therefore, we cast the sockaddr_storage into sockaddr to
	access sa_family. */
	sa = SAS2SA(&addr);
	ret = gethost_common(state, h, SAS2SA(&addr), sizeof(addr),
	sa->sa_family);
	#ifdef USE_GETHOSTBYNAME_LOCK
	PyThread_release_lock(netdb_lock);
	#endif

If PyThread_allocate_lock fails (due to being out of memory, that's the only failure case as far as I can tell), this will lead to a crash.

Backports

Once fix, the fix would have to be backported to 3.15 / 3.14 / 3.13 which have the same problem.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other, macOS

Linked PRs

• gh-150406: check result of PyThread_allocate_lock for netdb_lock #150407
• [3.15] gh-150406: Check result of PyThread_allocate_lock() for netdb_lock (GH-150407) #150616
• [3.14] gh-150406: Check result of PyThread_allocate_lock() for netdb_lock (GH-150407) #150617
• [3.13] gh-150406: Check result of PyThread_allocate_lock() for netdb_lock (GH-150407) #150618

[kumaraditya303]

We should just change it to PyMutex now.

[KowalskiThomas]

@kumaraditya303 I created #150452 to track this. I think socket can be changed to use PyMutex on main/future versions of CPython, but the current issue is still relevant for older versions.