socket is missing a null pointer check on PyThread_allocate_lock return value

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

We should just change it to PyMutex now.

@kumaraditya303

@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.

gh-150406: Check result of PyThread_allocate_lock() for netdb_lock (G…

[3.14] gh-150406: Check result of PyThread_allocate_lock() for netdb_…

[3.13] gh-150406: Check result of PyThread_allocate_lock() for netdb_…

[3.15] gh-150406: Check result of PyThread_allocate_lock() for netdb_…

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`socket` is missing a null pointer check on `PyThread_allocate_lock` return value #150406

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Bug description:

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CPython versions tested on:

Operating systems tested on:

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

	#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

socket is missing a null pointer check on PyThread_allocate_lock return value #150406

Description

Bug report

Bug description:

Backports

CPython versions tested on:

Operating systems tested on:

Linked PRs

Activity

kumaraditya303 commented on May 26, 2026

KowalskiThomas commented on May 26, 2026

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`socket` is missing a null pointer check on `PyThread_allocate_lock` return value #150406