bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux (#1370)

* bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux

* Add NEWS entry

Lib/test/test_socket.py

@@ -4682,6 +4682,10 @@ class TestUnixDomain(unittest.TestCase):
             else:
                 raise
 
+    def testUnbound(self):
+        # Issue #30205
+        self.assertEqual(self.sock.getsockname(), '')
+
     def testStrAddr(self):
         # Test binding to and retrieving a normal string pathname.
         path = os.path.abspath(support.TESTFN)

Misc/NEWS

@@ -317,6 +317,8 @@ Extension Modules
 Library
 -------
 
+- bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux.
+
 - bpo-30228: The seek() and tell() methods of io.FileIO now set the internal
   seekable attribute to avoid one syscall on open() (in buffered or text mode).
 

Modules/socketmodule.c

@@ -1211,9 +1211,9 @@ makesockaddr(SOCKET_T sockfd, struct sockaddr *addr, size_t addrlen, int proto)
     {
         struct sockaddr_un *a = (struct sockaddr_un *) addr;
 #ifdef __linux__
-        if (a->sun_path[0] == 0) {  /* Linux abstract namespace */
-            addrlen -= offsetof(struct sockaddr_un, sun_path);
-            return PyBytes_FromStringAndSize(a->sun_path, addrlen);
+        size_t linuxaddrlen = addrlen - offsetof(struct sockaddr_un, sun_path);
+        if (linuxaddrlen > 0 && a->sun_path[0] == 0) {  /* Linux abstract namespace */
+            return PyBytes_FromStringAndSize(a->sun_path, linuxaddrlen);
         }
         else
 #endif /* linux */