[3.9] bpo-44493: Add missing terminated NUL in sockaddr_un's length (GH-26866) (GH-32140) (GH-32156)

Add missing terminated NUL in sockaddr_un's length

- Linux: https://man7.org/linux/man-pages/man7/unix.7.html
- *BSD: SUN_LEN
(cherry picked from commit f6b3a07b7df60dc04d0260169ffef6e9796a2124)

Co-authored-by: ty <zonyitoo@users.noreply.github.com>

Automerge-Triggered-By: GH:gpshead
(cherry picked from commit 5944807b09717d43bb017f700e8c451dd07199ed)

Co-authored-by: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>

2 files changed, 9 insertions, 1 deletions

diff --git a/Misc/NEWS.d/next/Library/2021-07-26-10-46-49.bpo-44493.xp3CRH.rst b/Misc/NEWS.d/next/Library/2021-07-26-10-46-49.bpo-44493.xp3CRH.rst
new file mode 100644
index 0000000..390a722
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-07-26-10-46-49.bpo-44493.xp3CRH.rst
@@ -0,0 +1,3 @@
+Add missing terminated NUL in sockaddr_un's length
+
+This was potentially observable when using non-abstract AF_UNIX datagram sockets to processes written in another programming language.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index a22060d..6d6c92e 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -1722,6 +1722,8 @@ getsockaddrarg(PySocketSockObject *s, PyObject *args,
                                 "AF_UNIX path too long");
                 goto unix_out;
             }
+
+            *len_ret = path.len + offsetof(struct sockaddr_un, sun_path);
         }
         else
 #endif /* linux */
@@ -1733,10 +1735,13 @@ getsockaddrarg(PySocketSockObject *s, PyObject *args,
                 goto unix_out;
             }
             addr->sun_path[path.len] = 0;
+
+            /* including the tailing NUL */
+            *len_ret = path.len + offsetof(struct sockaddr_un, sun_path) + 1;
         }
         addr->sun_family = s->sock_family;
         memcpy(addr->sun_path, path.buf, path.len);
-        *len_ret = path.len + offsetof(struct sockaddr_un, sun_path);
+        
         retval = 1;
     unix_out:
         PyBuffer_Release(&path);