[PATCH] Cygwin: Allow to set SO_PEERCRED zero

[Mark Geisert <mark@maxrnd.com>]

The existing code errors as EINVAL any attempt to set a value for
SO_PEERCRED via setsockopt() on an AF_UNIX/AF_LOCAL socket.  But to
enable the workaround set_no_getpeereid behavior for Python one has
to be able to set SO_PEERCRED to zero.  Ergo, this patch.  Python has
no way to specify a NULL pointer for 'optval'.

---
 winsup/cygwin/fhandler_socket_local.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler_socket_local.cc b/winsup/cygwin/fhandler_socket_local.cc
index c94bf828f..421b8bbdb 100644
--- a/winsup/cygwin/fhandler_socket_local.cc
+++ b/winsup/cygwin/fhandler_socket_local.cc
@@ -1430,7 +1430,8 @@ fhandler_socket_local::setsockopt (int level, int optname, const void *optval,
 	     FIXME: In the long run we should find a more generic solution
 	     which doesn't require a blocking handshake in accept/connect
 	     to exchange SO_PEERCRED credentials. */
-	  if (optval || optlen)
+	  /* Temporary: Allow only '(int) 0' to be specified. */
+	  if (optlen < (socklen_t) sizeof (int) || 0 != *(int *) optval)
 	    set_errno (EINVAL);
 	  else
 	    ret = af_local_set_no_getpeereid ();
-- 
2.29.2