[PATCH] Cygwin: Allow to set SO_PEERCRED zero

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[PATCH] Cygwin: Allow to set SO_PEERCRED zero

Mark Geisert
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

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Re: [PATCH] Cygwin: Allow to set SO_PEERCRED zero

cygwin-patches mailing list
Hi Mark,

On Dec  6 22:28, Mark Geisert wrote:

> 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);

That breaks existing callers calling setsockopt like this:

  setsockopt (fd, SOL_SOCKET, SO_PEERCRED, NULL, 0);

This should stay backward-compatible.  It should allow the above
as well as your int usage, otherwise postfix will stop working.

Also, please write either

  *(int *) optval != 0

or just

  !!*(int *) optval


Thanks,
Corinna