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

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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