* pinfo.h (winpids::pid_access): New element.

(winpids::winpids): Rejigger to set pinfo_access.
* pinfo.cc (winpids::add): Try to open shared memory region with supplied
pinfo_access first, then default to readonly.
* fhandler_termios.cc (tty_min::kill_pgrp): When getting list of pids to work
with, suggest opening with PID_MAP_RW.
* signal.cc (kill_pgrp): Ditto.
* sigproc.cc (sig_send): Perform a write check on todo prior to attempting to
increment it.  Return EACCES if we can't write to it.

winsup/cygwin/sigproc.cc

@@ -725,6 +725,11 @@ sig_send (_pinfo *p, int sig, DWORD ebp, bool exception)
   else if ((thiscatch = getevent (p, "sigcatch")))
     {
       todo = p->getsigtodo (sig);
+      if (IsBadWritePtr (todo, sizeof (*todo)))
+	{
+	  set_errno (EACCES);
+	  goto out;
+	}
       issem = false;
     }
   else