user_signal-v3.patch

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index e7f7fe0..cf77586 100644
*** a/doc/src/sgml/func.sgml
--- b/doc/src/sgml/func.sgml
*************** SELECT set_config('log_statement_stats',
*** 14244,14251 ****
     <para>
      The functions shown in <xref
      linkend="functions-admin-signal-table"> send control signals to
!     other server processes.  Use of these functions is restricted
!     to superusers.
     </para>
  
     <table id="functions-admin-signal-table">
--- 14244,14251 ----
     <para>
      The functions shown in <xref
      linkend="functions-admin-signal-table"> send control signals to
!     other server processes.  Use of these functions is usually restricted
!     to superusers, with noted exceptions.
     </para>
  
     <table id="functions-admin-signal-table">
*************** SELECT set_config('log_statement_stats',
*** 14262,14268 ****
          <literal><function>pg_cancel_backend(<parameter>pid</parameter> <type>int</>)</function></literal>
          </entry>
         <entry><type>boolean</type></entry>
!        <entry>Cancel a backend's current query</entry>
        </row>
        <row>
         <entry>
--- 14262,14271 ----
          <literal><function>pg_cancel_backend(<parameter>pid</parameter> <type>int</>)</function></literal>
          </entry>
         <entry><type>boolean</type></entry>
!        <entry>Cancel a backend's current query.  You can execute this against
!         another backend that has exactly the same role as the user calling the
!         function.  In all other cases, you must be a superuser.
!         </entry>
        </row>
        <row>
         <entry>
*************** SELECT set_config('log_statement_stats',
*** 14304,14309 ****
--- 14307,14316 ----
      <command>postgres</command> processes on the server (using
      <application>ps</> on Unix or the <application>Task
      Manager</> on <productname>Windows</>).
+     For the less restrictive <function>pg_cancel_backend</>, the role of an
+     active backend can be found from
+     the <structfield>usename</structfield> column of the
+     <structname>pg_stat_activity</structname> view.
     </para>
  
     <para>
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index 7a2e0c8..1b7b75b 100644
*** a/src/backend/utils/adt/misc.c
--- b/src/backend/utils/adt/misc.c
***************
*** 30,35 ****
--- 30,36 ----
  #include "postmaster/syslogger.h"
  #include "storage/fd.h"
  #include "storage/pmsignal.h"
+ #include "storage/proc.h"
  #include "storage/procarray.h"
  #include "tcop/tcopprot.h"
  #include "utils/builtins.h"
*************** current_query(PG_FUNCTION_ARGS)
*** 70,84 ****
  }
  
  /*
!  * Functions to send signals to other backends.
   */
  static bool
! pg_signal_backend(int pid, int sig)
  {
! 	if (!superuser())
  		ereport(ERROR,
  				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
! 			(errmsg("must be superuser to signal other server processes"))));
  
  	if (!IsBackendPid(pid))
  	{
--- 71,113 ----
  }
  
  /*
!  * Send a signal to another backend
   */
  static bool
! pg_signal_backend(int pid, int sig, bool allow_same_role)
  {
! 	PGPROC	*proc;
! 	bool	allowed = superuser();
! 
! 	if (!allowed && allow_same_role)
! 	{
! 		/*
! 		 * When same role permission is allowed, check for matching roles.  Trust
! 		 * that BackendPidGetProc will return NULL if the pid isn't valid, even
! 		 * though the check for whether it's a backend process is below.  The
! 		 * IsBackendPid check can't be relied on as definitive even if it was
! 		 * first.  The process might end between successive checks regardless of
! 		 * their order.  There's no way to acquire a lock on an arbitrary
! 		 * process to prevent that.  But since so far all the callers of this
! 		 * mechanism involve some request for ending the process anyway, that
! 		 * it might end on its own first is not a problem.
! 		 */
! 		proc = BackendPidGetProc(pid);
! 
! 		if ((proc != NULL) && (proc->roleId == GetUserId()))
! 			allowed = true;
! 		else
! 			ereport(ERROR,
! 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
! 					(errmsg("must be superuser or have the same role to signal other server processes"))));
! 	}
! 
! 	/* Rejected the same role case above, must be superuser only by here */
! 	if (!allowed)
  		ereport(ERROR,
  				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
! 				errmsg("must be superuser to terminate other server processes"),
! 				errhint("You can cancel your own processes with pg_cancel_backend().")));
  
  	if (!IsBackendPid(pid))
  	{
*************** pg_signal_backend(int pid, int sig)
*** 91,96 ****
--- 120,134 ----
  		return false;
  	}
  
+ 	/*
+ 	 * Can the process we just validated above end, followed by the pid being
+ 	 * recycled for a new process, before reaching here?  Then we'd be trying to
+ 	 * kill the wrong thing.  Seems near impossible when sequential pid
+ 	 * assignment and wraparound is used.  Perhaps it could happen on a system
+ 	 * where pid re-use is randomized.  That race condition possibility seems
+ 	 * too unlikely to worry about.
+ 	 */
+ 
  	/* If we have setsid(), signal the backend's whole process group */
  #ifdef HAVE_SETSID
  	if (kill(-pid, sig))
*************** pg_signal_backend(int pid, int sig)
*** 106,123 ****
  	return true;
  }
  
  Datum
  pg_cancel_backend(PG_FUNCTION_ARGS)
  {
! 	PG_RETURN_BOOL(pg_signal_backend(PG_GETARG_INT32(0), SIGINT));
  }
  
  Datum
  pg_terminate_backend(PG_FUNCTION_ARGS)
  {
! 	PG_RETURN_BOOL(pg_signal_backend(PG_GETARG_INT32(0), SIGTERM));
  }
  
  Datum
  pg_reload_conf(PG_FUNCTION_ARGS)
  {
--- 144,171 ----
  	return true;
  }
  
+ /*
+  * Signal to cancel a backend process.  This is allowed if you are superuser or
+  * have the same role as the process being canceled.
+  */
  Datum
  pg_cancel_backend(PG_FUNCTION_ARGS)
  {
! 	PG_RETURN_BOOL(pg_signal_backend(PG_GETARG_INT32(0), SIGINT, true));
  }
  
+ /*
+  * Signal to terminate a backend process.  Only allowed by superuser.
+  */
  Datum
  pg_terminate_backend(PG_FUNCTION_ARGS)
  {
! 	PG_RETURN_BOOL(pg_signal_backend(PG_GETARG_INT32(0), SIGTERM, false));
  }
  
+ /*
+  * Signal to reload the database configuration
+  */
  Datum
  pg_reload_conf(PG_FUNCTION_ARGS)
  {