Bug: leave_prog can crash the game by closing an exit
Danger: High - Groups travelling through a room with a leave_prog that closes an exit stand a good chance of causing a crash.
Discovered in: AFKMud 1.77
Found by: Valcados
Fixed by: Samson/Remcon

---

act_move.c, move_char

Locate:

               if( !IS_NPC( fch ) )
               {
                  /*
                   * Added checks so morts don't blindly follow the leader into DT's. 
                   * -- Tarl 16 July 2002 
                   */
                  if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
                     send_to_char( "You stand your ground.", fch );
                  else
                  {
                     act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                     move_char( fch, pexit, 0, direction, running );
                  }
               }

Change to:

               if( !IS_NPC( fch ) )
               {
                  /*
                   * Added checks so morts don't blindly follow the leader into DT's. 
                   * -- Tarl 16 July 2002 
                   */
                  if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
                     send_to_char( "You stand your ground.", fch );
                  else
                  {
                     if( !get_exit( from_room, direction ) )
                     {
                        act( AT_ACTION, "The entrance closes behind $N, preventing you from following!", fch, NULL, ch, TO_CHAR );
                        continue;
                     }
                     act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                     move_char( fch, pexit, 0, direction, running );
                  }
               }

Locate:

               if( fch != ch  /* loop room bug fix here by Thoric */
                   && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
               {
                  if( !IS_NPC( fch ) )
                  {
                     /*
                      * Added checks so morts don't blindly follow the leader into DT's. 
                      * -- Tarl 16 July 2002 
                      */
                     if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
                        send_to_char( "You stand your ground.", fch );
                     else
                     {
                        act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                        move_char( fch, pexit, 0, direction, running );
                     }
                  }
                  else
                     enter_map( fch, pexit, pexit->x, pexit->y, -1 );
               }

Change to:

               if( fch != ch  /* loop room bug fix here by Thoric */
                   && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
               {
                  if( !IS_NPC( fch ) )
                  {
                     /*
                      * Added checks so morts don't blindly follow the leader into DT's. 
                      * -- Tarl 16 July 2002 
                      */
                     if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
                        send_to_char( "You stand your ground.", fch );
                     else
                     {
                        if( !get_exit( from_room, direction ) )
                        {
                           act( AT_ACTION, "The entrance closes behind $N, preventing you from following!", fch, NULL, ch, TO_CHAR );
                           continue;
                        }
                        act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                        move_char( fch, pexit, 0, direction, running );
                     }
                  }
                  else
                     enter_map( fch, pexit, pexit->x, pexit->y, -1 );
               }

Locate:

         if( fch != ch  /* loop room bug fix here by Thoric */
             && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
         {
            if( !running )
            {
               /*
                * Added checks so morts don't blindly follow the leader into DT's.
                * -- Tarl 16 July 2002 
                */
               if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
                  send_to_char( "You stand your ground.", fch );
               else
                  act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
            }
            if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
               send_to_char( "You decide to wait here.", fch );
            else
               move_char( fch, pexit, 0, direction, running );
         }

Change to:

         if( fch != ch  /* loop room bug fix here by Thoric */
             && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
         {
            if( !running )
            {
               /*
                * Added checks so morts don't blindly follow the leader into DT's.
                * -- Tarl 16 July 2002 
                */
               if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
                  send_to_char( "You stand your ground.", fch );
               else
               {
                  if( !get_exit( from_room, direction ) )
                  {
                     act( AT_ACTION, "The entrance closes behind $N, preventing you from following!", fch, NULL, ch, TO_CHAR );
                     continue;
                  }
                  act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
               }
            }
            if( IS_ROOM_FLAG( pexit->to_room, ROOM_DEATH ) )
               send_to_char( "You decide to wait here.", fch );
            else
               move_char( fch, pexit, 0, direction, running );
         }

ships.c, move_ship

Locate:

         for( fch = from_room->first_person; fch && ( count < chars ); fch = nextinroom )
         {
            nextinroom = fch->next_in_room;
            count++;
            if( fch != ch  /* loop room bug fix here by Thoric */
                && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
            {
               if( !IS_NPC( fch ) )
               {
                  act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                  move_char( fch, pexit, 0, direction, FALSE );
               }
               else
                  enter_map( fch, pexit, pexit->x, pexit->y, -1 );
            }
         }

Change to:

         for( fch = from_room->first_person; fch && ( count < chars ); fch = nextinroom )
         {
            nextinroom = fch->next_in_room;
            count++;
            if( fch != ch  /* loop room bug fix here by Thoric */
                && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
            {
               if( !IS_NPC( fch ) )
               {
                  if( !get_exit( from_room, direction ) )
                  {
                     act( AT_ACTION, "The entrance closes behind $N, preventing you from following!", fch, NULL, ch, TO_CHAR );
                     continue;
                  }
                  act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                  move_char( fch, pexit, 0, direction, FALSE );
               }
               else
                  enter_map( fch, pexit, pexit->x, pexit->y, -1 );
            }
         }

Locate:

            for( fch = from_room->first_person; fch && ( count < chars ); fch = nextinroom )
            {
               nextinroom = fch->next_in_room;
               count++;
               if( fch != ch  /* loop room bug fix here by Thoric */
                   && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
               {
                  if( !IS_NPC( fch ) )
                  {
                     act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                     move_char( fch, pexit, 0, direction, FALSE );
                  }
                  else
                     enter_map( fch, pexit, pexit->x, pexit->y, -1 );
               }
            }

Change to:

            for( fch = from_room->first_person; fch && ( count < chars ); fch = nextinroom )
            {
               nextinroom = fch->next_in_room;
               count++;
               if( fch != ch  /* loop room bug fix here by Thoric */
                   && fch->master == ch && ( fch->position == POS_STANDING || fch->position == POS_MOUNTED ) )
               {
                  if( !IS_NPC( fch ) )
                  {
                     if( !get_exit( from_room, direction ) )
                     {
                        act( AT_ACTION, "The entrance closes behind $N, preventing you from following!", fch, NULL, ch, TO_CHAR );
                        continue;
                     }
                     act( AT_ACTION, "You follow $N.", fch, NULL, ch, TO_CHAR );
                     move_char( fch, pexit, 0, direction, FALSE );
                  }
                  else
                     enter_map( fch, pexit, pexit->x, pexit->y, -1 );
               }
            }

Ordinarily not much of a problem. But if a room has a leave_prog which closes an exit that the group is trying to follow the leader through, the game will probably crash. The reason being is that the exit pointer that move_char has gets removed when the exit is extracted. So the following loop is trying to use an invalid pointer. So to prevent this and other methods of exit removal from causing a crash, the exit pointer needs to be validated for every follower in the group.

A much more involved alternative fix is also available here: http://smaugmuds.afkmods.com/index.php?a=topic&t=2212