black holes have a n infinite density as it's volume is zero so it is compressed to the very limit so it also has infinite gravity and so it sucks anything which is near it ! Not everything  there is!! Now above all when it sucks things it adds up to it's mass which remains finite and it always will as even if it did suck the whole universe!! It's all for the formula density in a black hole is mass divided by volume (0) so the density is infinite not the mass !!! So thus a black hole has mass which is finite and will always be finite.