commit f09418bbb6651ab4c299cfefbe1d18de401f630e
from: bakkeby <bakkeby@gmail.com>
via: Hiltjo Posthuma <hiltjo@codemadness.org>
date: Sat Apr 25 11:31:02 2020 UTC

dwm crashes when opening 50+ clients (tile layout)

Many users new to dwm find themselves caught out by being kicked out to the login manager (dwm crashing) when they open 50+ clients for demonstration purposes. The number of clients reported varies depending on the resolution of the monitor.

The cause of this is due to how the default tile layout calculates the height of the next client based on the position of the previous client. Because clients have a minimum size the (ty) position can exceed that of the window height, resulting in (m->wh - ty) becoming negative. The negative height stored as an unsigned int results in a very large height ultimately resulting in dwm crashing.

This patch adds safeguards to prevent the ty and my positions from exceeding that of the window height.

commit - ed3ab6b4fceded0e9f2d22372df49a2bbd58de66
commit + f09418bbb6651ab4c299cfefbe1d18de401f630e
blob - fb1e32634abb830aeff0f9b51e92742130cf8e44
blob + 9fd02862ca58529cf4f07cc4d3469e2b43a532b8
--- dwm.c
+++ dwm.c
@@ -1689,11 +1689,13 @@ tile(Monitor *m)
 		if (i < m->nmaster) {
 			h = (m->wh - my) / (MIN(n, m->nmaster) - i);
 			resize(c, m->wx, m->wy + my, mw - (2*c->bw), h - (2*c->bw), 0);
-			my += HEIGHT(c);
+			if (my + HEIGHT(c) < m->wh)
+				my += HEIGHT(c);
 		} else {
 			h = (m->wh - ty) / (n - i);
 			resize(c, m->wx + mw, m->wy + ty, m->ww - mw - (2*c->bw), h - (2*c->bw), 0);
-			ty += HEIGHT(c);
+			if (ty + HEIGHT(c) < m->wh)
+				ty += HEIGHT(c);
 		}
 }