From bcde9a5b4964aba50f65253e0f1aaa967a6f9e34 Mon Sep 17 00:00:00 2001
From: Andy Green <andy@warmcat.com>
Date: Sun, 12 May 2024 05:27:43 +0100
Subject: [PATCH] lhp: assert if NULL css stack coming to lws_csp_px

iwashiira on github https://github.com/warmcat/libwebsockets/issues/3140
found the html / css calculation could end up with NULL margin sizes.

This causes an assert if we get this unacceptable situation as far as
lws_csp_px()
---
 lib/misc/lhp.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/misc/lhp.c b/lib/misc/lhp.c
index 59a227d84..73fd663f6 100644
--- a/lib/misc/lhp.c
+++ b/lib/misc/lhp.c
@@ -312,14 +312,19 @@ lws_css_compute_cascaded_length(lhp_ctx_t *ctx, int ref, lhp_pstack_t *ps,
 const lws_fx_t *
 lws_csp_px(const lcsp_atr_t *a, lhp_pstack_t *ps)
 {
-	lhp_ctx_t *ctx = lws_container_of(ps->list.owner, lhp_ctx_t, stack);
-	const lws_display_font_t *f = ps->font;
+	lhp_ctx_t *ctx;
+	const lws_display_font_t *f;
 	lws_fx_t t1, t2, t3;
 	int ref;
 
+	assert(ps);
+
 	if (!a)
 		return NULL;
 
+	ctx = lws_container_of(ps->list.owner, lhp_ctx_t, stack);
+	f = ps->font;
+
 	ref = lhp_prop_axis(a);
 
 	switch (a->unit) {