Check VRT_StrandsWS() return value

Fixes: VSV00006

src/Makefile.am

@@ -96,6 +96,8 @@ VMOD_TESTS = \
 	tests/bodyaccess/test04.vtc \
 	tests/bodyaccess/test05.vtc \
 	tests/header/append.vtc \
+	tests/header/append_maxhdr_overflow.vtc \
+	tests/header/append_overflow.vtc \
 	tests/header/copy.vtc \
 	tests/header/get.vtc \
 	tests/header/import.vtc \

src/tests/header/append_maxhdr_overflow.vtc

@@ -0,0 +1,45 @@
+varnishtest "header.append with http_max_hdr and overflow"
+
+varnish v1 -arg "-p http_max_hdr=32" -vcl {
+	backend proforma None;
+
+	import vtc;
+	import std;
+	import header from "${vmod_builddir}/.libs/libvmod_header.so";
+
+	sub vcl_recv {
+		std.log(vtc.workspace_free(client));
+		header.append(req.http.foo, "bar");
+	}
+} -start
+
+client c1 {
+	txreq \
+		-hdr "0: 1" \
+		-hdr "1: 1" \
+		-hdr "2: 1" \
+		-hdr "3: 1" \
+		-hdr "4: 1" \
+		-hdr "5: 1" \
+		-hdr "6: 1" \
+		-hdr "7: 1" \
+		-hdr "8: 1" \
+		-hdr "9: 1" \
+		-hdr "a: 1" \
+		-hdr "b: 1" \
+		-hdr "c: 1" \
+		-hdr "d: 1" \
+		-hdr "e: 1" \
+		-hdr "f: 1" \
+		-hdr "10: 1" \
+		-hdr "11: 1" \
+		-hdr "12: 1" \
+		-hdr "13: 1" \
+		-hdr "14: 1" \
+		-hdr "15: 1" \
+		-hdr "16: 1" \
+		-hdr "17: 1" \
+		-hdr "18: 1" \
+		-hdr "19: 1"
+	rxresp
+} -run

src/tests/header/append_overflow.vtc

@@ -0,0 +1,18 @@
+varnishtest "header.append overflow"
+
+varnish v1 -vcl {
+	backend proforma None;
+
+	import vtc;
+	import header from "${vmod_builddir}/.libs/libvmod_header.so";
+
+	sub vcl_recv {
+		vtc.workspace_alloc(client, -2);
+		header.append(req.http.foo, "bar");
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+} -run

src/vmod_header.c

@@ -226,6 +226,10 @@ vmod_append(VRT_CTX, VCL_HEADER hdr, VCL_STRANDS s)
 	st->p = p;
 
 	b = VRT_StrandsWS(ctx->ws, NULL, st);
+	if (b == NULL) {
+		VRT_fail(ctx, "vmod_header: workspace allocation failure");
+		return;
+	}
 
 	hp = VRT_selecthttp(ctx, hdr->where);
 	http_SetHeader(hp, b);