Fix missed adjustments to vsl buffer space checks

Refs 8df30240

Fixes #3856

bin/varnishd/cache/cache_shmlog.c

@@ -382,18 +382,18 @@ VSLbs(struct vsl_log *vsl, enum VSL_tag_e tag, const struct strands *s)
 	/* including NUL */
 	l = vmin_t(unsigned, strands_len(s) + 1, mlen);
 
-	assert(vsl->wlp < vsl->wle);
+	assert(vsl->wlp <= vsl->wle);
 
 	/* Flush if necessary */
-	if (VSL_END(vsl->wlp, l) >= vsl->wle)
+	if (VSL_END(vsl->wlp, l) > vsl->wle)
 		VSL_Flush(vsl, 1);
-	assert(VSL_END(vsl->wlp, l) < vsl->wle);
+	assert(VSL_END(vsl->wlp, l) <= vsl->wle);
 
 	mlen = strands_cat(VSL_DATA(vsl->wlp), l, s);
 	assert(l == mlen);
 
 	vsl->wlp = vsl_hdr(tag, vsl->wlp, l, vsl->wid);
-	assert(vsl->wlp < vsl->wle);
+	assert(vsl->wlp <= vsl->wle);
 	vsl->wlr++;
 
 	if (DO_DEBUG(DBG_SYNCVSL))

bin/varnishtest/tests/r03856.vtc

+varnishtest "Regression test off-by-one in VSLbs"
+
+# vsl_buffer=257 bytes - 2 bytes header -> 255 bytes
+
+varnish v1 -arg "-p vsl_buffer=267" -vcl {
+	import debug;
+	backend b None;
+	sub vcl_recv {
+
+		# Assert error in VSLbs(), cache/cache_shmlog.c line 385:
+		#   Condition(vsl->wlp < vsl->wle) not true.
+
+		debug.vsl_flush();
+		set req.http.a =
+			# 255 = "a: " + 8 * 32 - 4
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789ab";
+		debug.return_strands("xyz");
+
+		# Assert error in VSLbs(), cache/cache_shmlog.c line 390:
+		#   Condition(VSL_END(vsl->wlp, l) < vsl->wle) not true.
+		debug.vsl_flush();
+		debug.return_strands(
+			# 255 = 8 * 32 - 1
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcdef" +
+			"0123456789abcdef0123456789abcde");
+		return (synth(200));
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+} -run