Use req->ws in the ctx when piping

Previously bo->ws was used which led to workspace mixing. req->ws safely
outlives both the bo and req object when piping.

bin/varnishd/cache/cache_vrt_vcl.c

@@ -459,11 +459,13 @@ vcl_call_method(struct worker *wrk, struct req *req, struct busyobj *bo,
 		VCL_Req2Ctx(&ctx, req);
 	}
 	if (bo != NULL) {
-		if (req)
-			assert(method == VCL_MET_PIPE);
 		CHECK_OBJ_NOTNULL(bo, BUSYOBJ_MAGIC);
 		CHECK_OBJ_NOTNULL(bo->vcl, VCL_MAGIC);
 		VCL_Bo2Ctx(&ctx, bo);
+		if (req) {
+			assert(method == VCL_MET_PIPE);
+			ctx.ws = req->ws;
+		}
 	}
 	assert(ctx.now != 0);
 	ctx.specific = specific;

bin/varnishtest/tests/r03329.vtc

+varnishtest "Lost reason from pipe to synth"
+
+server s1 {} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_recv {
+		return (pipe);
+	}
+	sub vcl_pipe {
+		return (synth(505, req.http.foo + "/bar"));
+	}
+} -start
+
+client c1 {
+	txreq -hdr "foo: foo"
+	rxresp
+	expect resp.reason == "foo/bar"
+} -run

bin/varnishtest/tests/r03385.vtc

+varnishtest "Use a priv in vcl_pipe"
+
+server s1 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+	import debug;
+
+	sub vcl_recv {
+		return (pipe);
+	}
+
+	sub vcl_pipe {
+		debug.test_priv_task();
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+} -run