Fix an off-by-one error checking the allocation of subject in task data.

Fixes #3 for 5.1.

src/tests/c01.vtc

@@ -143,3 +143,37 @@ client c1 {
 	expect resp.http.frap == "_barf_frap_"
 	expect resp.http.frapd == "_barf_frap_"
 } -run
+
+# Test copying the subject into private task-scoped data
+varnish v1 -vcl {
+	import re from "${vmod_topbuild}/src/.libs/libvmod_re.so";
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new bar = re.regex("bar");
+	}
+
+	sub vcl_recv {
+	    return(synth(200));
+	}
+
+	sub vcl_synth {
+	    if (bar.match("bar45678")) {
+	       set resp.http.bar8 = bar.backref(0);
+	    }
+	    if (bar.match("bar456789")) {
+	       set resp.http.bar9 = bar.backref(0);
+	    }
+	    if (bar.match("bar4567")) {
+	       set resp.http.bar7 = bar.backref(0);
+	    }
+	}
+}
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.http.bar7 == "bar"
+	expect resp.http.bar8 == "bar"
+	expect resp.http.bar9 == "bar"
+} -run

src/vmod_re.c

@@ -217,7 +217,7 @@ backref(VRT_CTX, VCL_INT refnum, VCL_STRING fallback, struct vmod_priv *task)
 
 	WS_Assert_Allocated(ctx->ws, task->priv, sizeof(*ov) - 1);
 	CAST_OBJ(ov, task->priv, OV_MAGIC);
-	WS_Assert_Allocated(ctx->ws, ov->subject, -1);
+	WS_Assert_Allocated(ctx->ws, ov->subject, strlen(ov->subject) - 1);
 
 	refnum <<= 1;
 	assert(refnum + 1 < MAX_OV_USED);