[master] 4537efefd ws: Put canaries all the way to the end of the workspace

[Dridi Boukelmoune]

commit 4537efefd3eee3778a367503d8da8c674102578b
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Thu May 7 18:55:40 2020 +0200

    ws: Put canaries all the way to the end of the workspace
    
    It might help catch more buffer overflows, although we still only check
    the first byte.

diff --git a/bin/varnishd/cache/cache_ws.c b/bin/varnishd/cache/cache_ws.c
index c8fb32210..4e09b59ae 100644
--- a/bin/varnishd/cache/cache_ws.c
+++ b/bin/varnishd/cache/cache_ws.c
@@ -98,6 +98,7 @@ WS_Assert_Allocated(const struct ws *ws, const void *ptr, ssize_t len)
 void
 WS_Init(struct ws *ws, const char *id, void *space, unsigned len)
 {
+	unsigned l;
 
 	DSL(DBG_WORKSPACE, 0,
 	    "WS_Init(%p, \"%s\", %p, %u)", ws, id, space, len);
@@ -105,9 +106,9 @@ WS_Init(struct ws *ws, const char *id, void *space, unsigned len)
 	INIT_OBJ(ws, WS_MAGIC);
 	ws->s = space;
 	assert(PAOK(space));
-	len = PRNDDN(len - 1);
-	ws->e = ws->s + len;
-	*ws->e = WS_REDZONE_END;
+	l = PRNDDN(len - 1);
+	ws->e = ws->s + l;
+	memset(ws->e, WS_REDZONE_END, len - l);
 	ws->f = ws->s;
 	assert(id[0] & 0x20);		// cheesy islower()
 	bstrcpy(ws->id, id);