libceph: fix watch_item_t decoding to use ceph_decode_entity_addr

While we're in there, let's also fix up the decoder to do proper
bounds checking.
Signed-off-by: NJeff Layton <jlayton@kernel.org>
Reviewed-by: N"Yan, Zheng" <zyan@redhat.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

net/ceph/osd_client.c

@@ -4914,20 +4914,26 @@ static int decode_watcher(void **p, void *end, struct ceph_watch_item *item)
 	ret = ceph_start_decoding(p, end, 2, "watch_item_t",
 				  &struct_v, &struct_len);
 	if (ret)
-		return ret;
+		goto bad;
+
+	ret = -EINVAL;
+	ceph_decode_copy_safe(p, end, &item->name, sizeof(item->name), bad);
+	ceph_decode_64_safe(p, end, item->cookie, bad);
+	ceph_decode_skip_32(p, end, bad); /* skip timeout seconds */
 
-	ceph_decode_copy(p, &item->name, sizeof(item->name));
-	item->cookie = ceph_decode_64(p);
-	*p += 4; /* skip timeout_seconds */
 	if (struct_v >= 2) {
-		ceph_decode_copy(p, &item->addr, sizeof(item->addr));
-		ceph_decode_addr(&item->addr);
+		ret = ceph_decode_entity_addr(p, end, &item->addr);
+		if (ret)
+			goto bad;
+	} else {
+		ret = 0;
 	}
 
 	dout("%s %s%llu cookie %llu addr %s\n", __func__,
 	     ENTITY_NAME(item->name), item->cookie,
 	     ceph_pr_addr(&item->addr));
-	return 0;
+bad:
+	return ret;
 }
 
 static int decode_watchers(void **p, void *end,