netfilter: nft_log: fix snaplen does not truncate packets

There's a similar problem in xt_NFLOG, and was fixed by commit 7643507fe8b5
("netfilter: xt_NFLOG: nflog-range does not truncate packets"). Only set
copy_len here does not work, so we should enable NF_LOG_F_COPY_LEN also.

Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_log.c

@@ -92,6 +92,7 @@ static int nft_log_init(const struct nft_ctx *ctx,
 	case NF_LOG_TYPE_ULOG:
 		li->u.ulog.group = ntohs(nla_get_be16(tb[NFTA_LOG_GROUP]));
 		if (tb[NFTA_LOG_SNAPLEN] != NULL) {
+			li->u.ulog.flags |= NF_LOG_F_COPY_LEN;
 			li->u.ulog.copy_len =
 				ntohl(nla_get_be32(tb[NFTA_LOG_SNAPLEN]));
 		}
@@ -149,7 +150,7 @@ static int nft_log_dump(struct sk_buff *skb, const struct nft_expr *expr)
 		if (nla_put_be16(skb, NFTA_LOG_GROUP, htons(li->u.ulog.group)))
 			goto nla_put_failure;
 
-		if (li->u.ulog.copy_len) {
+		if (li->u.ulog.flags & NF_LOG_F_COPY_LEN) {
 			if (nla_put_be32(skb, NFTA_LOG_SNAPLEN,
 					 htonl(li->u.ulog.copy_len)))
 				goto nla_put_failure;