netfilter: nft_log: check the validity of log level

User can specify the log level larger than 7(debug level) via
nfnetlink, this is invalid. So in this case, we should report
EINVAL to the userspace.
Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_log.c

@@ -79,6 +79,11 @@ static int nft_log_init(const struct nft_ctx *ctx,
 		} else {
 			li->u.log.level = LOGLEVEL_WARNING;
 		}
+		if (li->u.log.level > LOGLEVEL_DEBUG) {
+			err = -EINVAL;
+			goto err1;
+		}
+
 		if (tb[NFTA_LOG_FLAGS] != NULL) {
 			li->u.log.logflags =
 				ntohl(nla_get_be32(tb[NFTA_LOG_FLAGS]));