[PATCH nf] netfilter: nf_tables: don't fail when updating base chain policy

[Florian Westphal <fw@strlen.de>]

The following nftables test case fails on nf-next:

tests/shell/run-tests.sh tests/shell/testcases/transactions/0011chain_0

The test case contains:
add chain x y { type filter hook input priority 0; }
add chain x y { policy drop; }"

The new test
if (chain->flags ^ flags)
	return -EOPNOTSUPP;

triggers here, because chain->flags has NFT_BASE_CHAIN set, but flags
is 0 because no flag attribute was present in the policy update.

Just fetch the current flag settings of a pre-existing chain in case
userspace did not provide any.

Fixes: c9626a2cbdb20 ("netfilter: nf_tables: add hardware offload support")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nf_tables_api.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index add64bd227a8..5746a7c948fe 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1914,6 +1914,8 @@ static int nf_tables_newchain(struct net *net, struct sock *nlsk,
 
 	if (nla[NFTA_CHAIN_FLAGS])
 		flags = ntohl(nla_get_be32(nla[NFTA_CHAIN_FLAGS]));
+	else if (chain)
+		flags = chain->flags;
 
 	nft_ctx_init(&ctx, net, skb, nlh, family, table, chain, nla);
 
-- 
2.21.0