[nf-next PATCH v3] netfilter: nf_tables: Reject tables of unsupported family

[nf-next PATCH v3] netfilter: nf_tables: Reject tables of unsupported family

[Phil Sutter]

An nftables family is merely a hollow container, its family just a
number and such not reliant on compile-time options other than nftables
support itself. Add an artificial check so attempts at using a family
the kernel can't support fail as early as possible. This helps user
space detect kernels which lack e.g. NFPROTO_INET.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
Changes since v2:
- Casting family from u8 to int via parameter resulted in an always
  negative result. Pass it as u8 to nft_supported_family().
- Fix typo: CONIFG_NF_TABLES_BRIDGE -> CONFIG_NF_TABLES_BRIDGE
- Reduce the function to a single statement instead of if/else
  conditional.
- Use 'false' instead of '0' for the standard term.

Changes since v1:
- Avoid a compiler warning if none of the tested symbols are enabled.
---
 net/netfilter/nf_tables_api.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 5fa16990da951..ac33ca9f8d88b 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1072,6 +1072,30 @@ static int nft_objname_hash_cmp(struct rhashtable_compare_arg *arg,
 	return strcmp(obj->key.name, k->name);
 }
 
+static bool nft_supported_family(u8 family)
+{
+	return false
+#ifdef CONFIG_NF_TABLES_INET
+		|| family == NFPROTO_INET
+#endif
+#ifdef CONFIG_NF_TABLES_IPV4
+		|| family == NFPROTO_IPV4
+#endif
+#ifdef CONFIG_NF_TABLES_ARP
+		|| family == NFPROTO_ARP
+#endif
+#ifdef CONFIG_NF_TABLES_NETDEV
+		|| family == NFPROTO_NETDEV
+#endif
+#if IS_ENABLED(CONFIG_NF_TABLES_BRIDGE)
+		|| family == NFPROTO_BRIDGE
+#endif
+#ifdef CONFIG_NF_TABLES_IPV6
+		|| family == NFPROTO_IPV6
+#endif
+		;
+}
+
 static int nf_tables_newtable(struct sk_buff *skb, const struct nfnl_info *info,
 			      const struct nlattr * const nla[])
 {
@@ -1086,6 +1110,9 @@ static int nf_tables_newtable(struct sk_buff *skb, const struct nfnl_info *info,
 	u32 flags = 0;
 	int err;
 
+	if (!nft_supported_family(family))
+		return -EOPNOTSUPP;
+
 	lockdep_assert_held(&nft_net->commit_mutex);
 	attr = nla[NFTA_TABLE_NAME];
 	table = nft_table_lookup(net, attr, family, genmask,
-- 
2.34.1

Re: [nf-next PATCH v3] netfilter: nf_tables: Reject tables of unsupported family

[Pablo Neira Ayuso]

On Wed, Feb 16, 2022 at 03:55:38PM +0100, Phil Sutter wrote:
> An nftables family is merely a hollow container, its family just a
> number and such not reliant on compile-time options other than nftables
> support itself. Add an artificial check so attempts at using a family
> the kernel can't support fail as early as possible. This helps user
> space detect kernels which lack e.g. NFPROTO_INET.

Applied, thanks