[PATCH nf] netfilter: nft_compat: tighten the nft_compat interface

[Florian Westphal <fw@strlen.de>]

nft_compat is used by xtables-over-nftables:
 - arptables-nft
 - ebtables-nft
 - iptables-nft
 - ip6tables-nft

x_tables doesn't support NFPROTO_NETDEV and NFPROTO_INET.
Reject unsupported families. As-is, this allows use of xtables
NFPROTO_UNSPEC extensions that are crashing the kernel when used
with e.g. NFPROTO_NETDEV.

NFPROTO_INET *might* be safe (since its a superset of
NFPROTO_IPV4/IPV6), but it is not used by the existing compat
layer.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 This is in addition to
 "netfilter: x_tables: reject unsupported families in xt_check_match/xt_check_target".

 net/netfilter/nft_compat.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index 27cc983a7cdf..bafc0bf450e6 100644
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -786,6 +786,20 @@ static bool nft_match_reduce(struct nft_regs_track *track,
 	return strcmp(match->name, "comment") == 0;
 }
 
+static bool is_valid_compat_family(u32 family)
+{
+	switch (family) {
+	case NFPROTO_IPV4:
+	case NFPROTO_ARP:
+	case NFPROTO_BRIDGE:
+	case NFPROTO_IPV6:
+		return true;
+	}
+
+	/* others are nftables only */
+	return false;
+}
+
 static const struct nft_expr_ops *
 nft_match_select_ops(const struct nft_ctx *ctx,
 		     const struct nlattr * const tb[])
@@ -806,6 +820,9 @@ nft_match_select_ops(const struct nft_ctx *ctx,
 	rev = ntohl(nla_get_be32(tb[NFTA_MATCH_REV]));
 	family = ctx->family;
 
+	if (!is_valid_compat_family(family))
+		return ERR_PTR(-EAFNOSUPPORT);
+
 	match = xt_request_find_match(family, mt_name, rev);
 	if (IS_ERR(match))
 		return ERR_PTR(-ENOENT);
@@ -886,6 +903,9 @@ nft_target_select_ops(const struct nft_ctx *ctx,
 	rev = ntohl(nla_get_be32(tb[NFTA_TARGET_REV]));
 	family = ctx->family;
 
+	if (!is_valid_compat_family(family))
+		return ERR_PTR(-EAFNOSUPPORT);
+
 	if (strcmp(tg_name, XT_ERROR_TARGET) == 0 ||
 	    strcmp(tg_name, XT_STANDARD_TARGET) == 0 ||
 	    strcmp(tg_name, "standard") == 0)
-- 
2.53.0