netfilter: nft_socket: add support for cgroupsv2

Allow to match on the cgroupsv2 id from ancestor level.

Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/uapi/linux/netfilter/nf_tables.h

···
  *
  * @NFTA_SOCKET_KEY: socket key to match
  * @NFTA_SOCKET_DREG: destination register
+ * @NFTA_SOCKET_LEVEL: cgroups2 ancestor level (only for cgroupsv2)
  */
 enum nft_socket_attributes {
 	NFTA_SOCKET_UNSPEC,
 	NFTA_SOCKET_KEY,
 	NFTA_SOCKET_DREG,
+	NFTA_SOCKET_LEVEL,
 	__NFTA_SOCKET_MAX
 };
 #define NFTA_SOCKET_MAX		(__NFTA_SOCKET_MAX - 1)
···
  * @NFT_SOCKET_TRANSPARENT: Value of the IP(V6)_TRANSPARENT socket option
  * @NFT_SOCKET_MARK: Value of the socket mark
  * @NFT_SOCKET_WILDCARD: Whether the socket is zero-bound (e.g. 0.0.0.0 or ::0)
+ * @NFT_SOCKET_CGROUPV2: Match on cgroups version 2
  */
 enum nft_socket_keys {
 	NFT_SOCKET_TRANSPARENT,
 	NFT_SOCKET_MARK,
 	NFT_SOCKET_WILDCARD,
+	NFT_SOCKET_CGROUPV2,
 	__NFT_SOCKET_MAX
 };
 #define NFT_SOCKET_MAX	(__NFT_SOCKET_MAX - 1)

net/netfilter/nft_socket.c

···
 
 struct nft_socket {
 	enum nft_socket_keys		key:8;
+	u8				level;
 	union {
 		u8			dreg;
 	};
···
 		return;
 	}
 }
+
+#ifdef CONFIG_CGROUPS
+static noinline bool
+nft_sock_get_eval_cgroupv2(u32 *dest, const struct nft_pktinfo *pkt, u32 level)
+{
+	struct sock *sk = skb_to_full_sk(pkt->skb);
+	struct cgroup *cgrp;
+
+	if (!sk || !sk_fullsock(sk) || !net_eq(nft_net(pkt), sock_net(sk)))
+		return false;
+
+	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
+	if (level > cgrp->level)
+		return false;
+
+	memcpy(dest, &cgrp->ancestor_ids[level], sizeof(u64));
+
+	return true;
+}
+#endif
 
 static void nft_socket_eval(const struct nft_expr *expr,
 			    struct nft_regs *regs,
···
 		}
 		nft_socket_wildcard(pkt, regs, sk, dest);
 		break;
+#ifdef CONFIG_CGROUPS
+	case NFT_SOCKET_CGROUPV2:
+		if (!nft_sock_get_eval_cgroupv2(dest, pkt, priv->level)) {
+			regs->verdict.code = NFT_BREAK;
+			return;
+		}
+		break;
+#endif
 	default:
 		WARN_ON(1);
 		regs->verdict.code = NFT_BREAK;
···
 static const struct nla_policy nft_socket_policy[NFTA_SOCKET_MAX + 1] = {
 	[NFTA_SOCKET_KEY]		= { .type = NLA_U32 },
 	[NFTA_SOCKET_DREG]		= { .type = NLA_U32 },
+	[NFTA_SOCKET_LEVEL]		= { .type = NLA_U32 },
 };
 
 static int nft_socket_init(const struct nft_ctx *ctx,
···
 			   const struct nlattr * const tb[])
 {
 	struct nft_socket *priv = nft_expr_priv(expr);
-	unsigned int len;
+	unsigned int len, level;
 
 	if (!tb[NFTA_SOCKET_DREG] || !tb[NFTA_SOCKET_KEY])
 		return -EINVAL;
···
 	case NFT_SOCKET_MARK:
 		len = sizeof(u32);
 		break;
+#ifdef CONFIG_CGROUPS
+	case NFT_SOCKET_CGROUPV2:
+		if (!tb[NFTA_SOCKET_LEVEL])
+			return -EINVAL;
+
+		level = ntohl(nla_get_u32(tb[NFTA_SOCKET_LEVEL]));
+		if (level > 255)
+			return -EOPNOTSUPP;
+
+		priv->level = level;
+		len = sizeof(u64);
+		break;
+#endif
 	default:
 		return -EOPNOTSUPP;
 	}
···
 	if (nla_put_u32(skb, NFTA_SOCKET_KEY, htonl(priv->key)))
 		return -1;
 	if (nft_dump_register(skb, NFTA_SOCKET_DREG, priv->dreg))
+		return -1;
+	if (priv->key == NFT_SOCKET_CGROUPV2 &&
+	    nla_put_u32(skb, NFTA_SOCKET_LEVEL, htonl(priv->level)))
 		return -1;
 	return 0;
 }