flow_dissector: implements flow dissector BPF hook

Adds a hook for programs of type BPF_PROG_TYPE_FLOW_DISSECTOR and
attach type BPF_FLOW_DISSECTOR that is executed in the flow dissector
path. The BPF program is per-network namespace.
Signed-off-by: Petar Penkov <ppenkov@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -212,6 +212,7 @@ enum bpf_reg_type {
 	PTR_TO_PACKET_META,	 /* skb->data - meta_len */
 	PTR_TO_PACKET,		 /* reg points to skb->data */
 	PTR_TO_PACKET_END,	 /* skb->data + headlen */
+	PTR_TO_FLOW_KEYS,	 /* reg points to bpf_flow_keys */
 };
 
 /* The information passed from prog-specific *_is_valid_access

include/linux/bpf_types.h

@@ -32,6 +32,7 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_LIRC_MODE2, lirc_mode2)
 #ifdef CONFIG_INET
 BPF_PROG_TYPE(BPF_PROG_TYPE_SK_REUSEPORT, sk_reuseport)
 #endif
+BPF_PROG_TYPE(BPF_PROG_TYPE_FLOW_DISSECTOR, flow_dissector)
 
 BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)

include/linux/skbuff.h

@@ -243,6 +243,8 @@ struct scatterlist;
 struct pipe_inode_info;
 struct iov_iter;
 struct napi_struct;
+struct bpf_prog;
+union bpf_attr;
 
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
 struct nf_conntrack {
@@ -1192,6 +1194,11 @@ void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
 			     const struct flow_dissector_key *key,
 			     unsigned int key_count);
 
+int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
+				       struct bpf_prog *prog);
+
+int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr);
+
 bool __skb_flow_dissect(const struct sk_buff *skb,
 			struct flow_dissector *flow_dissector,
 			void *target_container,

include/net/net_namespace.h

@@ -43,6 +43,7 @@ struct ctl_table_header;
 struct net_generic;
 struct uevent_sock;
 struct netns_ipvs;
+struct bpf_prog;
 
 
 #define NETDEV_HASHBITS    8
@@ -145,6 +146,8 @@ struct net {
 #endif
 	struct net_generic __rcu	*gen;
 
+	struct bpf_prog __rcu	*flow_dissector_prog;
+
 	/* Note : following structs are cache line aligned */
 #ifdef CONFIG_XFRM
 	struct netns_xfrm	xfrm;

include/net/sch_generic.h

@@ -19,6 +19,7 @@ struct Qdisc_ops;
 struct qdisc_walker;
 struct tcf_walker;
 struct module;
+struct bpf_flow_keys;
 
 typedef int tc_setup_cb_t(enum tc_setup_type type,
 			  void *type_data, void *cb_priv);
@@ -307,9 +308,14 @@ struct tcf_proto {
 };
 
 struct qdisc_skb_cb {
+	union {
+		struct {
 			unsigned int		pkt_len;
 			u16			slave_dev_queue_mapping;
 			u16			tc_classid;
+		};
+		struct bpf_flow_keys *flow_keys;
+	};
 #define QDISC_CB_PRIV_LEN 20
 	unsigned char		data[QDISC_CB_PRIV_LEN];
 };

include/uapi/linux/bpf.h

@@ -152,6 +152,7 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_LWT_SEG6LOCAL,
 	BPF_PROG_TYPE_LIRC_MODE2,
 	BPF_PROG_TYPE_SK_REUSEPORT,
+	BPF_PROG_TYPE_FLOW_DISSECTOR,
 };
 
 enum bpf_attach_type {
@@ -172,6 +173,7 @@ enum bpf_attach_type {
 	BPF_CGROUP_UDP4_SENDMSG,
 	BPF_CGROUP_UDP6_SENDMSG,
 	BPF_LIRC_MODE2,
+	BPF_FLOW_DISSECTOR,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -2333,6 +2335,7 @@ struct __sk_buff {
 	/* ... here. */
 
 	__u32 data_meta;
+	struct bpf_flow_keys *flow_keys;
 };
 
 struct bpf_tunnel_key {
@@ -2778,4 +2781,27 @@ enum bpf_task_fd_type {
 	BPF_FD_TYPE_URETPROBE,		/* filename + offset */
 };
 
+struct bpf_flow_keys {
+	__u16	nhoff;
+	__u16	thoff;
+	__u16	addr_proto;			/* ETH_P_* of valid addrs */
+	__u8	is_frag;
+	__u8	is_first_frag;
+	__u8	is_encap;
+	__u8	ip_proto;
+	__be16	n_proto;
+	__be16	sport;
+	__be16	dport;
+	union {
+		struct {
+			__be32	ipv4_src;
+			__be32	ipv4_dst;
+		};
+		struct {
+			__u32	ipv6_src[4];	/* in6_addr; network order */
+			__u32	ipv6_dst[4];	/* in6_addr; network order */
+		};
+	};
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */

kernel/bpf/syscall.c

@@ -1615,6 +1615,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 	case BPF_LIRC_MODE2:
 		ptype = BPF_PROG_TYPE_LIRC_MODE2;
 		break;
+	case BPF_FLOW_DISSECTOR:
+		ptype = BPF_PROG_TYPE_FLOW_DISSECTOR;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -1636,6 +1639,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 	case BPF_PROG_TYPE_LIRC_MODE2:
 		ret = lirc_prog_attach(attr, prog);
 		break;
+	case BPF_PROG_TYPE_FLOW_DISSECTOR:
+		ret = skb_flow_dissector_bpf_prog_attach(attr, prog);
+		break;
 	default:
 		ret = cgroup_bpf_prog_attach(attr, ptype, prog);
 	}
@@ -1688,6 +1694,8 @@ static int bpf_prog_detach(const union bpf_attr *attr)
 		return sockmap_get_from_fd(attr, BPF_PROG_TYPE_SK_SKB, NULL);
 	case BPF_LIRC_MODE2:
 		return lirc_prog_detach(attr);
+	case BPF_FLOW_DISSECTOR:
+		return skb_flow_dissector_bpf_prog_detach(attr);
 	default:
 		return -EINVAL;
 	}

kernel/bpf/verifier.c

@@ -261,6 +261,7 @@ static const char * const reg_type_str[] = {
 	[PTR_TO_PACKET]		= "pkt",
 	[PTR_TO_PACKET_META]	= "pkt_meta",
 	[PTR_TO_PACKET_END]	= "pkt_end",
+	[PTR_TO_FLOW_KEYS]	= "flow_keys",
 };
 
 static char slot_type_char[] = {
@@ -965,6 +966,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
 	case PTR_TO_PACKET:
 	case PTR_TO_PACKET_META:
 	case PTR_TO_PACKET_END:
+	case PTR_TO_FLOW_KEYS:
 	case CONST_PTR_TO_MAP:
 		return true;
 	default:
@@ -1238,6 +1240,7 @@ static bool may_access_direct_pkt_data(struct bpf_verifier_env *env,
 	case BPF_PROG_TYPE_LWT_XMIT:
 	case BPF_PROG_TYPE_SK_SKB:
 	case BPF_PROG_TYPE_SK_MSG:
+	case BPF_PROG_TYPE_FLOW_DISSECTOR:
 		if (meta)
 			return meta->pkt_access;
 
@@ -1321,6 +1324,18 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off,
 	return -EACCES;
 }
 
+static int check_flow_keys_access(struct bpf_verifier_env *env, int off,
+				  int size)
+{
+	if (size < 0 || off < 0 ||
+	    (u64)off + size > sizeof(struct bpf_flow_keys)) {
+		verbose(env, "invalid access to flow keys off=%d size=%d\n",
+			off, size);
+		return -EACCES;
+	}
+	return 0;
+}
+
 static bool __is_pointer_value(bool allow_ptr_leaks,
 			       const struct bpf_reg_state *reg)
 {
@@ -1422,6 +1437,9 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
 		 * right in front, treat it the very same way.
 		 */
 		return check_pkt_ptr_alignment(env, reg, off, size, strict);
+	case PTR_TO_FLOW_KEYS:
+		pointer_desc = "flow keys ";
+		break;
 	case PTR_TO_MAP_VALUE:
 		pointer_desc = "value ";
 		break;
@@ -1692,6 +1710,17 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 		err = check_packet_access(env, regno, off, size, false);
 		if (!err && t == BPF_READ && value_regno >= 0)
 			mark_reg_unknown(env, regs, value_regno);
+	} else if (reg->type == PTR_TO_FLOW_KEYS) {
+		if (t == BPF_WRITE && value_regno >= 0 &&
+		    is_pointer_value(env, value_regno)) {
+			verbose(env, "R%d leaks addr into flow keys\n",
+				value_regno);
+			return -EACCES;
+		}
+
+		err = check_flow_keys_access(env, off, size);
+		if (!err && t == BPF_READ && value_regno >= 0)
+			mark_reg_unknown(env, regs, value_regno);
 	} else {
 		verbose(env, "R%d invalid mem access '%s'\n", regno,
 			reg_type_str[reg->type]);
@@ -1839,6 +1868,8 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
 	case PTR_TO_PACKET_META:
 		return check_packet_access(env, regno, reg->off, access_size,
 					   zero_size_allowed);
+	case PTR_TO_FLOW_KEYS:
+		return check_flow_keys_access(env, reg->off, access_size);
 	case PTR_TO_MAP_VALUE:
 		return check_map_access(env, regno, reg->off, access_size,
 					zero_size_allowed);
@@ -4366,6 +4397,7 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
 	case PTR_TO_CTX:
 	case CONST_PTR_TO_MAP:
 	case PTR_TO_PACKET_END:
+	case PTR_TO_FLOW_KEYS:
 		/* Only valid matches are exact, which memcmp() above
 		 * would have accepted
 		 */

net/core/filter.c

@@ -5123,6 +5123,17 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	}
 }
 
+static const struct bpf_func_proto *
+flow_dissector_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
+{
+	switch (func_id) {
+	case BPF_FUNC_skb_load_bytes:
+		return &bpf_skb_load_bytes_proto;
+	default:
+		return bpf_base_func_proto(func_id);
+	}
+}
+
 static const struct bpf_func_proto *
 lwt_out_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -5241,6 +5252,10 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type
 		if (size != size_default)
 			return false;
 		break;
+	case bpf_ctx_range(struct __sk_buff, flow_keys):
+		if (size != sizeof(struct bpf_flow_keys *))
+			return false;
+		break;
 	default:
 		/* Only narrow read access allowed for now. */
 		if (type == BPF_WRITE) {
@@ -5266,6 +5281,7 @@ static bool sk_filter_is_valid_access(int off, int size,
 	case bpf_ctx_range(struct __sk_buff, data):
 	case bpf_ctx_range(struct __sk_buff, data_meta):
 	case bpf_ctx_range(struct __sk_buff, data_end):
+	case bpf_ctx_range(struct __sk_buff, flow_keys):
 	case bpf_ctx_range_till(struct __sk_buff, family, local_port):
 		return false;
 	}
@@ -5291,6 +5307,7 @@ static bool lwt_is_valid_access(int off, int size,
 	case bpf_ctx_range(struct __sk_buff, tc_classid):
 	case bpf_ctx_range_till(struct __sk_buff, family, local_port):
 	case bpf_ctx_range(struct __sk_buff, data_meta):
+	case bpf_ctx_range(struct __sk_buff, flow_keys):
 		return false;
 	}
 
@@ -5501,6 +5518,7 @@ static bool tc_cls_act_is_valid_access(int off, int size,
 	case bpf_ctx_range(struct __sk_buff, data_end):
 		info->reg_type = PTR_TO_PACKET_END;
 		break;
+	case bpf_ctx_range(struct __sk_buff, flow_keys):
 	case bpf_ctx_range_till(struct __sk_buff, family, local_port):
 		return false;
 	}
@@ -5702,6 +5720,7 @@ static bool sk_skb_is_valid_access(int off, int size,
 	switch (off) {
 	case bpf_ctx_range(struct __sk_buff, tc_classid):
 	case bpf_ctx_range(struct __sk_buff, data_meta):
+	case bpf_ctx_range(struct __sk_buff, flow_keys):
 		return false;
 	}
 
@@ -5761,6 +5780,39 @@ static bool sk_msg_is_valid_access(int off, int size,
 	return true;
 }
 
+static bool flow_dissector_is_valid_access(int off, int size,
+					   enum bpf_access_type type,
+					   const struct bpf_prog *prog,
+					   struct bpf_insn_access_aux *info)
+{
+	if (type == BPF_WRITE) {
+		switch (off) {
+		case bpf_ctx_range_till(struct __sk_buff, cb[0], cb[4]):
+			break;
+		default:
+			return false;
+		}
+	}
+
+	switch (off) {
+	case bpf_ctx_range(struct __sk_buff, data):
+		info->reg_type = PTR_TO_PACKET;
+		break;
+	case bpf_ctx_range(struct __sk_buff, data_end):
+		info->reg_type = PTR_TO_PACKET_END;
+		break;
+	case bpf_ctx_range(struct __sk_buff, flow_keys):
+		info->reg_type = PTR_TO_FLOW_KEYS;
+		break;
+	case bpf_ctx_range(struct __sk_buff, tc_classid):
+	case bpf_ctx_range(struct __sk_buff, data_meta):
+	case bpf_ctx_range_till(struct __sk_buff, family, local_port):
+		return false;
+	}
+
+	return bpf_skb_is_valid_access(off, size, type, prog, info);
+}
+
 static u32 bpf_convert_ctx_access(enum bpf_access_type type,
 				  const struct bpf_insn *si,
 				  struct bpf_insn *insn_buf,
@@ -6055,6 +6107,15 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
 				      bpf_target_off(struct sock_common,
 						     skc_num, 2, target_size));
 		break;
+
+	case offsetof(struct __sk_buff, flow_keys):
+		off  = si->off;
+		off -= offsetof(struct __sk_buff, flow_keys);
+		off += offsetof(struct sk_buff, cb);
+		off += offsetof(struct qdisc_skb_cb, flow_keys);
+		*insn++ = BPF_LDX_MEM(BPF_SIZEOF(void *), si->dst_reg,
+				      si->src_reg, off);
+		break;
 	}
 
 	return insn - insn_buf;
@@ -7018,6 +7079,15 @@ const struct bpf_verifier_ops sk_msg_verifier_ops = {
 const struct bpf_prog_ops sk_msg_prog_ops = {
 };
 
+const struct bpf_verifier_ops flow_dissector_verifier_ops = {
+	.get_func_proto		= flow_dissector_func_proto,
+	.is_valid_access	= flow_dissector_is_valid_access,
+	.convert_ctx_access	= bpf_convert_ctx_access,
+};
+
+const struct bpf_prog_ops flow_dissector_prog_ops = {
+};
+
 int sk_detach_filter(struct sock *sk)
 {
 	int ret = -ENOENT;

net/core/flow_dissector.c

@@ -25,6 +25,9 @@
 #include <net/flow_dissector.h>
 #include <scsi/fc/fc_fcoe.h>
 #include <uapi/linux/batadv_packet.h>
+#include <linux/bpf.h>
+
+static DEFINE_MUTEX(flow_dissector_mutex);
 
 static void dissector_set_key(struct flow_dissector *flow_dissector,
 			      enum flow_dissector_key_id key_id)
@@ -62,6 +65,44 @@ void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
 }
 EXPORT_SYMBOL(skb_flow_dissector_init);
 
+int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
+				       struct bpf_prog *prog)
+{
+	struct bpf_prog *attached;
+	struct net *net;
+
+	net = current->nsproxy->net_ns;
+	mutex_lock(&flow_dissector_mutex);
+	attached = rcu_dereference_protected(net->flow_dissector_prog,
+					     lockdep_is_held(&flow_dissector_mutex));
+	if (attached) {
+		/* Only one BPF program can be attached at a time */
+		mutex_unlock(&flow_dissector_mutex);
+		return -EEXIST;
+	}
+	rcu_assign_pointer(net->flow_dissector_prog, prog);
+	mutex_unlock(&flow_dissector_mutex);
+	return 0;
+}
+
+int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
+{
+	struct bpf_prog *attached;
+	struct net *net;
+
+	net = current->nsproxy->net_ns;
+	mutex_lock(&flow_dissector_mutex);
+	attached = rcu_dereference_protected(net->flow_dissector_prog,
+					     lockdep_is_held(&flow_dissector_mutex));
+	if (!attached) {
+		mutex_unlock(&flow_dissector_mutex);
+		return -ENOENT;
+	}
+	bpf_prog_put(attached);
+	RCU_INIT_POINTER(net->flow_dissector_prog, NULL);
+	mutex_unlock(&flow_dissector_mutex);
+	return 0;
+}
 /**
  * skb_flow_get_be16 - extract be16 entity
  * @skb: sk_buff to extract from
@@ -588,6 +629,60 @@ static bool skb_flow_dissect_allowed(int *num_hdrs)
 	return (*num_hdrs <= MAX_FLOW_DISSECT_HDRS);
 }
 
+static void __skb_flow_bpf_to_target(const struct bpf_flow_keys *flow_keys,
+				     struct flow_dissector *flow_dissector,
+				     void *target_container)
+{
+	struct flow_dissector_key_control *key_control;
+	struct flow_dissector_key_basic *key_basic;
+	struct flow_dissector_key_addrs *key_addrs;
+	struct flow_dissector_key_ports *key_ports;
+
+	key_control = skb_flow_dissector_target(flow_dissector,
+						FLOW_DISSECTOR_KEY_CONTROL,
+						target_container);
+	key_control->thoff = flow_keys->thoff;
+	if (flow_keys->is_frag)
+		key_control->flags |= FLOW_DIS_IS_FRAGMENT;
+	if (flow_keys->is_first_frag)
+		key_control->flags |= FLOW_DIS_FIRST_FRAG;
+	if (flow_keys->is_encap)
+		key_control->flags |= FLOW_DIS_ENCAPSULATION;
+
+	key_basic = skb_flow_dissector_target(flow_dissector,
+					      FLOW_DISSECTOR_KEY_BASIC,
+					      target_container);
+	key_basic->n_proto = flow_keys->n_proto;
+	key_basic->ip_proto = flow_keys->ip_proto;
+
+	if (flow_keys->addr_proto == ETH_P_IP &&
+	    dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_IPV4_ADDRS)) {
+		key_addrs = skb_flow_dissector_target(flow_dissector,
+						      FLOW_DISSECTOR_KEY_IPV4_ADDRS,
+						      target_container);
+		key_addrs->v4addrs.src = flow_keys->ipv4_src;
+		key_addrs->v4addrs.dst = flow_keys->ipv4_dst;
+		key_control->addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
+	} else if (flow_keys->addr_proto == ETH_P_IPV6 &&
+		   dissector_uses_key(flow_dissector,
+				      FLOW_DISSECTOR_KEY_IPV6_ADDRS)) {
+		key_addrs = skb_flow_dissector_target(flow_dissector,
+						      FLOW_DISSECTOR_KEY_IPV6_ADDRS,
+						      target_container);
+		memcpy(&key_addrs->v6addrs, &flow_keys->ipv6_src,
+		       sizeof(key_addrs->v6addrs));
+		key_control->addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
+	}
+
+	if (dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_PORTS)) {
+		key_ports = skb_flow_dissector_target(flow_dissector,
+						      FLOW_DISSECTOR_KEY_PORTS,
+						      target_container);
+		key_ports->src = flow_keys->sport;
+		key_ports->dst = flow_keys->dport;
+	}
+}
+
 /**
  * __skb_flow_dissect - extract the flow_keys struct and return it
  * @skb: sk_buff to extract the flow from, can be NULL if the rest are specified
@@ -619,6 +714,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 	struct flow_dissector_key_vlan *key_vlan;
 	enum flow_dissect_ret fdret;
 	enum flow_dissector_key_id dissector_vlan = FLOW_DISSECTOR_KEY_MAX;
+	struct bpf_prog *attached;
 	int num_hdrs = 0;
 	u8 ip_proto = 0;
 	bool ret;
@@ -658,6 +754,44 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 					      FLOW_DISSECTOR_KEY_BASIC,
 					      target_container);
 
+	rcu_read_lock();
+	attached = skb ? rcu_dereference(dev_net(skb->dev)->flow_dissector_prog)
+		       : NULL;
+	if (attached) {
+		/* Note that even though the const qualifier is discarded
+		 * throughout the execution of the BPF program, all changes(the
+		 * control block) are reverted after the BPF program returns.
+		 * Therefore, __skb_flow_dissect does not alter the skb.
+		 */
+		struct bpf_flow_keys flow_keys = {};
+		struct bpf_skb_data_end cb_saved;
+		struct bpf_skb_data_end *cb;
+		u32 result;
+
+		cb = (struct bpf_skb_data_end *)skb->cb;
+
+		/* Save Control Block */
+		memcpy(&cb_saved, cb, sizeof(cb_saved));
+		memset(cb, 0, sizeof(cb_saved));
+
+		/* Pass parameters to the BPF program */
+		cb->qdisc_cb.flow_keys = &flow_keys;
+		flow_keys.nhoff = nhoff;
+
+		bpf_compute_data_pointers((struct sk_buff *)skb);
+		result = BPF_PROG_RUN(attached, skb);
+
+		/* Restore state */
+		memcpy(cb, &cb_saved, sizeof(cb_saved));
+
+		__skb_flow_bpf_to_target(&flow_keys, flow_dissector,
+					 target_container);
+		key_control->thoff = min_t(u16, key_control->thoff, skb->len);
+		rcu_read_unlock();
+		return result == BPF_OK;
+	}
+	rcu_read_unlock();
+
 	if (dissector_uses_key(flow_dissector,
 			       FLOW_DISSECTOR_KEY_ETH_ADDRS)) {
 		struct ethhdr *eth = eth_hdr(skb);