Commit 953af8e3 authored by Dmitry Safonov's avatar Dmitry Safonov Committed by David S. Miller
Browse files

net/tcp: Ignore specific ICMPs for TCP-AO connections 



Similarly to IPsec, RFC5925 prescribes:
  ">> A TCP-AO implementation MUST default to ignore incoming ICMPv4
  messages of Type 3 (destination unreachable), Codes 2-4 (protocol
  unreachable, port unreachable, and fragmentation needed -- ’hard
  errors’), and ICMPv6 Type 1 (destination unreachable), Code 1
  (administratively prohibited) and Code 4 (port unreachable) intended
  for connections in synchronized states (ESTABLISHED, FIN-WAIT-1, FIN-
  WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT) that match MKTs."

A selftest (later in patch series) verifies that this attack is not
possible in this TCP-AO implementation.

Co-developed-by: default avatarFrancesco Ruggeri <fruggeri@arista.com>
Signed-off-by: default avatarFrancesco Ruggeri <fruggeri@arista.com>
Co-developed-by: default avatarSalam Noureddine <noureddine@arista.com>
Signed-off-by: default avatarSalam Noureddine <noureddine@arista.com>
Signed-off-by: default avatarDmitry Safonov <dima@arista.com>
Acked-by: default avatarDavid Ahern <dsahern@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2717b5ad

include/net/tcp_ao.h

+10 −1
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ struct tcp_ao_counters { 
	atomic64_t	pkt_bad;

	atomic64_t	key_not_found;

	atomic64_t	ao_required;

	atomic64_t	dropped_icmp;

};



struct tcp_ao_key {
@@ -92,7 +93,8 @@ struct tcp_ao_info { 
	struct tcp_ao_key	*rnext_key;

	struct tcp_ao_counters	counters;

	u32			ao_required	:1,

				__unused	:31;

				accept_icmps	:1,

				__unused	:30;

	__be32			lisn;

	__be32			risn;

	/* Sequence Number Extension (SNE) are upper 4 bytes for SEQ,
@@ -191,6 +193,7 @@ int tcp_ao_calc_traffic_key(struct tcp_ao_key *mkt, u8 *key, void *ctx, 
			    unsigned int len, struct tcp_sigpool *hp);

void tcp_ao_destroy_sock(struct sock *sk, bool twsk);

void tcp_ao_time_wait(struct tcp_timewait_sock *tcptw, struct tcp_sock *tp);

bool tcp_ao_ignore_icmp(const struct sock *sk, int family, int type, int code);

enum skb_drop_reason tcp_inbound_ao_hash(struct sock *sk,

			const struct sk_buff *skb, unsigned short int family,

			const struct request_sock *req,
@@ -274,6 +277,12 @@ static inline void tcp_ao_syncookie(struct sock *sk, const struct sk_buff *skb, 
{

}



static inline bool tcp_ao_ignore_icmp(const struct sock *sk, int family,

				      int type, int code)

{

	return false;

}



static inline enum skb_drop_reason tcp_inbound_ao_hash(struct sock *sk,

		const struct sk_buff *skb, unsigned short int family,

		const struct request_sock *req, const struct tcp_ao_hdr *aoh)

include/uapi/linux/snmp.h

+1 −0
Original line number Diff line number Diff line
@@ -301,6 +301,7 @@ enum 
	LINUX_MIB_TCPAOBAD,			/* TCPAOBad */

	LINUX_MIB_TCPAOKEYNOTFOUND,		/* TCPAOKeyNotFound */

	LINUX_MIB_TCPAOGOOD,			/* TCPAOGood */

	LINUX_MIB_TCPAODROPPEDICMPS,		/* TCPAODroppedIcmps */

	__LINUX_MIB_MAX

};

include/uapi/linux/tcp.h

+3 −1
Original line number Diff line number Diff line
@@ -405,7 +405,8 @@ struct tcp_ao_info_opt { /* setsockopt(TCP_AO_INFO) */ 
		set_rnext	:1,	/* corresponding ::rnext */

		ao_required	:1,	/* don't accept non-AO connects */

		set_counters	:1,	/* set/clear ::pkt_* counters */

		reserved	:28;	/* must be 0 */

		accept_icmps	:1,	/* accept incoming ICMPs */

		reserved	:27;	/* must be 0 */

	__u16	reserved2;		/* padding, must be 0 */

	__u8	current_key;		/* KeyID to set as Current_key */

	__u8	rnext;			/* KeyID to set as Rnext_key */
@@ -413,6 +414,7 @@ struct tcp_ao_info_opt { /* setsockopt(TCP_AO_INFO) */ 
	__u64	pkt_bad;		/* failed verification */

	__u64	pkt_key_not_found;	/* could not find a key to verify */

	__u64	pkt_ao_required;	/* segments missing TCP-AO sign */

	__u64	pkt_dropped_icmp;	/* ICMPs that were ignored */

} __attribute__((aligned(8)));



/* setsockopt(fd, IPPROTO_TCP, TCP_ZEROCOPY_RECEIVE, ...) */

net/ipv4/proc.c

+1 −0
Original line number Diff line number Diff line
@@ -303,6 +303,7 @@ static const struct snmp_mib snmp4_net_list[] = { 
	SNMP_MIB_ITEM("TCPAOBad", LINUX_MIB_TCPAOBAD),

	SNMP_MIB_ITEM("TCPAOKeyNotFound", LINUX_MIB_TCPAOKEYNOTFOUND),

	SNMP_MIB_ITEM("TCPAOGood", LINUX_MIB_TCPAOGOOD),

	SNMP_MIB_ITEM("TCPAODroppedIcmps", LINUX_MIB_TCPAODROPPEDICMPS),

	SNMP_MIB_SENTINEL

};

net/ipv4/tcp_ao.c

+58 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 


#include <net/tcp.h>

#include <net/ipv6.h>

#include <net/icmp.h>



int tcp_ao_calc_traffic_key(struct tcp_ao_key *mkt, u8 *key, void *ctx,

			    unsigned int len, struct tcp_sigpool *hp)
@@ -44,6 +45,60 @@ int tcp_ao_calc_traffic_key(struct tcp_ao_key *mkt, u8 *key, void *ctx, 
	return 1;

}



bool tcp_ao_ignore_icmp(const struct sock *sk, int family, int type, int code)

{

	bool ignore_icmp = false;

	struct tcp_ao_info *ao;



	/* RFC5925, 7.8:

	 * >> A TCP-AO implementation MUST default to ignore incoming ICMPv4

	 * messages of Type 3 (destination unreachable), Codes 2-4 (protocol

	 * unreachable, port unreachable, and fragmentation needed -- ’hard

	 * errors’), and ICMPv6 Type 1 (destination unreachable), Code 1

	 * (administratively prohibited) and Code 4 (port unreachable) intended

	 * for connections in synchronized states (ESTABLISHED, FIN-WAIT-1, FIN-

	 * WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT) that match MKTs.

	 */

	if (family == AF_INET) {

		if (type != ICMP_DEST_UNREACH)

			return false;

		if (code < ICMP_PROT_UNREACH || code > ICMP_FRAG_NEEDED)

			return false;

	} else {

		if (type != ICMPV6_DEST_UNREACH)

			return false;

		if (code != ICMPV6_ADM_PROHIBITED && code != ICMPV6_PORT_UNREACH)

			return false;

	}



	rcu_read_lock();

	switch (sk->sk_state) {

	case TCP_TIME_WAIT:

		ao = rcu_dereference(tcp_twsk(sk)->ao_info);

		break;

	case TCP_SYN_SENT:

	case TCP_SYN_RECV:

	case TCP_LISTEN:

	case TCP_NEW_SYN_RECV:

		/* RFC5925 specifies to ignore ICMPs *only* on connections

		 * in synchronized states.

		 */

		rcu_read_unlock();

		return false;

	default:

		ao = rcu_dereference(tcp_sk(sk)->ao_info);

	}



	if (ao && !ao->accept_icmps) {

		ignore_icmp = true;

		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPAODROPPEDICMPS);

		atomic64_inc(&ao->counters.dropped_icmp);

	}

	rcu_read_unlock();



	return ignore_icmp;

}



/* Optimized version of tcp_ao_do_lookup(): only for sockets for which

 * it's known that the keys in ao_info are matching peer's

 * family/address/VRF/etc.
@@ -1086,6 +1141,7 @@ int tcp_ao_copy_all_matching(const struct sock *sk, struct sock *newsk, 
	new_ao->lisn = htonl(tcp_rsk(req)->snt_isn);

	new_ao->risn = htonl(tcp_rsk(req)->rcv_isn);

	new_ao->ao_required = ao->ao_required;

	new_ao->accept_icmps = ao->accept_icmps;



	if (family == AF_INET) {

		addr = (union tcp_ao_addr *)&newsk->sk_daddr;
@@ -1792,9 +1848,11 @@ static int tcp_ao_info_cmd(struct sock *sk, unsigned short int family, 
		atomic64_set(&ao_info->counters.pkt_bad, cmd.pkt_bad);

		atomic64_set(&ao_info->counters.key_not_found, cmd.pkt_key_not_found);

		atomic64_set(&ao_info->counters.ao_required, cmd.pkt_ao_required);

		atomic64_set(&ao_info->counters.dropped_icmp, cmd.pkt_dropped_icmp);

	}



	ao_info->ao_required = cmd.ao_required;

	ao_info->accept_icmps = cmd.accept_icmps;

	if (new_current)

		WRITE_ONCE(ao_info->current_key, new_current);

	if (new_rnext)