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: Francesco Ruggeri <fruggeri@xxxxxxxxxx> Signed-off-by: Francesco Ruggeri <fruggeri@xxxxxxxxxx> Co-developed-by: Salam Noureddine <noureddine@xxxxxxxxxx> Signed-off-by: Salam Noureddine <noureddine@xxxxxxxxxx> Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx> --- include/net/tcp_ao.h | 9 +++++ include/uapi/linux/snmp.h | 1 + include/uapi/linux/tcp.h | 1 + net/ipv4/proc.c | 1 + net/ipv4/tcp_ao.c | 70 ++++++++++++++++++++++++++++++++++++++- net/ipv4/tcp_ipv4.c | 5 +++ net/ipv6/tcp_ipv6.c | 4 +++ 7 files changed, 90 insertions(+), 1 deletion(-) diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h index e99c8f300a5a..743a910ba508 100644 --- a/include/net/tcp_ao.h +++ b/include/net/tcp_ao.h @@ -25,6 +25,7 @@ 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 { @@ -77,6 +78,9 @@ static inline unsigned int tcp_ao_digest_size(struct tcp_ao_key *key) return key->digest_size; } +/* bits in 'ao_flags' */ +#define AO_ACCEPT_ICMPS BIT(0) + struct tcp_ao_info { struct hlist_head head; struct rcu_head rcu; @@ -169,6 +173,7 @@ u32 tcp_ao_compute_sne(u32 sne, u32 seq, u32 new_seq); void tcp_ao_time_wait(struct tcp_timewait_sock *tcptw, struct tcp_sock *tp); int tcp_ao_cache_traffic_keys(const struct sock *sk, struct tcp_ao_info *ao, struct tcp_ao_key *ao_key); +bool tcp_ao_ignore_icmp(struct sock *sk, 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, @@ -239,6 +244,10 @@ void tcp_ao_connect_init(struct sock *sk); #else /* CONFIG_TCP_AO */ +static inline bool tcp_ao_ignore_icmp(struct sock *sk, 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) diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h index f09119db8b40..bc7655394e9a 100644 --- a/include/uapi/linux/snmp.h +++ b/include/uapi/linux/snmp.h @@ -296,6 +296,7 @@ enum LINUX_MIB_TCPAOBAD, /* TCPAOBad */ LINUX_MIB_TCPAOKEYNOTFOUND, /* TCPAOKeyNotFound */ LINUX_MIB_TCPAOGOOD, /* TCPAOGood */ + LINUX_MIB_TCPAODROPPEDICMPS, /* TCPAODroppedIcmps */ __LINUX_MIB_MAX }; diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h index 5369458ae89f..508bedbc6ad8 100644 --- a/include/uapi/linux/tcp.h +++ b/include/uapi/linux/tcp.h @@ -349,6 +349,7 @@ struct tcp_diag_md5sig { #define TCP_AO_CMDF_CURR (1 << 0) /* Only checks field sndid */ #define TCP_AO_CMDF_NEXT (1 << 1) /* Only checks field rcvid */ +#define TCP_AO_CMDF_ACCEPT_ICMP (1 << 2) /* Accept incoming ICMPs */ struct tcp_ao { /* setsockopt(TCP_AO) */ struct __kernel_sockaddr_storage tcpa_addr; diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c index 1b5a078adcf1..ccfb7f51e82f 100644 --- a/net/ipv4/proc.c +++ b/net/ipv4/proc.c @@ -301,6 +301,7 @@ 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 }; diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c index 700e9a8bc983..5fb36863810d 100644 --- a/net/ipv4/tcp_ao.c +++ b/net/ipv4/tcp_ao.c @@ -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) @@ -52,6 +53,63 @@ int tcp_ao_calc_traffic_key(struct tcp_ao_key *mkt, u8 *key, void *ctx, return 1; } +bool tcp_ao_ignore_icmp(struct sock *sk, int type, int code) +{ + struct tcp_ao_info *ao; + bool ignore_icmp = false; + + /* 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 (sk->sk_family == AF_INET) { + if (type != ICMP_DEST_UNREACH) + return false; + if (code < ICMP_PROT_UNREACH || code > ICMP_FRAG_NEEDED) + return false; + } else if (sk->sk_family == AF_INET6) { + if (type != ICMPV6_DEST_UNREACH) + return false; + if (code != ICMPV6_ADM_PROHIBITED && code != ICMPV6_PORT_UNREACH) + return false; + } else { + WARN_ON_ONCE(1); + 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->ao_flags & 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; +} + struct tcp_ao_key *tcp_ao_do_lookup_keyid(struct tcp_ao_info *ao, int sndid, int rcvid) { @@ -1399,7 +1457,7 @@ static inline bool tcp_ao_mkt_overlap_v6(struct tcp_ao *cmd, #define TCP_AO_KEYF_ALL (0) #define TCP_AO_CMDF_ADDMOD_VALID \ - (TCP_AO_CMDF_CURR | TCP_AO_CMDF_NEXT) + (TCP_AO_CMDF_CURR | TCP_AO_CMDF_NEXT | TCP_AO_CMDF_ACCEPT_ICMP) #define TCP_AO_CMDF_DEL_VALID \ (TCP_AO_CMDF_CURR | TCP_AO_CMDF_NEXT) @@ -1482,6 +1540,11 @@ static int tcp_ao_add_cmd(struct sock *sk, unsigned short int family, atomic64_set(&key->pkt_good, 0); atomic64_set(&key->pkt_bad, 0); + if (cmd.tcpa_flags & TCP_AO_CMDF_ACCEPT_ICMP) + ao_info->ao_flags |= AO_ACCEPT_ICMPS; + else + ao_info->ao_flags &= ~AO_ACCEPT_ICMPS; + ret = tcp_ao_parse_crypto(&cmd, key); if (ret < 0) goto err_free_sock; @@ -1640,6 +1703,11 @@ static int tcp_ao_mod_cmd(struct sock *sk, unsigned short int family, if (!ao_info) return -ENOENT; /* TODO: make tcp_ao_current_rnext() and flags set atomic */ + if (cmd.tcpa_flags & TCP_AO_CMDF_ACCEPT_ICMP) + ao_info->ao_flags |= AO_ACCEPT_ICMPS; + else + ao_info->ao_flags &= ~AO_ACCEPT_ICMPS; + return tcp_ao_current_rnext(sk, cmd.tcpa_flags, cmd.tcpa_current, cmd.tcpa_rnext); } diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index ca4c6be886b7..372fbca343af 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -484,6 +484,8 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) return -ENOENT; } if (sk->sk_state == TCP_TIME_WAIT) { + /* To increase the counter of ignored icmps for TCP-AO */ + tcp_ao_ignore_icmp(sk, type, code); inet_twsk_put(inet_twsk(sk)); return 0; } @@ -498,6 +500,9 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) } bh_lock_sock(sk); + if (tcp_ao_ignore_icmp(sk, type, code)) + goto out; + /* If too many ICMPs get dropped on busy * servers this needs to be solved differently. * We do take care of PMTU discovery (RFC1191) special case : diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 8a27408549cd..78994d1cbc45 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -399,6 +399,8 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt, } if (sk->sk_state == TCP_TIME_WAIT) { + /* To increase the counter of ignored icmps for TCP-AO */ + tcp_ao_ignore_icmp(sk, type, code); inet_twsk_put(inet_twsk(sk)); return 0; } @@ -410,6 +412,8 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt, } bh_lock_sock(sk); + if (tcp_ao_ignore_icmp(sk, type, code)) + goto out; if (sock_owned_by_user(sk) && type != ICMPV6_PKT_TOOBIG) __NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS); -- 2.37.2