From 953af8e3acb68d2db11937cec3bc5da31de5c12e Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Mon, 23 Oct 2023 20:22:08 +0100 Subject: net/tcp: Ignore specific ICMPs for TCP-AO connections MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Francesco Ruggeri Co-developed-by: Salam Noureddine Signed-off-by: Salam Noureddine Signed-off-by: Dmitry Safonov Acked-by: David Ahern Signed-off-by: David S. Miller --- include/net/tcp_ao.h | 11 ++++++++- include/uapi/linux/snmp.h | 1 + include/uapi/linux/tcp.h | 4 +++- net/ipv4/proc.c | 1 + net/ipv4/tcp_ao.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++ net/ipv4/tcp_ipv4.c | 7 ++++++ net/ipv6/tcp_ipv6.c | 7 ++++++ 7 files changed, 87 insertions(+), 2 deletions(-) diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h index 4da6e3657913..a9d38b9e8bcb 100644 --- a/include/net/tcp_ao.h +++ b/include/net/tcp_ao.h @@ -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) diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h index 3d5ea841bffe..a0819c6a5988 100644 --- a/include/uapi/linux/snmp.h +++ b/include/uapi/linux/snmp.h @@ -301,6 +301,7 @@ 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 9c48964849d1..d8b2ea23f12a 100644 --- a/include/uapi/linux/tcp.h +++ b/include/uapi/linux/tcp.h @@ -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, ...) */ diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c index f5b37ebc18c0..5f4654ebff48 100644 --- a/net/ipv4/proc.c +++ b/net/ipv4/proc.c @@ -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 }; diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c index f76fcb93499d..223af5c9eaf3 100644 --- a/net/ipv4/tcp_ao.c +++ b/net/ipv4/tcp_ao.c @@ -15,6 +15,7 @@ #include #include +#include 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 @@ clear_hash: 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) diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index bdec99707028..8f98c58e2689 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -494,6 +494,8 @@ 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, AF_INET, type, code); inet_twsk_put(inet_twsk(sk)); return 0; } @@ -507,6 +509,11 @@ int tcp_v4_err(struct sk_buff *skb, u32 info) return 0; } + if (tcp_ao_ignore_icmp(sk, AF_INET, type, code)) { + sock_put(sk); + return 0; + } + bh_lock_sock(sk); /* If too many ICMPs get dropped on busy * servers this needs to be solved differently. diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 4dcbc13e9ec8..fa7050579e9a 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -396,6 +396,8 @@ 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, AF_INET6, type, code); inet_twsk_put(inet_twsk(sk)); return 0; } @@ -406,6 +408,11 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt, return 0; } + if (tcp_ao_ignore_icmp(sk, AF_INET6, type, code)) { + sock_put(sk); + return 0; + } + bh_lock_sock(sk); if (sock_owned_by_user(sk) && type != ICMPV6_PKT_TOOBIG) __NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS); -- cgit