From 0a3a809089eb1d4a0a2fd0c16b520d603988c859 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Mon, 23 Oct 2023 20:22:04 +0100 Subject: net/tcp: Verify inbound TCP-AO signed segments Now there is a common function to verify signature on TCP segments: tcp_inbound_hash(). It has checks for all possible cross-interactions with MD5 signs as well as with unsigned segments. The rules from RFC5925 are: (1) Any TCP segment can have at max only one signature. (2) TCP connections can't switch between using TCP-MD5 and TCP-AO. (3) TCP-AO connections can't stop using AO, as well as unsigned connections can't suddenly start using AO. 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 --- net/ipv4/tcp.c | 39 +++------------ net/ipv4/tcp_ao.c | 142 ++++++++++++++++++++++++++++++++++++++++++++++++++++ net/ipv4/tcp_ipv4.c | 10 ++-- net/ipv6/tcp_ao.c | 9 ++-- net/ipv6/tcp_ipv6.c | 11 ++-- 5 files changed, 166 insertions(+), 45 deletions(-) (limited to 'net') diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 369e2a41bc1b..eb71212a09d8 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -4375,42 +4375,23 @@ EXPORT_SYMBOL(tcp_md5_hash_key); enum skb_drop_reason tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb, const void *saddr, const void *daddr, - int family, int dif, int sdif) + int family, int l3index, const __u8 *hash_location) { - /* - * This gets called for each TCP segment that arrives - * so we want to be efficient. + /* This gets called for each TCP segment that has TCP-MD5 option. * We have 3 drop cases: * o No MD5 hash and one expected. * o MD5 hash and we're not expecting one. * o MD5 hash and its wrong. */ - const __u8 *hash_location = NULL; - struct tcp_md5sig_key *hash_expected; const struct tcphdr *th = tcp_hdr(skb); const struct tcp_sock *tp = tcp_sk(sk); - int genhash, l3index; + struct tcp_md5sig_key *key; u8 newhash[16]; + int genhash; - /* sdif set, means packet ingressed via a device - * in an L3 domain and dif is set to the l3mdev - */ - l3index = sdif ? dif : 0; - - hash_expected = tcp_md5_do_lookup(sk, l3index, saddr, family); - if (tcp_parse_auth_options(th, &hash_location, NULL)) - return SKB_DROP_REASON_TCP_AUTH_HDR; - - /* We've parsed the options - do we have a hash? */ - if (!hash_expected && !hash_location) - return SKB_NOT_DROPPED_YET; + key = tcp_md5_do_lookup(sk, l3index, saddr, family); - if (hash_expected && !hash_location) { - NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND); - return SKB_DROP_REASON_TCP_MD5NOTFOUND; - } - - if (!hash_expected && hash_location) { + if (!key && hash_location) { NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED); return SKB_DROP_REASON_TCP_MD5UNEXPECTED; } @@ -4420,14 +4401,10 @@ tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb, * IPv4-mapped case. */ if (family == AF_INET) - genhash = tcp_v4_md5_hash_skb(newhash, - hash_expected, - NULL, skb); + genhash = tcp_v4_md5_hash_skb(newhash, key, NULL, skb); else - genhash = tp->af_specific->calc_md5_hash(newhash, - hash_expected, + genhash = tp->af_specific->calc_md5_hash(newhash, key, NULL, skb); - if (genhash || memcmp(hash_location, newhash, 16) != 0) { NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5FAILURE); if (family == AF_INET) { diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c index de3710758d55..6c5815713b73 100644 --- a/net/ipv4/tcp_ao.c +++ b/net/ipv4/tcp_ao.c @@ -761,6 +761,148 @@ void tcp_ao_syncookie(struct sock *sk, const struct sk_buff *skb, treq->maclen = tcp_ao_maclen(key); } +static enum skb_drop_reason +tcp_ao_verify_hash(const struct sock *sk, const struct sk_buff *skb, + unsigned short int family, struct tcp_ao_info *info, + const struct tcp_ao_hdr *aoh, struct tcp_ao_key *key, + u8 *traffic_key, u8 *phash, u32 sne) +{ + u8 maclen = aoh->length - sizeof(struct tcp_ao_hdr); + const struct tcphdr *th = tcp_hdr(skb); + void *hash_buf = NULL; + + if (maclen != tcp_ao_maclen(key)) + return SKB_DROP_REASON_TCP_AOFAILURE; + + hash_buf = kmalloc(tcp_ao_digest_size(key), GFP_ATOMIC); + if (!hash_buf) + return SKB_DROP_REASON_NOT_SPECIFIED; + + /* XXX: make it per-AF callback? */ + tcp_ao_hash_skb(family, hash_buf, key, sk, skb, traffic_key, + (phash - (u8 *)th), sne); + if (memcmp(phash, hash_buf, maclen)) { + kfree(hash_buf); + return SKB_DROP_REASON_TCP_AOFAILURE; + } + kfree(hash_buf); + return SKB_NOT_DROPPED_YET; +} + +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) +{ + const struct tcphdr *th = tcp_hdr(skb); + u8 *phash = (u8 *)(aoh + 1); /* hash goes just after the header */ + struct tcp_ao_info *info; + enum skb_drop_reason ret; + struct tcp_ao_key *key; + __be32 sisn, disn; + u8 *traffic_key; + u32 sne = 0; + + info = rcu_dereference(tcp_sk(sk)->ao_info); + if (!info) + return SKB_DROP_REASON_TCP_AOUNEXPECTED; + + if (unlikely(th->syn)) { + sisn = th->seq; + disn = 0; + } + + /* Fast-path */ + if (likely((1 << sk->sk_state) & TCP_AO_ESTABLISHED)) { + enum skb_drop_reason err; + struct tcp_ao_key *current_key; + + /* Check if this socket's rnext_key matches the keyid in the + * packet. If not we lookup the key based on the keyid + * matching the rcvid in the mkt. + */ + key = READ_ONCE(info->rnext_key); + if (key->rcvid != aoh->keyid) { + key = tcp_ao_established_key(info, -1, aoh->keyid); + if (!key) + goto key_not_found; + } + + /* Delayed retransmitted SYN */ + if (unlikely(th->syn && !th->ack)) + goto verify_hash; + + sne = 0; + /* Established socket, traffic key are cached */ + traffic_key = rcv_other_key(key); + err = tcp_ao_verify_hash(sk, skb, family, info, aoh, key, + traffic_key, phash, sne); + if (err) + return err; + current_key = READ_ONCE(info->current_key); + /* Key rotation: the peer asks us to use new key (RNext) */ + if (unlikely(aoh->rnext_keyid != current_key->sndid)) { + /* If the key is not found we do nothing. */ + key = tcp_ao_established_key(info, aoh->rnext_keyid, -1); + if (key) + /* pairs with tcp_ao_del_cmd */ + WRITE_ONCE(info->current_key, key); + } + return SKB_NOT_DROPPED_YET; + } + + /* Lookup key based on peer address and keyid. + * current_key and rnext_key must not be used on tcp listen + * sockets as otherwise: + * - request sockets would race on those key pointers + * - tcp_ao_del_cmd() allows async key removal + */ + key = tcp_ao_inbound_lookup(family, sk, skb, -1, aoh->keyid); + if (!key) + goto key_not_found; + + if (th->syn && !th->ack) + goto verify_hash; + + if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV)) { + /* Make the initial syn the likely case here */ + if (unlikely(req)) { + sne = 0; + sisn = htonl(tcp_rsk(req)->rcv_isn); + disn = htonl(tcp_rsk(req)->snt_isn); + } else if (unlikely(th->ack && !th->syn)) { + /* Possible syncookie packet */ + sisn = htonl(ntohl(th->seq) - 1); + disn = htonl(ntohl(th->ack_seq) - 1); + sne = 0; + } else if (unlikely(!th->syn)) { + /* no way to figure out initial sisn/disn - drop */ + return SKB_DROP_REASON_TCP_FLAGS; + } + } else if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { + disn = info->lisn; + if (th->syn || th->rst) + sisn = th->seq; + else + sisn = info->risn; + } else { + WARN_ONCE(1, "TCP-AO: Unexpected sk_state %d", sk->sk_state); + return SKB_DROP_REASON_TCP_AOFAILURE; + } +verify_hash: + traffic_key = kmalloc(tcp_ao_digest_size(key), GFP_ATOMIC); + if (!traffic_key) + return SKB_DROP_REASON_NOT_SPECIFIED; + tcp_ao_calc_key_skb(key, traffic_key, skb, sisn, disn, family); + ret = tcp_ao_verify_hash(sk, skb, family, info, aoh, key, + traffic_key, phash, sne); + kfree(traffic_key); + return ret; + +key_not_found: + return SKB_DROP_REASON_TCP_AOKEYNOTFOUND; +} + static int tcp_ao_cache_traffic_keys(const struct sock *sk, struct tcp_ao_info *ao, struct tcp_ao_key *ao_key) diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index bdf0224ae827..f39ccefa78dc 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -2204,9 +2204,9 @@ process: if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb)) drop_reason = SKB_DROP_REASON_XFRM_POLICY; else - drop_reason = tcp_inbound_md5_hash(sk, skb, - &iph->saddr, &iph->daddr, - AF_INET, dif, sdif); + drop_reason = tcp_inbound_hash(sk, req, skb, + &iph->saddr, &iph->daddr, + AF_INET, dif, sdif); if (unlikely(drop_reason)) { sk_drops_add(sk, skb); reqsk_put(req); @@ -2283,8 +2283,8 @@ process: goto discard_and_relse; } - drop_reason = tcp_inbound_md5_hash(sk, skb, &iph->saddr, - &iph->daddr, AF_INET, dif, sdif); + drop_reason = tcp_inbound_hash(sk, NULL, skb, &iph->saddr, &iph->daddr, + AF_INET, dif, sdif); if (drop_reason) goto discard_and_relse; diff --git a/net/ipv6/tcp_ao.c b/net/ipv6/tcp_ao.c index 99753e12c08c..8b04611c9078 100644 --- a/net/ipv6/tcp_ao.c +++ b/net/ipv6/tcp_ao.c @@ -53,11 +53,12 @@ int tcp_v6_ao_calc_key_skb(struct tcp_ao_key *mkt, u8 *key, const struct sk_buff *skb, __be32 sisn, __be32 disn) { - const struct ipv6hdr *iph = ipv6_hdr(skb); - const struct tcphdr *th = tcp_hdr(skb); + const struct ipv6hdr *iph = ipv6_hdr(skb); + const struct tcphdr *th = tcp_hdr(skb); - return tcp_v6_ao_calc_key(mkt, key, &iph->saddr, &iph->daddr, - th->source, th->dest, sisn, disn); + return tcp_v6_ao_calc_key(mkt, key, &iph->saddr, + &iph->daddr, th->source, + th->dest, sisn, disn); } int tcp_v6_ao_calc_key_sk(struct tcp_ao_key *mkt, u8 *key, diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 8c5c96187a72..d2724383d263 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1785,9 +1785,9 @@ process: if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb)) drop_reason = SKB_DROP_REASON_XFRM_POLICY; else - drop_reason = tcp_inbound_md5_hash(sk, skb, - &hdr->saddr, &hdr->daddr, - AF_INET6, dif, sdif); + drop_reason = tcp_inbound_hash(sk, req, skb, + &hdr->saddr, &hdr->daddr, + AF_INET6, dif, sdif); if (drop_reason) { sk_drops_add(sk, skb); reqsk_put(req); @@ -1861,8 +1861,8 @@ process: goto discard_and_relse; } - drop_reason = tcp_inbound_md5_hash(sk, skb, &hdr->saddr, &hdr->daddr, - AF_INET6, dif, sdif); + drop_reason = tcp_inbound_hash(sk, NULL, skb, &hdr->saddr, &hdr->daddr, + AF_INET6, dif, sdif); if (drop_reason) goto discard_and_relse; @@ -2089,6 +2089,7 @@ static const struct tcp_sock_af_ops tcp_sock_ipv6_mapped_specific = { .ao_lookup = tcp_v6_ao_lookup, .calc_ao_hash = tcp_v4_ao_hash_skb, .ao_parse = tcp_v6_parse_ao, + .ao_calc_key_sk = tcp_v4_ao_calc_key_sk, #endif }; #endif -- cgit