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: Francesco Ruggeri <fruggeri@arista.com>
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Co-developed-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index 4da6e36579133876402ffb2b75eca2e6f24c8f19..a9d38b9e8bcbf801082b9d6c266fc379a688df8b 100644 (file)
--- 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 3d5ea841bffe56d1ab9d441aee9a5e0767c40c35..a0819c6a5988fc97b14fc23cac3911e70a14cbff 100644 (file)
--- 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 9c48964849d1b34655a6446c637cf6d6ad302e2f..d8b2ea23f12a14266bd134c8c53c9f0ea4a843bf 100644 (file)
--- 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 f5b37ebc18c031a873f21601c4701fe42a7d0b34..5f4654ebff487494b6afbaa69174df4c004395dc 100644 (file)
--- 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 f76fcb93499d3bd377abe18961d99f612773622b..223af5c9eaf359a8a0e40f786fc1e570376b7bef 100644 (file)
--- 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, 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 bdec99707028c29a54fc5f60f873be5ca5a0a2ed..8f98c58e26891b3dd923e716435470f0bc2f36ae 100644 (file)
--- 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 4dcbc13e9ec8728285d333bdbf75e985a8604035..fa7050579e9afa125096eca89dc75c64a00cb788 100644 (file)
--- 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);