[PATCH v6 16/21] net/tcp: Ignore specific ICMPs for TCP-AO connections
From: Dmitry Safonov
Date: Fri May 12 2023 - 16:24:47 EST
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 | 10 ++++++-
include/uapi/linux/snmp.h | 1 +
include/uapi/linux/tcp.h | 4 ++-
net/ipv4/proc.c | 1 +
net/ipv4/tcp_ao.c | 62 +++++++++++++++++++++++++++++++++++++++
net/ipv4/tcp_ipv4.c | 5 ++++
net/ipv6/tcp_ipv6.c | 4 +++
7 files changed, 85 insertions(+), 2 deletions(-)
diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index 391b8260c325..a99521b78147 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 {
@@ -94,7 +95,8 @@ 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;
u32 snd_sne;
@@ -174,6 +176,7 @@ int tcp_ao_calc_traffic_key(struct tcp_ao_key *mkt, u8 *key, void *ctx,
void tcp_ao_destroy_sock(struct sock *sk, bool twsk);
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);
+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,
@@ -248,6 +251,11 @@ static inline void tcp_ao_syncookie(struct sock *sk, const struct sk_buff *skb,
{
}
+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 06ddf4cd295c..47a6b47da66f 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -300,6 +300,7 @@ 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 3fe0612ec59a..ca7ed18ce67b 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -392,7 +392,8 @@ 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 */
@@ -400,6 +401,7 @@ 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 3f643cd29cfe..5d3c9c96773e 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -302,6 +302,7 @@ 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 2f030cd5e605..fdba3e1c80cc 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 +53,64 @@ 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->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;
+}
+EXPORT_SYMBOL_GPL(tcp_ao_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/port/VRF/etc.
@@ -938,6 +997,7 @@ 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;
@@ -1618,9 +1678,11 @@ 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 9db6d7118c28..791453dabf88 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -492,6 +492,8 @@ 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;
}
@@ -506,6 +508,9 @@ 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 6918076e1552..3ed15011876b 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);
--
2.40.0