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net/tcp: Ignore specific ICMPs for TCP-AO connections

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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>
This commit is contained in:
Dmitry Safonov 2023-10-23 20:22:08 +01:00 committed by David S. Miller
parent 2717b5adea
commit 953af8e3ac
7 changed files with 87 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
include/net/tcp_ao.h
View File

@ -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)

1
include/uapi/linux/snmp.h
View File

@ -301,6 +301,7 @@ enum
LINUX_MIB_TCPAOBAD, /* TCPAOBad */
LINUX_MIB_TCPAOKEYNOTFOUND, /* TCPAOKeyNotFound */
LINUX_MIB_TCPAOGOOD, /* TCPAOGood */
LINUX_MIB_TCPAODROPPEDICMPS, /* TCPAODroppedIcmps */
__LINUX_MIB_MAX
};

4
include/uapi/linux/tcp.h
View File

@ -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, ...) */

1
net/ipv4/proc.c
View File

@ -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
};

58
net/ipv4/tcp_ao.c
View File

@ -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)

7
net/ipv4/tcp_ipv4.c
View File

@ -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.

7
net/ipv6/tcp_ipv6.c
View File

@ -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);