/*
* BIRD -- Bidirectional Forwarding Detection (BFD)
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
#include "bfd.h"
#include "lib/mac.h"
struct bfd_ctl_packet
{
u8 vdiag; /* Version and diagnostic */
u8 flags; /* State and flags */
u8 detect_mult;
u8 length; /* Whole packet length */
u32 snd_id; /* Sender ID, aka 'my discriminator' */
u32 rcv_id; /* Receiver ID, aka 'your discriminator' */
u32 des_min_tx_int;
u32 req_min_rx_int;
u32 req_min_echo_rx_int;
};
struct bfd_auth
{
u8 type; /* Authentication type (BFD_AUTH_*) */
u8 length; /* Authentication section length */
};
struct bfd_simple_auth
{
u8 type; /* BFD_AUTH_SIMPLE */
u8 length; /* Length of bfd_simple_auth + pasword length */
u8 key_id; /* Key ID */
byte password[0]; /* Password itself, variable length */
};
#define BFD_MAX_PASSWORD_LENGTH 16
struct bfd_crypto_auth
{
u8 type; /* BFD_AUTH_*_MD5 or BFD_AUTH_*_SHA1 */
u8 length; /* Length of bfd_crypto_auth + hash length */
u8 key_id; /* Key ID */
u8 zero; /* Reserved, zero on transmit */
u32 csn; /* Cryptographic sequence number */
byte data[0]; /* Authentication key/hash, length 16 or 20 */
};
#define BFD_BASE_LEN sizeof(struct bfd_ctl_packet)
#define BFD_MAX_LEN 64
#define DROP(DSC,VAL) do { err_dsc = DSC; err_val = VAL; goto drop; } while(0)
#define LOG_PKT(msg, args...) \
log(L_REMOTE "%s: " msg, p->p.name, args)
#define LOG_PKT_AUTH(msg, args...) \
log(L_AUTH "%s: " msg, p->p.name, args)
static inline u8 bfd_pack_vdiag(u8 version, u8 diag)
{ return (version << 5) | diag; }
static inline u8 bfd_pack_flags(u8 state, u8 flags)
{ return (state << 6) | flags; }
static inline u8 bfd_pkt_get_version(struct bfd_ctl_packet *pkt)
{ return pkt->vdiag >> 5; }
static inline u8 bfd_pkt_get_diag(struct bfd_ctl_packet *pkt)
{ return pkt->vdiag & 0x1f; }
static inline u8 bfd_pkt_get_state(struct bfd_ctl_packet *pkt)
{ return pkt->flags >> 6; }
static inline void UNUSED bfd_pkt_set_state(struct bfd_ctl_packet *pkt, u8 val)
{ pkt->flags = val << 6; }
char *
bfd_format_flags(u8 flags, char *buf)
{
char *bp = buf;
if (flags & BFD_FLAGS) *bp++ = ' ';
if (flags & BFD_FLAG_POLL) *bp++ = 'P';
if (flags & BFD_FLAG_FINAL) *bp++ = 'F';
if (flags & BFD_FLAG_CPI) *bp++ = 'C';
if (flags & BFD_FLAG_AP) *bp++ = 'A';
if (flags & BFD_FLAG_DEMAND) *bp++ = 'D';
if (flags & BFD_FLAG_MULTIPOINT) *bp++ = 'M';
*bp = 0;
return buf;
}
const u8 bfd_auth_type_to_hash_alg[] = {
[BFD_AUTH_NONE] = ALG_UNDEFINED,
[BFD_AUTH_SIMPLE] = ALG_UNDEFINED,
[BFD_AUTH_KEYED_MD5] = ALG_MD5,
[BFD_AUTH_METICULOUS_KEYED_MD5] = ALG_MD5,
[BFD_AUTH_KEYED_SHA1] = ALG_SHA1,
[BFD_AUTH_METICULOUS_KEYED_SHA1] = ALG_SHA1,
};
/* Fill authentication section and modifies final length in control section packet */
static void
bfd_fill_authentication(struct bfd_proto *p, struct bfd_session *s, struct bfd_ctl_packet *pkt)
{
struct bfd_iface_config *cf = s->ifa->cf;
struct password_item *pass = password_find(cf->passwords, 0);
uint meticulous = 0;
if (!pass)
{
/* FIXME: This should not happen */
log(L_ERR "%s: No suitable password found for authentication", p->p.name);
return;
}
switch (cf->auth_type)
{
case BFD_AUTH_SIMPLE:
{
struct bfd_simple_auth *auth = (void *) (pkt + 1);
uint pass_len = MIN(pass->length, BFD_MAX_PASSWORD_LENGTH);
auth->type = BFD_AUTH_SIMPLE;
auth->length = sizeof(struct bfd_simple_auth) + pass_len;
auth->key_id = pass->id;
pkt->flags |= BFD_FLAG_AP;
pkt->length += auth->length;
memcpy(auth->password, pass->password, pass_len);
return;
}
case BFD_AUTH_METICULOUS_KEYED_MD5:
case BFD_AUTH_METICULOUS_KEYED_SHA1:
meticulous = 1;
/* fallthrough */
case BFD_AUTH_KEYED_MD5:
case BFD_AUTH_KEYED_SHA1:
{
struct bfd_crypto_auth *auth = (void *) (pkt + 1);
uint hash_alg = bfd_auth_type_to_hash_alg[cf->auth_type];
uint hash_len = mac_type_length(pass->alg);
/* Increase CSN about one time per second */
u32 new_time = (u64) current_time() >> 20;
if ((new_time != s->tx_csn_time) || meticulous)
{
s->tx_csn++;
s->tx_csn_time = new_time;
}
DBG("[%I] CSN: %u\n", s->addr, s->last_tx_csn);
auth->type = cf->auth_type;
auth->length = sizeof(struct bfd_crypto_auth) + hash_len;
auth->key_id = pass->id;
auth->zero = 0;
auth->csn = htonl(s->tx_csn);
pkt->flags |= BFD_FLAG_AP;
pkt->length += auth->length;
strncpy(auth->data, pass->password, hash_len);
mac_fill(hash_alg, NULL, 0, (byte *) pkt, pkt->length, auth->data);
return;
}
}
}
static int
bfd_check_authentication(struct bfd_proto *p, struct bfd_session *s, struct bfd_ctl_packet *pkt)
{
struct bfd_iface_config *cf = s->ifa->cf;
const char *err_dsc = NULL;
uint err_val = 0;
uint auth_type = 0;
uint meticulous = 0;
if (pkt->flags & BFD_FLAG_AP)
{
struct bfd_auth *auth = (void *) (pkt + 1);
if ((pkt->length < (BFD_BASE_LEN + sizeof(struct bfd_auth))) ||
(pkt->length < (BFD_BASE_LEN + auth->length)))
DROP("packet length mismatch", pkt->length);
/* Zero is reserved, we use it as BFD_AUTH_NONE internally */
if (auth->type == 0)
DROP("reserved authentication type", 0);
auth_type = auth->type;
}
if (auth_type != cf->auth_type)
DROP("authentication method mismatch", auth_type);
switch (auth_type)
{
case BFD_AUTH_NONE:
return 1;
case BFD_AUTH_SIMPLE:
{
struct bfd_simple_auth *auth = (void *) (pkt + 1);
if (auth->length < sizeof(struct bfd_simple_auth))
DROP("wrong authentication length", auth->length);
struct password_item *pass = password_find_by_id(cf->passwords, auth->key_id);
if (!pass)
DROP("no suitable password found", auth->key_id);
uint pass_len = MIN(pass->length, BFD_MAX_PASSWORD_LENGTH);
uint auth_len = sizeof(struct bfd_simple_auth) + pass_len;
if ((auth->length != auth_len) || memcmp(auth->password, pass->password, pass_len))
DROP("wrong password", pass->id);
return 1;
}
case BFD_AUTH_METICULOUS_KEYED_MD5:
case BFD_AUTH_METICULOUS_KEYED_SHA1:
meticulous = 1;
/* fallthrough */
case BFD_AUTH_KEYED_MD5:
case BFD_AUTH_KEYED_SHA1:
{
struct bfd_crypto_auth *auth = (void *) (pkt + 1);
uint hash_alg = bfd_auth_type_to_hash_alg[cf->auth_type];
uint hash_len = mac_type_length(hash_alg);
if (auth->length != (sizeof(struct bfd_crypto_auth) + hash_len))
DROP("wrong authentication length", auth->length);
struct password_item *pass = password_find_by_id(cf->passwords, auth->key_id);
if (!pass)
DROP("no suitable password found", auth->key_id);
/* BFD CSNs are in 32-bit circular number space */
u32 csn = ntohl(auth->csn);
if (s->rx_csn_known &&
(((csn - s->rx_csn) > (3 * s->detect_mult)) ||
(meticulous && (csn == s->rx_csn))))
{
/* We want to report both new and old CSN */
LOG_PKT_AUTH("Authentication failed for %I - "
"wrong sequence number (rcv %u, old %u)",
s->addr, csn, s->rx_csn);
return 0;
}
byte *auth_data = alloca(hash_len);
memcpy(auth_data, auth->data, hash_len);
strncpy(auth->data, pass->password, hash_len);
if (!mac_verify(hash_alg, NULL, 0, (byte *) pkt, pkt->length, auth_data))
DROP("wrong authentication code", pass->id);
s->rx_csn = csn;
s->rx_csn_known = 1;
return 1;
}
}
drop:
LOG_PKT_AUTH("Authentication failed for %I - %s (%u)",
s->addr, err_dsc, err_val);
return 0;
}
void
bfd_send_ctl(struct bfd_proto *p, struct bfd_session *s, int final)
{
sock *sk = s->ifa->sk;
struct bfd_ctl_packet *pkt;
char fb[8];
if (!sk)
return;
pkt = (struct bfd_ctl_packet *) sk->tbuf;
pkt->vdiag = bfd_pack_vdiag(1, s->loc_diag);
pkt->flags = bfd_pack_flags(s->loc_state, 0);
pkt->detect_mult = s->detect_mult;
pkt->length = BFD_BASE_LEN;
pkt->snd_id = htonl(s->loc_id);
pkt->rcv_id = htonl(s->rem_id);
pkt->des_min_tx_int = htonl(s->des_min_tx_new);
pkt->req_min_rx_int = htonl(s->req_min_rx_new);
pkt->req_min_echo_rx_int = 0;
if (final)
pkt->flags |= BFD_FLAG_FINAL;
else if (s->poll_active)
pkt->flags |= BFD_FLAG_POLL;
if (s->ifa->cf->auth_type)
bfd_fill_authentication(p, s, pkt);
if (sk->tbuf != sk->tpos)
log(L_WARN "%s: Old packet overwritten in TX buffer", p->p.name);
TRACE(D_PACKETS, "Sending CTL to %I [%s%s]", s->addr,
bfd_state_names[s->loc_state], bfd_format_flags(pkt->flags, fb));
sk_send_to(sk, pkt->length, s->addr, sk->dport);
}
static int
bfd_rx_hook(sock *sk, uint len)
{
struct bfd_proto *p = sk->data;
struct bfd_ctl_packet *pkt = (struct bfd_ctl_packet *) sk->rbuf;
const char *err_dsc = NULL;
uint err_val = 0;
char fb[8];
if ((sk->sport == BFD_CONTROL_PORT) && (sk->rcv_ttl < 255))
DROP("wrong TTL", sk->rcv_ttl);
if (len < BFD_BASE_LEN)
DROP("too short", len);
u8 version = bfd_pkt_get_version(pkt);
if (version != 1)
DROP("version mismatch", version);
if ((pkt->length < BFD_BASE_LEN) || (pkt->length > len))
DROP("length mismatch", pkt->length);
if (pkt->detect_mult == 0)
DROP("invalid detect mult", 0);
if ((pkt->flags & BFD_FLAG_MULTIPOINT) ||
((pkt->flags & BFD_FLAG_POLL) && (pkt->flags & BFD_FLAG_FINAL)))
DROP("invalid flags", pkt->flags);
if (pkt->snd_id == 0)
DROP("invalid my discriminator", 0);
struct bfd_session *s;
u32 id = ntohl(pkt->rcv_id);
if (id)
{
s = bfd_find_session_by_id(p, id);
if (!s)
DROP("unknown session id", id);
}
else
{
u8 ps = bfd_pkt_get_state(pkt);
if (ps > BFD_STATE_DOWN)
DROP("invalid init state", ps);
s = bfd_find_session_by_addr(p, sk->faddr);
/* FIXME: better session matching and message */
if (!s)
return 1;
}
/* bfd_check_authentication() has its own error logging */
if (!bfd_check_authentication(p, s, pkt))
return 1;
u32 old_tx_int = s->des_min_tx_int;
u32 old_rx_int = s->rem_min_rx_int;
s->rem_id= ntohl(pkt->snd_id);
s->rem_state = bfd_pkt_get_state(pkt);
s->rem_diag = bfd_pkt_get_diag(pkt);
s->rem_demand_mode = pkt->flags & BFD_FLAG_DEMAND;
s->rem_min_tx_int = ntohl(pkt->des_min_tx_int);
s->rem_min_rx_int = ntohl(pkt->req_min_rx_int);
s->rem_detect_mult = pkt->detect_mult;
TRACE(D_PACKETS, "CTL received from %I [%s%s]", sk->faddr,
bfd_state_names[s->rem_state], bfd_format_flags(pkt->flags, fb));
bfd_session_process_ctl(s, pkt->flags, old_tx_int, old_rx_int);
return 1;
drop:
LOG_PKT("Bad packet from %I - %s (%u)", sk->faddr, err_dsc, err_val);
return 1;
}
static void
bfd_err_hook(sock *sk, int err)
{
struct bfd_proto *p = sk->data;
log(L_ERR "%s: Socket error: %m", p->p.name, err);
}
sock *
bfd_open_rx_sk(struct bfd_proto *p, int multihop)
{
sock *sk = sk_new(p->tpool);
sk->type = SK_UDP;
sk->sport = !multihop ? BFD_CONTROL_PORT : BFD_MULTI_CTL_PORT;
sk->vrf = p->p.vrf;
sk->data = p;
sk->rbsize = BFD_MAX_LEN;
sk->rx_hook = bfd_rx_hook;
sk->err_hook = bfd_err_hook;
/* TODO: configurable ToS and priority */
sk->tos = IP_PREC_INTERNET_CONTROL;
sk->priority = sk_priority_control;
sk->flags = SKF_THREAD | SKF_LADDR_RX | (!multihop ? SKF_TTL_RX : 0);
#ifdef IPV6
sk->flags |= SKF_V6ONLY;
#endif
if (sk_open(sk) < 0)
goto err;
sk_start(sk);
return sk;
err:
sk_log_error(sk, p->p.name);
rfree(sk);
return NULL;
}
sock *
bfd_open_tx_sk(struct bfd_proto *p, ip_addr local, struct iface *ifa)
{
sock *sk = sk_new(p->tpool);
sk->type = SK_UDP;
sk->saddr = local;
sk->dport = ifa ? BFD_CONTROL_PORT : BFD_MULTI_CTL_PORT;
sk->iface = ifa;
sk->vrf = p->p.vrf;
sk->data = p;
sk->tbsize = BFD_MAX_LEN;
sk->err_hook = bfd_err_hook;
/* TODO: configurable ToS, priority and TTL security */
sk->tos = IP_PREC_INTERNET_CONTROL;
sk->priority = sk_priority_control;
sk->ttl = ifa ? 255 : -1;
sk->flags = SKF_THREAD | SKF_BIND | SKF_HIGH_PORT;
#ifdef IPV6
sk->flags |= SKF_V6ONLY;
#endif
if (sk_open(sk) < 0)
goto err;
sk_start(sk);
return sk;
err:
sk_log_error(sk, p->p.name);
rfree(sk);
return NULL;
}
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