diff --git a/ssh.c b/ssh.c index 0cc27c93..5ed63cc2 100644 --- a/ssh.c +++ b/ssh.c @@ -768,6 +768,7 @@ struct ssh_tag { const struct ssh2_cipher *cscipher, *sccipher; void *cs_cipher_ctx, *sc_cipher_ctx; const struct ssh_mac *csmac, *scmac; + int csmac_etm, scmac_etm; void *cs_mac_ctx, *sc_mac_ctx; const struct ssh_compress *cscomp, *sccomp; void *cs_comp_ctx, *sc_comp_ctx; @@ -1566,7 +1567,7 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen) st->maclen = ssh->scmac ? ssh->scmac->len : 0; if (ssh->sccipher && (ssh->sccipher->flags & SSH_CIPHER_IS_CBC) && - ssh->scmac) { + ssh->scmac && !ssh->scmac_etm) { /* * When dealing with a CBC-mode cipher, we want to avoid the * possibility of an attacker's tweaking the ciphertext stream @@ -1578,6 +1579,11 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen) * length, so we just read data and check the MAC repeatedly, * and when the MAC passes, see if the length we've got is * plausible. + * + * This defence is unnecessary in OpenSSH ETM mode, because + * the whole point of ETM mode is that the attacker can't + * tweak the ciphertext stream at all without the MAC + * detecting it before we decrypt anything. */ /* May as well allocate the whole lot now. */ @@ -1632,6 +1638,71 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen) st->pktin->data = sresize(st->pktin->data, st->pktin->maxlen + APIEXTRA, unsigned char); + } else if (ssh->scmac && ssh->scmac_etm) { + st->pktin->data = snewn(4 + APIEXTRA, unsigned char); + + /* + * OpenSSH encrypt-then-MAC mode: the packet length is + * unencrypted. + */ + for (st->i = st->len = 0; st->i < 4; st->i++) { + while ((*datalen) == 0) + crReturn(NULL); + st->pktin->data[st->i] = *(*data)++; + (*datalen)--; + } + st->len = toint(GET_32BIT(st->pktin->data)); + + /* + * _Completely_ silly lengths should be stomped on before they + * do us any more damage. + */ + if (st->len < 0 || st->len > OUR_V2_PACKETLIMIT || + st->len % st->cipherblk != 0) { + bombout(("Incoming packet length field was garbled")); + ssh_free_packet(st->pktin); + crStop(NULL); + } + + /* + * So now we can work out the total packet length. + */ + st->packetlen = st->len + 4; + + /* + * Allocate memory for the rest of the packet. + */ + st->pktin->maxlen = st->packetlen + st->maclen; + st->pktin->data = sresize(st->pktin->data, + st->pktin->maxlen + APIEXTRA, + unsigned char); + + /* + * Read the remainder of the packet. + */ + for (st->i = 4; st->i < st->packetlen + st->maclen; st->i++) { + while ((*datalen) == 0) + crReturn(NULL); + st->pktin->data[st->i] = *(*data)++; + (*datalen)--; + } + + /* + * Check the MAC. + */ + if (ssh->scmac + && !ssh->scmac->verify(ssh->sc_mac_ctx, st->pktin->data, + st->len + 4, st->incoming_sequence)) { + bombout(("Incorrect MAC received on packet")); + ssh_free_packet(st->pktin); + crStop(NULL); + } + + /* Decrypt everything between the length field and the MAC. */ + if (ssh->sccipher) + ssh->sccipher->decrypt(ssh->sc_cipher_ctx, + st->pktin->data + 4, + st->packetlen - 4); } else { st->pktin->data = snewn(st->cipherblk + APIEXTRA, unsigned char); @@ -2146,7 +2217,7 @@ static struct Packet *ssh2_pkt_init(int pkt_type) */ static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt) { - int cipherblk, maclen, padding, i; + int cipherblk, maclen, padding, unencrypted_prefix, i; if (ssh->logctx) ssh2_log_outgoing_packet(ssh, pkt); @@ -2187,10 +2258,12 @@ static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt) cipherblk = ssh->cscipher ? ssh->cscipher->blksize : 8; /* block size */ cipherblk = cipherblk < 8 ? 8 : cipherblk; /* or 8 if blksize < 8 */ padding = 4; + unencrypted_prefix = (ssh->csmac && ssh->csmac_etm) ? 4 : 0; if (pkt->length + padding < pkt->forcepad) padding = pkt->forcepad - pkt->length; padding += - (cipherblk - (pkt->length + padding) % cipherblk) % cipherblk; + (cipherblk - (pkt->length - unencrypted_prefix + padding) % cipherblk) + % cipherblk; assert(padding <= 255); maclen = ssh->csmac ? ssh->csmac->len : 0; ssh2_pkt_ensure(pkt, pkt->length + padding + maclen); @@ -2198,16 +2271,30 @@ static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt) for (i = 0; i < padding; i++) pkt->data[pkt->length + i] = random_byte(); PUT_32BIT(pkt->data, pkt->length + padding - 4); - if (ssh->csmac) - ssh->csmac->generate(ssh->cs_mac_ctx, pkt->data, - pkt->length + padding, - ssh->v2_outgoing_sequence); + if (ssh->csmac && ssh->csmac_etm) { + /* + * OpenSSH-defined encrypt-then-MAC protocol. + */ + if (ssh->cscipher) + ssh->cscipher->encrypt(ssh->cs_cipher_ctx, + pkt->data + 4, pkt->length + padding - 4); + ssh->csmac->generate(ssh->cs_mac_ctx, pkt->data, + pkt->length + padding, + ssh->v2_outgoing_sequence); + } else { + /* + * SSH-2 standard protocol. + */ + if (ssh->csmac) + ssh->csmac->generate(ssh->cs_mac_ctx, pkt->data, + pkt->length + padding, + ssh->v2_outgoing_sequence); + if (ssh->cscipher) + ssh->cscipher->encrypt(ssh->cs_cipher_ctx, + pkt->data, pkt->length + padding); + } + ssh->v2_outgoing_sequence++; /* whether or not we MACed */ - - if (ssh->cscipher) - ssh->cscipher->encrypt(ssh->cs_cipher_ctx, - pkt->data, pkt->length + padding); - pkt->encrypted_len = pkt->length + padding; /* Ready-to-send packet starts at pkt->data. We return length. */ @@ -6072,6 +6159,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, const struct ssh2_cipher *sccipher_tobe; const struct ssh_mac *csmac_tobe; const struct ssh_mac *scmac_tobe; + int csmac_etm_tobe, scmac_etm_tobe; const struct ssh_compress *cscomp_tobe; const struct ssh_compress *sccomp_tobe; char *hostkeydata, *sigdata, *rsakeydata, *keystr, *fingerprint; @@ -6255,8 +6343,15 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, /* List MAC algorithms (client->server then server->client). */ for (j = 0; j < 2; j++) { ssh2_pkt_addstring_start(s->pktout); - for (i = 0; i < s->nmacs; i++) + for (i = 0; i < s->nmacs; i++) { ssh2_pkt_addstring_commasep(s->pktout, s->maclist[i]->name); + } + for (i = 0; i < s->nmacs; i++) { + /* For each MAC, there may also be an ETM version, + * which we list second. */ + if (s->maclist[i]->etm_name) + ssh2_pkt_addstring_commasep(s->pktout, s->maclist[i]->etm_name); + } } /* List client->server compression algorithms, * then server->client compression algorithms. (We use the @@ -6434,9 +6529,25 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, for (i = 0; i < s->nmacs; i++) { if (in_commasep_string(s->maclist[i]->name, str, len)) { s->csmac_tobe = s->maclist[i]; - break; + s->csmac_etm_tobe = FALSE; + break; } } + if (!s->csmac_tobe) { + for (i = 0; i < s->nmacs; i++) { + if (s->maclist[i]->etm_name && + in_commasep_string(s->maclist[i]->etm_name, str, len)) { + s->csmac_tobe = s->maclist[i]; + s->csmac_etm_tobe = TRUE; + break; + } + } + } + if (!s->csmac_tobe) { + bombout(("Couldn't agree a client-to-server MAC" + " (available: %.*s)", len, str)); + crStopV; + } ssh_pkt_getstring(pktin, &str, &len); /* server->client mac */ if (!str) { bombout(("KEXINIT packet was incomplete")); @@ -6445,9 +6556,25 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, for (i = 0; i < s->nmacs; i++) { if (in_commasep_string(s->maclist[i]->name, str, len)) { s->scmac_tobe = s->maclist[i]; - break; + s->scmac_etm_tobe = FALSE; + break; } } + if (!s->scmac_tobe) { + for (i = 0; i < s->nmacs; i++) { + if (s->maclist[i]->etm_name && + in_commasep_string(s->maclist[i]->etm_name, str, len)) { + s->scmac_tobe = s->maclist[i]; + s->scmac_etm_tobe = TRUE; + break; + } + } + } + if (!s->scmac_tobe) { + bombout(("Couldn't agree a server-to-client MAC" + " (available: %.*s)", len, str)); + crStopV; + } ssh_pkt_getstring(pktin, &str, &len); /* client->server compression */ if (!str) { bombout(("KEXINIT packet was incomplete")); @@ -7003,6 +7130,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, if (ssh->cs_mac_ctx) ssh->csmac->free_context(ssh->cs_mac_ctx); ssh->csmac = s->csmac_tobe; + ssh->csmac_etm = s->csmac_etm_tobe; ssh->cs_mac_ctx = ssh->csmac->make_context(); if (ssh->cs_comp_ctx) @@ -7034,8 +7162,9 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, logeventf(ssh, "Initialised %.200s client->server encryption", ssh->cscipher->text_name); - logeventf(ssh, "Initialised %.200s client->server MAC algorithm", - ssh->csmac->text_name); + logeventf(ssh, "Initialised %.200s client->server MAC algorithm%s", + ssh->csmac->text_name, + ssh->csmac_etm ? " (in ETM mode)" : ""); if (ssh->cscomp->text_name) logeventf(ssh, "Initialised %s compression", ssh->cscomp->text_name); @@ -7069,6 +7198,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, if (ssh->sc_mac_ctx) ssh->scmac->free_context(ssh->sc_mac_ctx); ssh->scmac = s->scmac_tobe; + ssh->scmac_etm = s->scmac_etm_tobe; ssh->sc_mac_ctx = ssh->scmac->make_context(); if (ssh->sc_comp_ctx) @@ -7099,8 +7229,9 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen, } logeventf(ssh, "Initialised %.200s server->client encryption", ssh->sccipher->text_name); - logeventf(ssh, "Initialised %.200s server->client MAC algorithm", - ssh->scmac->text_name); + logeventf(ssh, "Initialised %.200s server->client MAC algorithm%s", + ssh->scmac->text_name, + ssh->scmac_etm ? " (in ETM mode)" : ""); if (ssh->sccomp->text_name) logeventf(ssh, "Initialised %s decompression", ssh->sccomp->text_name); diff --git a/ssh.h b/ssh.h index 29f12d89..7f452399 100644 --- a/ssh.h +++ b/ssh.h @@ -296,7 +296,7 @@ struct ssh_mac { void (*bytes) (void *, unsigned char const *, int); void (*genresult) (void *, unsigned char *); int (*verresult) (void *, unsigned char const *); - char *name; + char *name, *etm_name; int len; char *text_name; }; diff --git a/sshmd5.c b/sshmd5.c index 2fdb5900..af139690 100644 --- a/sshmd5.c +++ b/sshmd5.c @@ -334,7 +334,7 @@ const struct ssh_mac ssh_hmac_md5 = { hmacmd5_make_context, hmacmd5_free_context, hmacmd5_key_16, hmacmd5_generate, hmacmd5_verify, hmacmd5_start, hmacmd5_bytes, hmacmd5_genresult, hmacmd5_verresult, - "hmac-md5", + "hmac-md5", "hmac-md5-etm@openssh.com", 16, "HMAC-MD5" }; diff --git a/sshsh256.c b/sshsh256.c index 60c5217f..7ea25fbe 100644 --- a/sshsh256.c +++ b/sshsh256.c @@ -323,7 +323,7 @@ const struct ssh_mac ssh_hmac_sha256 = { sha256_generate, sha256_verify, hmacsha256_start, hmacsha256_bytes, hmacsha256_genresult, hmacsha256_verresult, - "hmac-sha2-256", + "hmac-sha2-256", "hmac-sha2-256-etm@openssh.com", 32, "HMAC-SHA-256" }; diff --git a/sshsha.c b/sshsha.c index a5b3a60c..f22035fe 100644 --- a/sshsha.c +++ b/sshsha.c @@ -400,7 +400,7 @@ const struct ssh_mac ssh_hmac_sha1 = { sha1_make_context, sha1_free_context, sha1_key, sha1_generate, sha1_verify, hmacsha1_start, hmacsha1_bytes, hmacsha1_genresult, hmacsha1_verresult, - "hmac-sha1", + "hmac-sha1", "hmac-sha1-etm@openssh.com", 20, "HMAC-SHA1" }; @@ -410,7 +410,7 @@ const struct ssh_mac ssh_hmac_sha1_96 = { sha1_96_generate, sha1_96_verify, hmacsha1_start, hmacsha1_bytes, hmacsha1_96_genresult, hmacsha1_96_verresult, - "hmac-sha1-96", + "hmac-sha1-96", "hmac-sha1-96-etm@openssh.com", 12, "HMAC-SHA1-96" }; @@ -419,7 +419,7 @@ const struct ssh_mac ssh_hmac_sha1_buggy = { sha1_make_context, sha1_free_context, sha1_key_buggy, sha1_generate, sha1_verify, hmacsha1_start, hmacsha1_bytes, hmacsha1_genresult, hmacsha1_verresult, - "hmac-sha1", + "hmac-sha1", NULL, 20, "bug-compatible HMAC-SHA1" }; @@ -429,7 +429,7 @@ const struct ssh_mac ssh_hmac_sha1_96_buggy = { sha1_96_generate, sha1_96_verify, hmacsha1_start, hmacsha1_bytes, hmacsha1_96_genresult, hmacsha1_96_verresult, - "hmac-sha1-96", + "hmac-sha1-96", NULL, 12, "bug-compatible HMAC-SHA1-96" };