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Don't wait for KEX_INIT prior to sending our own packet.

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Watch out for bad KEX_INIT guesses and burn packets if necessary.
This commit is contained in:
Sara Golemon 2006-06-22 18:45:29 +00:00
parent 5f85317efa
commit adee5e5653
4 changed files with 104 additions and 6 deletions
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4
README
View File

@ -10,6 +10,10 @@ Version 0.14
Swap ordering of packet_add/packet-inspection to avoid inspect after free. (Selcuk)
Swap KEX_INIT ordering, send our KEX_INIT first.
Add check for oportunistic KEX_INIT packets. Burn bad guess if necessary.
Fix OpenSSL detection using pkg-config. (Dan Casey)
Version 0.13

2
include/libssh2_priv.h
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@ -199,6 +199,7 @@ struct _LIBSSH2_SESSION {
/* Agreed Key Exchange Method */
LIBSSH2_KEX_METHOD *kex;
int burn_optimistic_kexinit:1;
unsigned char *session_id;
unsigned long session_id_len;
@ -462,6 +463,7 @@ int libssh2_packet_require_ex(LIBSSH2_SESSION *session, unsigned char packet_typ
int libssh2_packet_requirev_ex(LIBSSH2_SESSION *session, unsigned char *packet_types, unsigned char **data, unsigned long *data_len, unsigned long match_ofs, const unsigned char *match_buf, unsigned long match_len);
#define libssh2_packet_requirev(session, packet_types, data, data_len) \
libssh2_packet_requirev_ex((session), (packet_types), (data), (data_len), 0, NULL, 0)
int libssh2_packet_burn(LIBSSH2_SESSION *session);
int libssh2_packet_write(LIBSSH2_SESSION *session, unsigned char *data, unsigned long data_len);
int libssh2_kex_exchange(LIBSSH2_SESSION *session, int reexchange);
unsigned long libssh2_channel_nextid(LIBSSH2_SESSION *session);

62
src/kex.c
View File

@ -118,6 +118,26 @@ static int libssh2_kex_method_diffie_hellman_groupGP_sha1_key_exchange(LIBSSH2_S
goto clean_exit;
}
if (session->burn_optimistic_kexinit) {
/* The first KEX packet to come along will be the guess initially sent by the server
* That guess turned out to be wrong so we need to silently ignore it */
int burn_type;
#ifdef LIBSSH2_DEBUG_KEX
_libssh2_debug(session, LIBSSH2_DBG_KEX, "Waiting for badly guessed KEX packet (to be ignored)");
#endif
burn_type = libssh2_packet_burn(session);
if (burn_type <= 0) {
/* Failed to receive a packet */
ret = -1;
goto clean_exit;
}
session->burn_optimistic_kexinit = 0;
#ifdef LIBSSH2_DEBUG_KEX
_libssh2_debug(session, LIBSSH2_DBG_KEX, "Burnt packet of type: %02x", (unsigned int)burn_type);
#endif
}
/* Wait for KEX reply */
if (libssh2_packet_require(session, packet_type_reply, &s_packet, &s_packet_len)) {
libssh2_error(session, LIBSSH2_ERROR_TIMEOUT, "Timed out waiting for KEX reply", 0);
@ -967,9 +987,9 @@ static int libssh2_kex_agree_kex_hostkey(LIBSSH2_SESSION *session, unsigned char
s = session->kex_prefs;
while (s && *s) {
unsigned char *p = strchr(s, ',');
unsigned char *q, *p = strchr(s, ',');
int method_len = (p ? (p - s) : strlen(s));
if (libssh2_kex_agree_instr(kex, kex_len, s, method_len)) {
if ((q = libssh2_kex_agree_instr(kex, kex_len, s, method_len))) {
LIBSSH2_KEX_METHOD *method = (LIBSSH2_KEX_METHOD*)libssh2_get_method_by_name(s, method_len, (LIBSSH2_COMMON_METHOD**)kexp);
if (!method) {
@ -982,6 +1002,12 @@ static int libssh2_kex_agree_kex_hostkey(LIBSSH2_SESSION *session, unsigned char
*/
if (libssh2_kex_agree_hostkey(session, method->flags, hostkey, hostkey_len) == 0) {
session->kex = method;
if (session->burn_optimistic_kexinit && (kex == q)) {
/* Server sent an optimistic packet,
* and client agrees with preference
* cancel burning the first KEX_INIT packet that comes in */
session->burn_optimistic_kexinit = 0;
}
return 0;
}
}
@ -999,6 +1025,12 @@ static int libssh2_kex_agree_kex_hostkey(LIBSSH2_SESSION *session, unsigned char
*/
if (libssh2_kex_agree_hostkey(session, (*kexp)->flags, hostkey, hostkey_len) == 0) {
session->kex = *kexp;
if (session->burn_optimistic_kexinit && (kex == s)) {
/* Server sent an optimistic packet,
* and client agrees with preference
* cancel burning the first KEX_INIT packet that comes in */
session->burn_optimistic_kexinit = 0;
}
return 0;
}
}
@ -1174,6 +1206,12 @@ static int libssh2_kex_agree_methods(LIBSSH2_SESSION *session, unsigned char *da
lang_cs_len = libssh2_ntohu32(s); lang_cs = s + 4; s += 4 + lang_cs_len;
lang_sc_len = libssh2_ntohu32(s); lang_sc = s + 4; s += 4 + lang_sc_len;
/* If the server sent an optimistic packet, assume that it guessed wrong.
* If the guess is determined to be right (by libssh2_kex_agree_kex_hostkey)
* This flag will be reset to zero so that it's not ignored */
session->burn_optimistic_kexinit = *(s++);
/* Next uint32 in packet is all zeros (reserved) */
if (libssh2_kex_agree_kex_hostkey(session, kex, kex_len, hostkey, hostkey_len)) {
return -1;
}
@ -1248,7 +1286,23 @@ int libssh2_kex_exchange(LIBSSH2_SESSION *session, int reexchange) /* session->f
}
if (!session->kex || !session->hostkey) {
/* Preserve in case of failure */
unsigned char *oldlocal = session->local.kexinit;
unsigned long oldlocal_len = session->local.kexinit_len;
session->local.kexinit = NULL;
if (libssh2_kexinit(session)) {
session->local.kexinit = oldlocal;
session->local.kexinit_len = oldlocal_len;
return -1;
}
if (libssh2_packet_require(session, SSH_MSG_KEXINIT, &data, &data_len)) {
if (session->local.kexinit) {
LIBSSH2_FREE(session, session->local.kexinit);
}
session->local.kexinit = oldlocal;
session->local.kexinit_len = oldlocal_len;
return -1;
}
@ -1258,10 +1312,6 @@ int libssh2_kex_exchange(LIBSSH2_SESSION *session, int reexchange) /* session->f
session->remote.kexinit = data;
session->remote.kexinit_len = data_len;
if (libssh2_kexinit(session)) {
return -1;
}
if (libssh2_kex_agree_methods(session, data, data_len)) {
return -1;
}

42
src/packet.c
View File

@ -1017,6 +1017,48 @@ int libssh2_packet_require_ex(LIBSSH2_SESSION *session, unsigned char packet_typ
}
/* }}} */
/* {{{ libssh2_packet_burn
* Loops libssh2_packet_read() until any packet is available and promptly discards it
* Used during KEX exchange to discard badly guessed KEX_INIT packets
*/
int libssh2_packet_burn(LIBSSH2_SESSION *session)
{
unsigned char *data;
unsigned long data_len;
char all_packets[255];
int i;
for(i = 1; i < 256; i++) all_packets[i - 1] = i;
if (libssh2_packet_askv_ex(session, all_packets, &data, &data_len, 0, NULL, 0, 0) == 0) {
i = data[0];
/* A packet was available in the packet brigade, burn it */
LIBSSH2_FREE(session, data);
return i;
}
#ifdef LIBSSH2_DEBUG_TRANSPORT
_libssh2_debug(session, LIBSSH2_DBG_TRANS, "Blocking until packet becomes available to burn");
#endif
while (session->socket_state == LIBSSH2_SOCKET_CONNECTED) {
int ret = libssh2_packet_read(session, 1);
if (ret < 0) {
return -1;
}
if (ret == 0) continue;
/* Be lazy, let packet_ask pull it out of the brigade */
if (0 == libssh2_packet_ask_ex(session, ret, &data, &data_len, 0, NULL, 0, 0)) {
/* Smoke 'em if you got 'em */
LIBSSH2_FREE(session, data);
return ret;
}
}
/* Only reached if the socket died */
return -1;
}
/* }}} */
/* {{{ libssh2_packet_requirev
* Loops libssh2_packet_read() until one of a list of packet types requested is available
* SSH_DISCONNECT or a SOCKET_DISCONNECTED will cause a bailout