/*
* Fetch list of identities held by the agent.
*/
int
ssh_fetch_identitylist(int sock, int version, struct ssh_identitylist **idlp)
{
u_char type, code1 = 0, code2 = 0;
u_int32_t num, i;
struct sshbuf *msg;
struct ssh_identitylist *idl = NULL;
int r;
/* Determine request and expected response types */
switch (version) {
case 1:
code1 = SSH_AGENTC_REQUEST_RSA_IDENTITIES;
code2 = SSH_AGENT_RSA_IDENTITIES_ANSWER;
break;
case 2:
code1 = SSH2_AGENTC_REQUEST_IDENTITIES;
code2 = SSH2_AGENT_IDENTITIES_ANSWER;
break;
default:
return SSH_ERR_INVALID_ARGUMENT;
}
/*
* Send a message to the agent requesting for a list of the
* identities it can represent.
*/
if ((msg = sshbuf_new()) == NULL)
return SSH_ERR_ALLOC_FAIL;
if ((r = sshbuf_put_u8(msg, code1)) != 0)
goto out;
if ((r = ssh_request_reply(sock, msg, msg)) != 0)
goto out;
/* Get message type, and verify that we got a proper answer. */
if ((r = sshbuf_get_u8(msg, &type)) != 0)
goto out;
if (agent_failed(type)) {
r = SSH_ERR_AGENT_FAILURE;
goto out;
} else if (type != code2) {
r = SSH_ERR_INVALID_FORMAT;
goto out;
}
/* Get the number of entries in the response and check it for sanity. */
if ((r = sshbuf_get_u32(msg, &num)) != 0)
goto out;
if (num > MAX_AGENT_IDENTITIES) {
r = SSH_ERR_INVALID_FORMAT;
goto out;
}
if (num == 0) {
r = SSH_ERR_AGENT_NO_IDENTITIES;
goto out;
}
/* Deserialise the response into a list of keys/comments */
if ((idl = calloc(1, sizeof(*idl))) == NULL ||
(idl->keys = calloc(num, sizeof(*idl->keys))) == NULL ||
(idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
for (i = 0; i < num;) {
switch (version) {
case 1:
#ifdef WITH_SSH1
if ((r = deserialise_identity1(msg,
&(idl->keys[i]), &(idl->comments[i]))) != 0)
goto out;
#endif
break;
case 2:
if ((r = deserialise_identity2(msg,
&(idl->keys[i]), &(idl->comments[i]))) != 0) {
if (r == SSH_ERR_KEY_TYPE_UNKNOWN) {
/* Gracefully skip unknown key types */
num--;
continue;
} else
goto out;
}
break;
}
i++;
}
idl->nkeys = num;
*idlp = idl;
idl = NULL;
r = 0;
out:
sshbuf_free(msg);
if (idl != NULL)
ssh_free_identitylist(idl);
return r;
}
/*
* Checks if the user has an authentication agent, and if so, tries to
* authenticate using the agent.
*/
static int
try_agent_authentication(struct ssh *ssh)
{
int r, type, agent_fd, ret = 0;
u_char response[16];
size_t i;
BIGNUM *challenge;
struct ssh_identitylist *idlist = NULL;
/* Get connection to the agent. */
if ((r = ssh_get_authentication_socket(&agent_fd)) != 0) {
if (r != SSH_ERR_AGENT_NOT_PRESENT)
debug("%s: ssh_get_authentication_socket: %s",
__func__, ssh_err(r));
return 0;
}
if ((challenge = BN_new()) == NULL)
fatal("try_agent_authentication: BN_new failed");
/* Loop through identities served by the agent. */
if ((r = ssh_fetch_identitylist(agent_fd, 1, &idlist)) != 0) {
if (r != SSH_ERR_AGENT_NO_IDENTITIES)
debug("%s: ssh_fetch_identitylist: %s",
__func__, ssh_err(r));
goto out;
}
for (i = 0; i < idlist->nkeys; i++) {
/* Try this identity. */
debug("Trying RSA authentication via agent with '%.100s'",
idlist->comments[i]);
/*
* Tell the server that we are willing to authenticate
* using this key.
*/
if ((r = sshpkt_start(ssh, SSH_CMSG_AUTH_RSA)) != 0 ||
(r = sshpkt_put_bignum1(ssh, idlist->keys[i]->rsa->n)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
fatal("%s: %s", __func__, ssh_err(r));
ssh_packet_write_wait(ssh);
/* Wait for server's response. */
type = ssh_packet_read(ssh);
/* The server sends failure if it doesn't like our key or
does not support RSA authentication. */
if (type == SSH_SMSG_FAILURE) {
debug("Server refused our key.");
continue;
}
/* Otherwise it should have sent a challenge. */
if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
ssh_packet_disconnect(ssh, "Protocol error during RSA "
"authentication: %d", type);
if ((r = sshpkt_get_bignum1(ssh, challenge)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
fatal("%s: %s", __func__, ssh_err(r));
debug("Received RSA challenge from server.");
/* Ask the agent to decrypt the challenge. */
if ((r = ssh_decrypt_challenge(agent_fd, idlist->keys[i],
challenge, session_id, response)) != 0) {
/*
* The agent failed to authenticate this identifier
* although it advertised it supports this. Just
* return a wrong value.
*/
logit("Authentication agent failed to decrypt "
"challenge: %s", ssh_err(r));
memset(response, 0, sizeof(response));
}
debug("Sending response to RSA challenge.");
/* Send the decrypted challenge back to the server. */
if ((r = sshpkt_start(ssh, SSH_CMSG_AUTH_RSA_RESPONSE)) != 0 ||
(r = sshpkt_put(ssh, &response, sizeof(response))) != 0 ||
(r = sshpkt_send(ssh)) != 0)
fatal("%s: %s", __func__, ssh_err(r));
ssh_packet_write_wait(ssh);
/* Wait for response from the server. */
type = ssh_packet_read(ssh);
/*
* The server returns success if it accepted the
* authentication.
*/
if (type == SSH_SMSG_SUCCESS) {
debug("RSA authentication accepted by server.");
ret = 1;
break;
} else if (type != SSH_SMSG_FAILURE)
ssh_packet_disconnect(ssh, "Protocol error waiting RSA auth "
"response: %d", type);
}
if (ret != 1)
debug("RSA authentication using agent refused.");
out:
ssh_free_identitylist(idlist);
ssh_close_authentication_socket(agent_fd);
BN_clear_free(challenge);
return ret;
}
