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cli-agentfwd.c
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cli-agentfwd.c
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/*
* Dropbear - a SSH2 server
*
* Copyright (c) 2005 Matt Johnston
* All rights reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE. */
#include "includes.h"
#if DROPBEAR_CLI_AGENTFWD
#include "agentfwd.h"
#include "session.h"
#include "ssh.h"
#include "dbutil.h"
#include "chansession.h"
#include "channel.h"
#include "packet.h"
#include "buffer.h"
#include "dbrandom.h"
#include "listener.h"
#include "runopts.h"
#include "atomicio.h"
#include "signkey.h"
#include "auth.h"
/* The protocol implemented to talk to OpenSSH's SSH2 agent is documented in
PROTOCOL.agent in recent OpenSSH source distributions (5.1p1 has it). */
static int new_agent_chan(struct Channel * channel);
const struct ChanType cli_chan_agent = {
0, /* sepfds */
"auth-agent@openssh.com",
new_agent_chan,
NULL,
NULL,
NULL
};
static int connect_agent() {
int fd = -1;
char* agent_sock = NULL;
agent_sock = getenv("SSH_AUTH_SOCK");
if (agent_sock == NULL)
return -1;
fd = connect_unix(agent_sock);
if (fd < 0) {
dropbear_log(LOG_INFO, "Failed to connect to agent");
}
return fd;
}
/* handle a request for a connection to the locally running ssh-agent
or forward. */
static int new_agent_chan(struct Channel * channel) {
int fd = -1;
if (!cli_opts.agent_fwd)
return SSH_OPEN_ADMINISTRATIVELY_PROHIBITED;
fd = connect_agent();
if (fd < 0) {
return SSH_OPEN_CONNECT_FAILED;
}
setnonblocking(fd);
ses.maxfd = MAX(ses.maxfd, fd);
channel->readfd = fd;
channel->writefd = fd;
return 0;
}
/* Sends a request to the agent, returning a newly allocated buffer
* with the response */
/* This function will block waiting for a response - it will
* only be used by client authentication (not for forwarded requests)
* won't cause problems for interactivity. */
/* Packet format (from draft-ylonen)
4 bytes Length, msb first. Does not include length itself.
1 byte Packet type. The value 255 is reserved for future extensions.
data Any data, depending on packet type. Encoding as in the ssh packet
protocol.
*/
static buffer * agent_request(unsigned char type, const buffer *data) {
buffer * payload = NULL;
buffer * inbuf = NULL;
size_t readlen = 0;
ssize_t ret;
const int fd = cli_opts.agent_fd;
unsigned int data_len = 0;
if (data)
{
data_len = data->len;
}
payload = buf_new(4 + 1 + data_len);
buf_putint(payload, 1 + data_len);
buf_putbyte(payload, type);
if (data) {
buf_putbytes(payload, data->data, data->len);
}
buf_setpos(payload, 0);
ret = atomicio(vwrite, fd, buf_getptr(payload, payload->len), payload->len);
if ((size_t)ret != payload->len) {
TRACE(("write failed fd %d for agent_request, %s", fd, strerror(errno)))
goto out;
}
buf_free(payload);
payload = NULL;
TRACE(("Wrote out bytes for agent_request"))
/* Now we read the response */
inbuf = buf_new(4);
ret = atomicio(read, fd, buf_getwriteptr(inbuf, 4), 4);
if (ret != 4) {
TRACE(("read of length failed for agent_request"))
goto out;
}
buf_setpos(inbuf, 0);
buf_setlen(inbuf, ret);
readlen = buf_getint(inbuf);
if (readlen > MAX_AGENT_REPLY) {
TRACE(("agent reply is too big"));
goto out;
}
inbuf = buf_resize(inbuf, readlen);
buf_setpos(inbuf, 0);
ret = atomicio(read, fd, buf_getwriteptr(inbuf, readlen), readlen);
if ((size_t)ret != readlen) {
TRACE(("read of data failed for agent_request"))
goto out;
}
buf_incrwritepos(inbuf, readlen);
buf_setpos(inbuf, 0);
out:
if (payload)
buf_free(payload);
return inbuf;
}
static void agent_get_key_list(m_list * ret_list)
{
buffer * inbuf = NULL;
unsigned int num = 0;
unsigned char packet_type;
unsigned int i;
int ret;
inbuf = agent_request(SSH2_AGENTC_REQUEST_IDENTITIES, NULL);
if (!inbuf) {
TRACE(("agent_request failed returning identities"))
goto out;
}
/* The reply has a format of:
byte SSH2_AGENT_IDENTITIES_ANSWER
uint32 num_keys
Followed by zero or more consecutive keys, encoded as:
string key_blob
string key_comment
*/
packet_type = buf_getbyte(inbuf);
if (packet_type != SSH2_AGENT_IDENTITIES_ANSWER) {
goto out;
}
num = buf_getint(inbuf);
for (i = 0; i < num; i++) {
sign_key * pubkey = NULL;
enum signkey_type key_type = DROPBEAR_SIGNKEY_ANY;
buffer * key_buf;
/* each public key is encoded as a string */
key_buf = buf_getstringbuf(inbuf);
pubkey = new_sign_key();
ret = buf_get_pub_key(key_buf, pubkey, &key_type);
buf_free(key_buf);
if (ret != DROPBEAR_SUCCESS) {
TRACE(("Skipping bad/unknown type pubkey from agent"));
sign_key_free(pubkey);
} else {
pubkey->type = key_type;
pubkey->source = SIGNKEY_SOURCE_AGENT;
list_append(ret_list, pubkey);
}
/* We'll ignore the comment for now. might want it later.*/
buf_eatstring(inbuf);
}
out:
if (inbuf) {
buf_free(inbuf);
inbuf = NULL;
}
}
void cli_setup_agent(const struct Channel *channel) {
if (!getenv("SSH_AUTH_SOCK")) {
return;
}
start_send_channel_request(channel, "auth-agent-req@openssh.com");
/* Don't want replies */
buf_putbyte(ses.writepayload, 0);
encrypt_packet();
}
/* Returned keys are prepended to ret_list, which will
be updated. */
void cli_load_agent_keys(m_list *ret_list) {
/* agent_fd will be closed after successful auth */
cli_opts.agent_fd = connect_agent();
if (cli_opts.agent_fd < 0) {
return;
}
agent_get_key_list(ret_list);
}
void agent_buf_sign(buffer *sigblob, sign_key *key,
const buffer *data_buf) {
buffer *request_data = NULL;
buffer *response = NULL;
unsigned int siglen;
int packet_type;
/* Request format
byte SSH2_AGENTC_SIGN_REQUEST
string key_blob
string data
uint32 flags
*/
request_data = buf_new(MAX_PUBKEY_SIZE + data_buf->len + 12);
buf_put_pub_key(request_data, key, key->type);
buf_putbufstring(request_data, data_buf);
buf_putint(request_data, 0);
response = agent_request(SSH2_AGENTC_SIGN_REQUEST, request_data);
if (!response) {
goto fail;
}
packet_type = buf_getbyte(response);
if (packet_type != SSH2_AGENT_SIGN_RESPONSE) {
goto fail;
}
/* Response format
byte SSH2_AGENT_SIGN_RESPONSE
string signature_blob
*/
siglen = buf_getint(response);
buf_putbytes(sigblob, buf_getptr(response, siglen), siglen);
goto cleanup;
fail:
/* XXX don't fail badly here. instead propagate a failure code back up to
the cli auth pubkey code, and just remove this key from the list of
ones to try. */
dropbear_exit("Agent failed signing key");
cleanup:
if (request_data) {
buf_free(request_data);
}
if (response) {
buf_free(response);
}
}
#endif