/*
* Checks whether key is allowed in authorized_keys-format file,
* returns 1 if the key is allowed or 0 otherwise.
*/
static int
check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
{
char line[SSH_MAX_PUBKEY_BYTES];
const char *reason;
int found_key = 0;
u_long linenum = 0;
Key *found;
char *fp;
found_key = 0;
found = NULL;
while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
char *cp, *key_options = NULL;
if (found != NULL)
key_free(found);
found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
auth_clear_options();
/* Skip leading whitespace, empty and comment lines. */
for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
;
if (!*cp || *cp == '\n' || *cp == '#')
continue;
if (key_read(found, &cp) != 1) {
/* no key? check if there are options for this key */
int quoted = 0;
debug2("user_key_allowed: check options: '%s'", cp);
key_options = cp;
for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
if (*cp == '\\' && cp[1] == '"')
cp++; /* Skip both */
else if (*cp == '"')
quoted = !quoted;
}
/* Skip remaining whitespace. */
for (; *cp == ' ' || *cp == '\t'; cp++)
;
if (key_read(found, &cp) != 1) {
debug2("user_key_allowed: advance: '%s'", cp);
/* still no key? advance to next line*/
continue;
}
}
if (key_is_cert(key)) {
if (!key_equal(found, key->cert->signature_key))
continue;
if (auth_parse_options(pw, key_options, file,
linenum) != 1)
continue;
if (!key_is_cert_authority)
continue;
if ((fp = sshkey_fingerprint(found,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
continue;
debug("matching CA found: file %s, line %lu, %s %s",
file, linenum, key_type(found), fp);
/*
* If the user has specified a list of principals as
* a key option, then prefer that list to matching
* their username in the certificate principals list.
*/
if (authorized_principals != NULL &&
!match_principals_option(authorized_principals,
key->cert)) {
reason = "Certificate does not contain an "
"authorized principal";
fail_reason:
free(fp);
error("%s", reason);
auth_debug_add("%s", reason);
continue;
}
if (key_cert_check_authority(key, 0, 0,
authorized_principals == NULL ? pw->pw_name : NULL,
&reason) != 0)
goto fail_reason;
if (auth_cert_options(key, pw) != 0) {
free(fp);
continue;
}
verbose("Accepted certificate ID \"%s\" "
"signed by %s CA %s via %s", key->cert->key_id,
key_type(found), fp, file);
free(fp);
found_key = 1;
break;
} else if (key_equal(found, key)) {
if (auth_parse_options(pw, key_options, file,
linenum) != 1)
continue;
if (key_is_cert_authority)
continue;
if ((fp = sshkey_fingerprint(found,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
continue;
debug("matching key found: file %s, line %lu %s %s",
file, linenum, key_type(found), fp);
free(fp);
found_key = 1;
break;
}
}
if (found != NULL)
key_free(found);
if (!found_key)
debug2("key not found");
return found_key;
}
int
mm_answer_keyallowed(int sock, Buffer *m)
{
Key *key;
char *cuser, *chost;
u_char *blob;
u_int bloblen;
enum mm_keytype type = 0;
int allowed = 0;
debug3("%s entering", __func__);
type = buffer_get_int(m);
cuser = buffer_get_string(m, NULL);
chost = buffer_get_string(m, NULL);
blob = buffer_get_string(m, &bloblen);
key = key_from_blob(blob, bloblen);
if ((compat20 && type == MM_RSAHOSTKEY) ||
(!compat20 && type != MM_RSAHOSTKEY))
fatal("%s: key type and protocol mismatch", __func__);
debug3("%s: key_from_blob: %p", __func__, key);
if (key != NULL && authctxt->valid) {
switch (type) {
case MM_USERKEY:
allowed = options.pubkey_authentication &&
user_key_allowed(authctxt->pw, key);
auth_method = "publickey";
break;
case MM_HOSTKEY:
allowed = options.hostbased_authentication &&
hostbased_key_allowed(authctxt->pw,
cuser, chost, key);
auth_method = "hostbased";
break;
case MM_RSAHOSTKEY:
key->type = KEY_RSA1; /* XXX */
allowed = options.rhosts_rsa_authentication &&
auth_rhosts_rsa_key_allowed(authctxt->pw,
cuser, chost, key);
auth_method = "rsa";
break;
default:
fatal("%s: unknown key type %d", __func__, type);
break;
}
}
if (key != NULL)
key_free(key);
/* clear temporarily storage (used by verify) */
monitor_reset_key_state();
if (allowed) {
/* Save temporarily for comparison in verify */
key_blob = blob;
key_bloblen = bloblen;
key_blobtype = type;
hostbased_cuser = cuser;
hostbased_chost = chost;
} else {
/* Log failed attempt */
auth_log(authctxt, 0, auth_method, compat20 ? " ssh2" : "");
xfree(blob);
xfree(cuser);
xfree(chost);
}
debug3("%s: key %p is %s",
__func__, key, allowed ? "allowed" : "disallowed");
buffer_clear(m);
buffer_put_int(m, allowed);
buffer_put_int(m, forced_command != NULL);
mm_append_debug(m);
mm_request_send(sock, MONITOR_ANS_KEYALLOWED, m);
if (type == MM_RSAHOSTKEY)
monitor_permit(mon_dispatch, MONITOR_REQ_RSACHALLENGE, allowed);
return (0);
}
/*
* Checks if the user has an authentication agent, and if so, tries to
* authenticate using the agent.
*/
static int
try_agent_authentication(void)
{
int type;
char *comment;
AuthenticationConnection *auth;
u_char response[16];
u_int i;
Key *key;
BIGNUM *challenge;
/* Get connection to the agent. */
auth = ssh_get_authentication_connection();
if (!auth)
return 0;
if ((challenge = BN_new()) == NULL)
fatal("try_agent_authentication: BN_new failed");
/* Loop through identities served by the agent. */
for (key = ssh_get_first_identity(auth, &comment, 1);
key != NULL;
key = ssh_get_next_identity(auth, &comment, 1)) {
/* Try this identity. */
debug("Trying RSA authentication via agent with '%.100s'", comment);
xfree(comment);
/* Tell the server that we are willing to authenticate using this key. */
packet_start(SSH_CMSG_AUTH_RSA);
packet_put_bignum(key->rsa->n);
packet_send();
packet_write_wait();
/* Wait for server's response. */
type = packet_read();
/* 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.");
key_free(key);
continue;
}
/* Otherwise it should have sent a challenge. */
if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
packet_disconnect("Protocol error during RSA authentication: %d",
type);
packet_get_bignum(challenge);
packet_check_eom();
debug("Received RSA challenge from server.");
/* Ask the agent to decrypt the challenge. */
if (!ssh_decrypt_challenge(auth, key, challenge, session_id, 1, response)) {
/*
* The agent failed to authenticate this identifier
* although it advertised it supports this. Just
* return a wrong value.
*/
log("Authentication agent failed to decrypt challenge.");
memset(response, 0, sizeof(response));
}
key_free(key);
debug("Sending response to RSA challenge.");
/* Send the decrypted challenge back to the server. */
packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
for (i = 0; i < 16; i++)
packet_put_char(response[i]);
packet_send();
packet_write_wait();
/* Wait for response from the server. */
type = packet_read();
/* The server returns success if it accepted the authentication. */
if (type == SSH_SMSG_SUCCESS) {
ssh_close_authentication_connection(auth);
BN_clear_free(challenge);
debug("RSA authentication accepted by server.");
return 1;
}
/* Otherwise it should return failure. */
if (type != SSH_SMSG_FAILURE)
packet_disconnect("Protocol error waiting RSA auth response: %d",
type);
}
ssh_close_authentication_connection(auth);
BN_clear_free(challenge);
debug("RSA authentication using agent refused.");
return 0;
}
static int
valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
u_int datalen)
{
Buffer b;
Key *key = NULL;
u_char *pkblob;
u_int blen, len;
char *pkalg, *p;
int pktype, fail;
fail = 0;
buffer_init(&b);
buffer_append(&b, data, datalen);
/* session id, currently limited to SHA1 (20 bytes) */
p = buffer_get_string(&b, &len);
if (len != 20)
fail++;
xfree(p);
if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
fail++;
/* server user */
buffer_skip_string(&b);
/* service */
p = buffer_get_string(&b, NULL);
if (strcmp("ssh-connection", p) != 0)
fail++;
xfree(p);
/* method */
p = buffer_get_string(&b, NULL);
if (strcmp("hostbased", p) != 0)
fail++;
xfree(p);
/* pubkey */
pkalg = buffer_get_string(&b, NULL);
pkblob = buffer_get_string(&b, &blen);
pktype = key_type_from_name(pkalg);
if (pktype == KEY_UNSPEC)
fail++;
else if ((key = key_from_blob(pkblob, blen)) == NULL)
fail++;
else if (key->type != pktype)
fail++;
xfree(pkalg);
xfree(pkblob);
/* client host name, handle trailing dot */
p = buffer_get_string(&b, &len);
debug2("valid_request: check expect chost %s got %s", host, p);
if (strlen(host) != len - 1)
fail++;
else if (p[len - 1] != '.')
fail++;
else if (strncasecmp(host, p, len - 1) != 0)
fail++;
xfree(p);
/* local user */
p = buffer_get_string(&b, NULL);
if (strcmp(pw->pw_name, p) != 0)
fail++;
xfree(p);
/* end of message */
if (buffer_len(&b) != 0)
fail++;
buffer_free(&b);
debug3("valid_request: fail %d", fail);
if (fail && key != NULL)
key_free(key);
else
*ret = key;
return (fail ? -1 : 0);
}
static int
userauth_hostbased(Authctxt *authctxt)
{
Buffer b;
Key *key = NULL;
char *pkalg, *cuser, *chost, *service;
u_char *pkblob, *sig;
u_int alen, blen, slen;
int pktype;
int authenticated = 0;
if (!authctxt->valid) {
debug2("userauth_hostbased: disabled because of invalid user");
return 0;
}
pkalg = packet_get_string(&alen);
pkblob = packet_get_string(&blen);
chost = packet_get_string(NULL);
cuser = packet_get_string(NULL);
sig = packet_get_string(&slen);
debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
cuser, chost, pkalg, slen);
#ifdef DEBUG_PK
debug("signature:");
buffer_init(&b);
buffer_append(&b, sig, slen);
buffer_dump(&b);
buffer_free(&b);
#endif
pktype = key_type_from_name(pkalg);
if (pktype == KEY_UNSPEC) {
/* this is perfectly legal */
logit("userauth_hostbased: unsupported "
"public key algorithm: %s", pkalg);
goto done;
}
key = key_from_blob(pkblob, blen);
if (key == NULL) {
error("userauth_hostbased: cannot decode key: %s", pkalg);
goto done;
}
if (key->type != pktype) {
error("userauth_hostbased: type mismatch for decoded key "
"(received %d, expected %d)", key->type, pktype);
goto done;
}
service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
authctxt->service;
buffer_init(&b);
buffer_put_string(&b, session_id2, session_id2_len);
/* reconstruct packet */
buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
buffer_put_cstring(&b, authctxt->user);
buffer_put_cstring(&b, service);
buffer_put_cstring(&b, "hostbased");
buffer_put_string(&b, pkalg, alen);
buffer_put_string(&b, pkblob, blen);
buffer_put_cstring(&b, chost);
buffer_put_cstring(&b, cuser);
#ifdef DEBUG_PK
buffer_dump(&b);
#endif
pubkey_auth_info(authctxt, key,
"client user \"%.100s\", client host \"%.100s\"", cuser, chost);
/* test for allowed key and correct signature */
authenticated = 0;
if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
buffer_len(&b))) == 1)
authenticated = 1;
buffer_free(&b);
done:
debug2("userauth_hostbased: authenticated %d", authenticated);
if (key != NULL)
key_free(key);
free(pkalg);
free(pkblob);
free(cuser);
free(chost);
free(sig);
return authenticated;
}