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simplesshd/dropbear/svr-authpubkey.c
2014-12-10 16:56:49 -05:00

444 lines
13 KiB
C

/*
* Dropbear - a SSH2 server
*
* Copyright (c) 2002,2003 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. */
/*
* This file incorporates work covered by the following copyright and
* permission notice:
*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* This copyright and permission notice applies to the code parsing public keys
* options string which can also be found in OpenSSH auth2-pubkey.c file
* (user_key_allowed2). It has been adapted to work with buffers.
*
*/
/* Process a pubkey auth request */
#include "includes.h"
#include "session.h"
#include "dbutil.h"
#include "buffer.h"
#include "signkey.h"
#include "auth.h"
#include "ssh.h"
#include "packet.h"
#include "algo.h"
#ifdef ENABLE_SVR_PUBKEY_AUTH
#define MIN_AUTHKEYS_LINE 10 /* "ssh-rsa AB" - short but doesn't matter */
#define MAX_AUTHKEYS_LINE 4200 /* max length of a line in authkeys */
static int checkpubkey(unsigned char* algo, unsigned int algolen,
unsigned char* keyblob, unsigned int keybloblen);
static int checkpubkeyperms();
static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
unsigned char* keyblob, unsigned int keybloblen);
static int checkfileperm(char * filename);
/* process a pubkey auth request, sending success or failure message as
* appropriate */
void svr_auth_pubkey() {
unsigned char testkey; /* whether we're just checking if a key is usable */
unsigned char* algo = NULL; /* pubkey algo */
unsigned int algolen;
unsigned char* keyblob = NULL;
unsigned int keybloblen;
buffer * signbuf = NULL;
sign_key * key = NULL;
char* fp = NULL;
enum signkey_type type = -1;
TRACE(("enter pubkeyauth"))
/* 0 indicates user just wants to check if key can be used, 1 is an
* actual attempt*/
testkey = (buf_getbool(ses.payload) == 0);
algo = buf_getstring(ses.payload, &algolen);
keybloblen = buf_getint(ses.payload);
keyblob = buf_getptr(ses.payload, keybloblen);
/* check if the key is valid */
if (checkpubkey(algo, algolen, keyblob, keybloblen) == DROPBEAR_FAILURE) {
send_msg_userauth_failure(0, 0);
goto out;
}
/* let them know that the key is ok to use */
if (testkey) {
send_msg_userauth_pk_ok(algo, algolen, keyblob, keybloblen);
goto out;
}
/* now we can actually verify the signature */
/* get the key */
key = new_sign_key();
type = DROPBEAR_SIGNKEY_ANY;
if (buf_get_pub_key(ses.payload, key, &type) == DROPBEAR_FAILURE) {
send_msg_userauth_failure(0, 1);
goto out;
}
/* create the data which has been signed - this a string containing
* session_id, concatenated with the payload packet up to the signature */
signbuf = buf_new(ses.payload->pos + 4 + ses.session_id->len);
buf_putbufstring(signbuf, ses.session_id);
buf_putbytes(signbuf, ses.payload->data, ses.payload->pos);
buf_setpos(signbuf, 0);
/* ... and finally verify the signature */
fp = sign_key_fingerprint(keyblob, keybloblen);
if (buf_verify(ses.payload, key, signbuf) == DROPBEAR_SUCCESS) {
dropbear_log(LOG_NOTICE,
"Pubkey auth succeeded for '%s' with key %s from %s",
ses.authstate.pw_name, fp, svr_ses.addrstring);
send_msg_userauth_success();
} else {
dropbear_log(LOG_WARNING,
"Pubkey auth bad signature for '%s' with key %s from %s",
ses.authstate.pw_name, fp, svr_ses.addrstring);
send_msg_userauth_failure(0, 1);
}
m_free(fp);
out:
/* cleanup stuff */
if (signbuf) {
buf_free(signbuf);
}
if (algo) {
m_free(algo);
}
if (key) {
sign_key_free(key);
key = NULL;
}
TRACE(("leave pubkeyauth"))
}
/* Reply that the key is valid for auth, this is sent when the user sends
* a straight copy of their pubkey to test, to avoid having to perform
* expensive signing operations with a worthless key */
static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
unsigned char* keyblob, unsigned int keybloblen) {
TRACE(("enter send_msg_userauth_pk_ok"))
CHECKCLEARTOWRITE();
buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_PK_OK);
buf_putstring(ses.writepayload, algo, algolen);
buf_putstring(ses.writepayload, keyblob, keybloblen);
encrypt_packet();
TRACE(("leave send_msg_userauth_pk_ok"))
}
/* Checks whether a specified publickey (and associated algorithm) is an
* acceptable key for authentication */
/* Returns DROPBEAR_SUCCESS if key is ok for auth, DROPBEAR_FAILURE otherwise */
static int checkpubkey(unsigned char* algo, unsigned int algolen,
unsigned char* keyblob, unsigned int keybloblen) {
FILE * authfile = NULL;
char * filename = NULL;
int ret = DROPBEAR_FAILURE;
buffer * line = NULL;
unsigned int len, pos;
buffer * options_buf = NULL;
int line_num;
TRACE(("enter checkpubkey"))
/* check that we can use the algo */
if (have_algo(algo, algolen, sshhostkey) == DROPBEAR_FAILURE) {
dropbear_log(LOG_WARNING,
"Pubkey auth attempt with unknown algo for '%s' from %s",
ses.authstate.pw_name, svr_ses.addrstring);
goto out;
}
/* check file permissions, also whether file exists */
if (checkpubkeyperms() == DROPBEAR_FAILURE) {
TRACE(("bad authorized_keys permissions, or file doesn't exist"))
goto out;
}
/* we don't need to check pw and pw_dir for validity, since
* its been done in checkpubkeyperms. */
len = strlen(ses.authstate.pw_dir);
/* allocate max required pathname storage,
* = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
filename = m_malloc(len + 22);
snprintf(filename, len + 22, "%s/.ssh/authorized_keys",
ses.authstate.pw_dir);
/* open the file */
authfile = fopen(filename, "r");
if (authfile == NULL) {
goto out;
}
TRACE(("checkpubkey: opened authorized_keys OK"))
line = buf_new(MAX_AUTHKEYS_LINE);
line_num = 0;
/* iterate through the lines */
do {
/* new line : potentially new options */
if (options_buf) {
buf_free(options_buf);
options_buf = NULL;
}
if (buf_getline(line, authfile) == DROPBEAR_FAILURE) {
/* EOF reached */
TRACE(("checkpubkey: authorized_keys EOF reached"))
break;
}
line_num++;
if (line->len < MIN_AUTHKEYS_LINE) {
TRACE(("checkpubkey: line too short"))
continue; /* line is too short for it to be a valid key */
}
/* check the key type - will fail if there are options */
TRACE(("a line!"))
if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
int is_comment = 0;
char *options_start = NULL;
int options_len = 0;
int escape, quoted;
/* skip over any comments or leading whitespace */
while (line->pos < line->len) {
const char c = buf_getbyte(line);
if (c == ' ' || c == '\t') {
continue;
} else if (c == '#') {
is_comment = 1;
break;
}
buf_incrpos(line, -1);
break;
}
if (is_comment) {
/* next line */
continue;
}
/* remember start of options */
options_start = buf_getptr(line, 1);
quoted = 0;
escape = 0;
options_len = 0;
/* figure out where the options are */
while (line->pos < line->len) {
const char c = buf_getbyte(line);
if (!quoted && (c == ' ' || c == '\t')) {
break;
}
escape = (!escape && c == '\\');
if (!escape && c == '"') {
quoted = !quoted;
}
options_len++;
}
options_buf = buf_new(options_len);
buf_putbytes(options_buf, options_start, options_len);
/* compare the algorithm. +3 so we have enough bytes to read a space and some base64 characters too. */
if (line->pos + algolen+3 > line->len) {
continue;
}
if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
continue;
}
}
buf_incrpos(line, algolen);
/* check for space (' ') character */
if (buf_getbyte(line) != ' ') {
TRACE(("checkpubkey: space character expected, isn't there"))
continue;
}
/* truncate the line at the space after the base64 data */
pos = line->pos;
for (len = 0; line->pos < line->len; len++) {
if (buf_getbyte(line) == ' ') break;
}
buf_setpos(line, pos);
buf_setlen(line, line->pos + len);
TRACE(("checkpubkey: line pos = %d len = %d", line->pos, line->len))
ret = cmp_base64_key(keyblob, keybloblen, algo, algolen, line, NULL);
if (ret == DROPBEAR_SUCCESS && options_buf) {
ret = svr_add_pubkey_options(options_buf, line_num, filename);
}
if (ret == DROPBEAR_SUCCESS) {
break;
}
/* We continue to the next line otherwise */
} while (1);
out:
if (authfile) {
fclose(authfile);
}
if (line) {
buf_free(line);
}
m_free(filename);
if (options_buf) {
buf_free(options_buf);
}
TRACE(("leave checkpubkey: ret=%d", ret))
return ret;
}
/* Returns DROPBEAR_SUCCESS if file permissions for pubkeys are ok,
* DROPBEAR_FAILURE otherwise.
* Checks that the user's homedir, ~/.ssh, and
* ~/.ssh/authorized_keys are all owned by either root or the user, and are
* g-w, o-w */
static int checkpubkeyperms() {
char* filename = NULL;
int ret = DROPBEAR_FAILURE;
unsigned int len;
TRACE(("enter checkpubkeyperms"))
if (ses.authstate.pw_dir == NULL) {
goto out;
}
if ((len = strlen(ses.authstate.pw_dir)) == 0) {
goto out;
}
/* allocate max required pathname storage,
* = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
filename = m_malloc(len + 22);
strncpy(filename, ses.authstate.pw_dir, len+1);
/* check ~ */
if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
goto out;
}
/* check ~/.ssh */
strncat(filename, "/.ssh", 5); /* strlen("/.ssh") == 5 */
if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
goto out;
}
/* now check ~/.ssh/authorized_keys */
strncat(filename, "/authorized_keys", 16);
if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
goto out;
}
/* file looks ok, return success */
ret = DROPBEAR_SUCCESS;
out:
m_free(filename);
TRACE(("leave checkpubkeyperms"))
return ret;
}
/* Checks that a file is owned by the user or root, and isn't writable by
* group or other */
/* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
static int checkfileperm(char * filename) {
struct stat filestat;
int badperm = 0;
TRACE(("enter checkfileperm(%s)", filename))
if (stat(filename, &filestat) != 0) {
TRACE(("leave checkfileperm: stat() != 0"))
return DROPBEAR_FAILURE;
}
/* check ownership - user or root only*/
if (filestat.st_uid != ses.authstate.pw_uid
&& filestat.st_uid != 0) {
badperm = 1;
TRACE(("wrong ownership"))
}
/* check permissions - don't want group or others +w */
if (filestat.st_mode & (S_IWGRP | S_IWOTH)) {
badperm = 1;
TRACE(("wrong perms"))
}
if (badperm) {
if (!ses.authstate.perm_warn) {
ses.authstate.perm_warn = 1;
dropbear_log(LOG_INFO, "%s must be owned by user or root, and not writable by others", filename);
}
TRACE(("leave checkfileperm: failure perms/owner"))
return DROPBEAR_FAILURE;
}
TRACE(("leave checkfileperm: success"))
return DROPBEAR_SUCCESS;
}
#endif