usbmodeswitch: Updated to v.1.2.6 from shibby's branch.

[tomato.git] / release / src / router / dropbear / svr-authpubkey.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;
        int 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 + SHA1_HASH_SIZE);
        buf_putstring(signbuf, ses.session_id, SHA1_HASH_SIZE);
        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, buf_getptr(signbuf, signbuf->len),
                                signbuf->len) == 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 */
                        if (line->pos + algolen > 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