| /* |
| * 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. */ |
| |
| /* 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.printableuser, 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.printableuser, 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; |
| |
| 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.printableuser, 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->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->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); |
| |
| /* iterate through the lines */ |
| do { |
| |
| if (buf_getline(line, authfile) == DROPBEAR_FAILURE) { |
| /* EOF reached */ |
| TRACE(("checkpubkey: authorized_keys EOF reached")) |
| break; |
| } |
| |
| 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 - this also stops us from using keys |
| * which have options with them */ |
| 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) { |
| break; |
| } |
| |
| /* We continue to the next line otherwise */ |
| |
| } while (1); |
| |
| out: |
| if (authfile) { |
| fclose(authfile); |
| } |
| if (line) { |
| buf_free(line); |
| } |
| m_free(filename); |
| 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->pw_dir == NULL) { |
| goto out; |
| } |
| |
| if ((len = strlen(ses.authstate.pw->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->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->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 |