X-Git-Url: http://andersk.mit.edu/gitweb/openssh.git/blobdiff_plain/2d4e8a879ffa6f70cdcfd58bbdd0a5fa775c3205..52e1856c61223b4df9953eb2c185dbc38f0d319c:/auth-rsa.c diff --git a/auth-rsa.c b/auth-rsa.c index 86aa72de..bf546207 100644 --- a/auth-rsa.c +++ b/auth-rsa.c @@ -1,487 +1,324 @@ +/* $OpenBSD: auth-rsa.c,v 1.73 2008/07/02 12:03:51 dtucker Exp $ */ /* + * Author: Tatu Ylonen + * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland + * All rights reserved + * RSA-based authentication. This code determines whether to admit a login + * based on RSA authentication. This file also contains functions to check + * validity of the host key. + * + * As far as I am concerned, the code I have written for this software + * can be used freely for any purpose. Any derived versions of this + * software must be clearly marked as such, and if the derived work is + * incompatible with the protocol description in the RFC file, it must be + * called by a name other than "ssh" or "Secure Shell". + */ -auth-rsa.c - -Author: Tatu Ylonen - -Copyright (c) 1995 Tatu Ylonen , Espoo, Finland - All rights reserved - -Created: Mon Mar 27 01:46:52 1995 ylo +#include "includes.h" -RSA-based authentication. This code determines whether to admit a login -based on RSA authentication. This file also contains functions to check -validity of the host key. +#include +#include -*/ +#include +#include -#include "includes.h" -RCSID("$Id$"); +#include +#include +#include +#include +#include "xmalloc.h" #include "rsa.h" #include "packet.h" -#include "xmalloc.h" -#include "ssh.h" -#include "mpaux.h" +#include "ssh1.h" #include "uidswap.h" +#include "match.h" +#include "buffer.h" +#include "auth-options.h" +#include "pathnames.h" +#include "log.h" #include "servconf.h" - -#ifdef HAVE_OPENSSL -#include -#include -#endif -#ifdef HAVE_SSL -#include -#include +#include "key.h" +#include "hostfile.h" +#include "auth.h" +#ifdef GSSAPI +#include "ssh-gss.h" #endif +#include "monitor_wrap.h" +#include "ssh.h" +#include "misc.h" -/* Flags that may be set in authorized_keys options. */ -extern int no_port_forwarding_flag; -extern int no_agent_forwarding_flag; -extern int no_x11_forwarding_flag; -extern int no_pty_flag; -extern char *forced_command; -extern struct envstring *custom_environment; - -/* Session identifier that is used to bind key exchange and authentication - responses to a particular session. */ -extern unsigned char session_id[16]; - -/* The .ssh/authorized_keys file contains public keys, one per line, in the - following format: - options bits e n comment - where bits, e and n are decimal numbers, - and comment is any string of characters up to newline. The maximum - length of a line is 8000 characters. See the documentation for a - description of the options. -*/ - -/* Performs the RSA authentication challenge-response dialog with the client, - and returns true (non-zero) if the client gave the correct answer to - our challenge; returns zero if the client gives a wrong answer. */ +/* import */ +extern ServerOptions options; -int -auth_rsa_challenge_dialog(unsigned int bits, BIGNUM *e, BIGNUM *n) +/* + * Session identifier that is used to bind key exchange and authentication + * responses to a particular session. + */ +extern u_char session_id[16]; + +/* + * The .ssh/authorized_keys file contains public keys, one per line, in the + * following format: + * options bits e n comment + * where bits, e and n are decimal numbers, + * and comment is any string of characters up to newline. The maximum + * length of a line is SSH_MAX_PUBKEY_BYTES characters. See sshd(8) for a + * description of the options. + */ + +BIGNUM * +auth_rsa_generate_challenge(Key *key) { - BIGNUM *challenge, *encrypted_challenge, *aux; - RSA *pk; - BN_CTX *ctx = BN_CTX_new(); - unsigned char buf[32], mdbuf[16], response[16]; - MD5_CTX md; - unsigned int i; - int plen, len; - - encrypted_challenge = BN_new(); - challenge = BN_new(); - aux = BN_new(); - - /* Generate a random challenge. */ - BN_rand(challenge, 256, 0, 0); - BN_mod(challenge, challenge, n, ctx); - - /* Create the public key data structure. */ - pk = RSA_new(); - pk->e = BN_new(); - BN_copy(pk->e, e); - pk->n = BN_new(); - BN_copy(pk->n, n); - - /* Encrypt the challenge with the public key. */ - rsa_public_encrypt(encrypted_challenge, challenge, pk); - RSA_free(pk); - - /* Send the encrypted challenge to the client. */ - packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE); - packet_put_bignum(encrypted_challenge); - packet_send(); - packet_write_wait(); - - /* The response is MD5 of decrypted challenge plus session id. */ - len = BN_num_bytes(challenge); - if (len <= 0 || len > 32) - fatal("auth_rsa_challenge_dialog: bad challenge length %d", len); - memset(buf, 0, 32); - BN_bn2bin(challenge, buf + 32 - len); - MD5_Init(&md); - MD5_Update(&md, buf, 32); - MD5_Update(&md, session_id, 16); - MD5_Final(mdbuf, &md); - - /* We will no longer need these. */ - BN_clear_free(encrypted_challenge); - BN_clear_free(challenge); - BN_clear_free(aux); - BN_CTX_free(ctx); - - /* Wait for a response. */ - packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE); - packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE); - for (i = 0; i < 16; i++) - response[i] = packet_get_char(); - - /* Verify that the response is the original challenge. */ - if (memcmp(response, mdbuf, 16) != 0) - { - /* Wrong answer. */ - return 0; - } - - /* Correct answer. */ - return 1; + BIGNUM *challenge; + BN_CTX *ctx; + + if ((challenge = BN_new()) == NULL) + fatal("auth_rsa_generate_challenge: BN_new() failed"); + /* Generate a random challenge. */ + if (BN_rand(challenge, 256, 0, 0) == 0) + fatal("auth_rsa_generate_challenge: BN_rand failed"); + if ((ctx = BN_CTX_new()) == NULL) + fatal("auth_rsa_generate_challenge: BN_CTX_new failed"); + if (BN_mod(challenge, challenge, key->rsa->n, ctx) == 0) + fatal("auth_rsa_generate_challenge: BN_mod failed"); + BN_CTX_free(ctx); + + return challenge; } -/* Performs the RSA authentication dialog with the client. This returns - 0 if the client could not be authenticated, and 1 if authentication was - successful. This may exit if there is a serious protocol violation. */ - int -auth_rsa(struct passwd *pw, BIGNUM *client_n) +auth_rsa_verify_response(Key *key, BIGNUM *challenge, u_char response[16]) { - extern ServerOptions options; - char line[8192]; - int authenticated; - unsigned int bits; - FILE *f; - unsigned long linenum = 0; - struct stat st; - BIGNUM *e, *n; - - /* Temporarily use the user's uid. */ - temporarily_use_uid(pw->pw_uid); - - /* The authorized keys. */ - snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, - SSH_USER_PERMITTED_KEYS); - - /* Fail quietly if file does not exist */ - if (stat(line, &st) < 0) - { - /* Restore the privileged uid. */ - restore_uid(); - return 0; - } - - /* Open the file containing the authorized keys. */ - f = fopen(line, "r"); - if (!f) - { - /* Restore the privileged uid. */ - restore_uid(); - packet_send_debug("Could not open %.900s for reading.", line); - packet_send_debug("If your home is on an NFS volume, it may need to be world-readable."); - return 0; - } - - if (options.strict_modes) { - int fail=0; - char buf[1024]; - /* Check open file in order to avoid open/stat races */ - if (fstat(fileno(f), &st) < 0 || - (st.st_uid != 0 && st.st_uid != pw->pw_uid) || - (st.st_mode & 022) != 0) { - snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " - "bad ownership or modes for '%s'.", pw->pw_name, line); - fail=1; - }else{ - /* Check path to SSH_USER_PERMITTED_KEYS */ - int i; - static const char *check[] = { - "", SSH_USER_DIR, NULL - }; - for (i=0; check[i]; i++) { - snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]); - if (stat(line, &st) < 0 || - (st.st_uid != 0 && st.st_uid != pw->pw_uid) || - (st.st_mode & 022) != 0) { - snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " - "bad ownership or modes for '%s'.", pw->pw_name, line); - fail=1; - break; - } - } - } - if (fail) { - log(buf); - packet_send_debug(buf); - restore_uid(); - return 0; - } - } - - /* Flag indicating whether authentication has succeeded. */ - authenticated = 0; - - /* Initialize mp-int variables. */ - e = BN_new(); - n = BN_new(); - - /* Go though the accepted keys, looking for the current key. If found, - perform a challenge-response dialog to verify that the user really has - the corresponding private key. */ - while (fgets(line, sizeof(line), f)) - { - char *cp; - char *options; - - linenum++; - - /* Skip leading whitespace. */ - for (cp = line; *cp == ' ' || *cp == '\t'; cp++) - ; - - /* Skip empty and comment lines. */ - if (!*cp || *cp == '\n' || *cp == '#') - continue; - - /* Check if there are options for this key, and if so, save their - starting address and skip the option part for now. If there are no - options, set the starting address to NULL. */ - if (*cp < '0' || *cp > '9') - { - int quoted = 0; - options = cp; - for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) - { - if (*cp == '\\' && cp[1] == '"') - cp++; /* Skip both */ - else - if (*cp == '"') - quoted = !quoted; - } + u_char buf[32], mdbuf[16]; + MD5_CTX md; + int len; + + /* don't allow short keys */ + if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) { + error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits", + BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE); + return (0); } - else - options = NULL; - - /* Parse the key from the line. */ - if (!auth_rsa_read_key(&cp, &bits, e, n)) - { - debug("%.100s, line %lu: bad key syntax", - SSH_USER_PERMITTED_KEYS, linenum); - packet_send_debug("%.100s, line %lu: bad key syntax", - SSH_USER_PERMITTED_KEYS, linenum); - continue; + + /* The response is MD5 of decrypted challenge plus session id. */ + len = BN_num_bytes(challenge); + if (len <= 0 || len > 32) + fatal("auth_rsa_verify_response: bad challenge length %d", len); + memset(buf, 0, 32); + BN_bn2bin(challenge, buf + 32 - len); + MD5_Init(&md); + MD5_Update(&md, buf, 32); + MD5_Update(&md, session_id, 16); + MD5_Final(mdbuf, &md); + + /* Verify that the response is the original challenge. */ + if (memcmp(response, mdbuf, 16) != 0) { + /* Wrong answer. */ + return (0); } - /* cp now points to the comment part. */ - - /* Check if the we have found the desired key (identified by its - modulus). */ - if (BN_cmp(n, client_n) != 0) - continue; /* Wrong key. */ - - /* We have found the desired key. */ - - /* Perform the challenge-response dialog for this key. */ - if (!auth_rsa_challenge_dialog(bits, e, n)) - { - /* Wrong response. */ - log("Wrong response to RSA authentication challenge."); - packet_send_debug("Wrong response to RSA authentication challenge."); - continue; + /* Correct answer. */ + return (1); +} + +/* + * Performs the RSA authentication challenge-response dialog with the client, + * and returns true (non-zero) if the client gave the correct answer to + * our challenge; returns zero if the client gives a wrong answer. + */ + +int +auth_rsa_challenge_dialog(Key *key) +{ + BIGNUM *challenge, *encrypted_challenge; + u_char response[16]; + int i, success; + + if ((encrypted_challenge = BN_new()) == NULL) + fatal("auth_rsa_challenge_dialog: BN_new() failed"); + + challenge = PRIVSEP(auth_rsa_generate_challenge(key)); + + /* Encrypt the challenge with the public key. */ + rsa_public_encrypt(encrypted_challenge, challenge, key->rsa); + + /* Send the encrypted challenge to the client. */ + packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE); + packet_put_bignum(encrypted_challenge); + packet_send(); + BN_clear_free(encrypted_challenge); + packet_write_wait(); + + /* Wait for a response. */ + packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE); + for (i = 0; i < 16; i++) + response[i] = (u_char)packet_get_char(); + packet_check_eom(); + + success = PRIVSEP(auth_rsa_verify_response(key, challenge, response)); + BN_clear_free(challenge); + return (success); +} + +/* + * check if there's user key matching client_n, + * return key if login is allowed, NULL otherwise + */ + +int +auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey) +{ + char line[SSH_MAX_PUBKEY_BYTES], *file; + int allowed = 0; + u_int bits; + FILE *f; + u_long linenum = 0; + Key *key; + + /* Temporarily use the user's uid. */ + temporarily_use_uid(pw); + + /* The authorized keys. */ + file = authorized_keys_file(pw); + debug("trying public RSA key file %s", file); + f = auth_openkeyfile(file, pw, options.strict_modes); + if (!f) { + xfree(file); + restore_uid(); + return (0); } - /* Correct response. The client has been successfully authenticated. - Note that we have not yet processed the options; this will be reset - if the options cause the authentication to be rejected. */ - authenticated = 1; - - /* RSA part of authentication was accepted. Now process the options. */ - if (options) - { - while (*options && *options != ' ' && *options != '\t') - { - cp = "no-port-forwarding"; - if (strncmp(options, cp, strlen(cp)) == 0) - { - packet_send_debug("Port forwarding disabled."); - no_port_forwarding_flag = 1; - options += strlen(cp); - goto next_option; - } - cp = "no-agent-forwarding"; - if (strncmp(options, cp, strlen(cp)) == 0) - { - packet_send_debug("Agent forwarding disabled."); - no_agent_forwarding_flag = 1; - options += strlen(cp); - goto next_option; - } - cp = "no-X11-forwarding"; - if (strncmp(options, cp, strlen(cp)) == 0) - { - packet_send_debug("X11 forwarding disabled."); - no_x11_forwarding_flag = 1; - options += strlen(cp); - goto next_option; - } - cp = "no-pty"; - if (strncmp(options, cp, strlen(cp)) == 0) - { - packet_send_debug("Pty allocation disabled."); - no_pty_flag = 1; - options += strlen(cp); - goto next_option; - } - cp = "command=\""; - if (strncmp(options, cp, strlen(cp)) == 0) - { - int i; - options += strlen(cp); - forced_command = xmalloc(strlen(options) + 1); - i = 0; - while (*options) - { - if (*options == '"') - break; - if (*options == '\\' && options[1] == '"') - { - options += 2; - forced_command[i++] = '"'; - continue; + /* Flag indicating whether the key is allowed. */ + allowed = 0; + + key = key_new(KEY_RSA1); + + /* + * Go though the accepted keys, looking for the current key. If + * found, perform a challenge-response dialog to verify that the + * user really has the corresponding private key. + */ + while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { + char *cp; + char *key_options; + int keybits; + + /* Skip leading whitespace, empty and comment lines. */ + for (cp = line; *cp == ' ' || *cp == '\t'; cp++) + ; + if (!*cp || *cp == '\n' || *cp == '#') + continue; + + /* + * Check if there are options for this key, and if so, + * save their starting address and skip the option part + * for now. If there are no options, set the starting + * address to NULL. + */ + if (*cp < '0' || *cp > '9') { + int quoted = 0; + key_options = cp; + for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { + if (*cp == '\\' && cp[1] == '"') + cp++; /* Skip both */ + else if (*cp == '"') + quoted = !quoted; } - forced_command[i++] = *options++; - } - if (!*options) - { - debug("%.100s, line %lu: missing end quote", - SSH_USER_PERMITTED_KEYS, linenum); - packet_send_debug("%.100s, line %lu: missing end quote", - SSH_USER_PERMITTED_KEYS, linenum); - continue; - } - forced_command[i] = 0; - packet_send_debug("Forced command: %.900s", forced_command); - options++; - goto next_option; + } else + key_options = NULL; + + /* Parse the key from the line. */ + if (hostfile_read_key(&cp, &bits, key) == 0) { + debug("%.100s, line %lu: non ssh1 key syntax", + file, linenum); + continue; } - cp = "environment=\""; - if (strncmp(options, cp, strlen(cp)) == 0) - { - int i; - char *s; - struct envstring *new_envstring; - options += strlen(cp); - s = xmalloc(strlen(options) + 1); - i = 0; - while (*options) - { - if (*options == '"') - break; - if (*options == '\\' && options[1] == '"') - { - options += 2; - s[i++] = '"'; - continue; - } - s[i++] = *options++; - } - if (!*options) - { - debug("%.100s, line %lu: missing end quote", - SSH_USER_PERMITTED_KEYS, linenum); - packet_send_debug("%.100s, line %lu: missing end quote", - SSH_USER_PERMITTED_KEYS, linenum); - continue; - } - s[i] = 0; - packet_send_debug("Adding to environment: %.900s", s); - debug("Adding to environment: %.900s", s); - options++; - new_envstring = xmalloc(sizeof(struct envstring)); - new_envstring->s = s; - new_envstring->next = custom_environment; - custom_environment = new_envstring; - goto next_option; - } - cp = "from=\""; - if (strncmp(options, cp, strlen(cp)) == 0) - { - char *patterns = xmalloc(strlen(options) + 1); - int i; - options += strlen(cp); - i = 0; - while (*options) - { - if (*options == '"') - break; - if (*options == '\\' && options[1] == '"') - { - options += 2; - patterns[i++] = '"'; - continue; - } - patterns[i++] = *options++; - } - if (!*options) - { - debug("%.100s, line %lu: missing end quote", - SSH_USER_PERMITTED_KEYS, linenum); - packet_send_debug("%.100s, line %lu: missing end quote", - SSH_USER_PERMITTED_KEYS, linenum); - continue; - } - patterns[i] = 0; - options++; - if (!match_hostname(get_canonical_hostname(), patterns, - strlen(patterns)) && - !match_hostname(get_remote_ipaddr(), patterns, - strlen(patterns))) - { - log("RSA authentication tried for %.100s with correct key but not from a permitted host (host=%.200s, ip=%.200s).", - pw->pw_name, get_canonical_hostname(), - get_remote_ipaddr()); - packet_send_debug("Your host '%.200s' is not permitted to use this key for login.", - get_canonical_hostname()); - xfree(patterns); - authenticated = 0; - break; - } - xfree(patterns); - /* Host name matches. */ - goto next_option; - } - bad_option: - /* Unknown option. */ - log("Bad options in %.100s file, line %lu: %.50s", - SSH_USER_PERMITTED_KEYS, linenum, options); - packet_send_debug("Bad options in %.100s file, line %lu: %.50s", - SSH_USER_PERMITTED_KEYS, linenum, options); - authenticated = 0; - break; - - next_option: - /* Skip the comma, and move to the next option (or break out - if there are no more). */ - if (!*options) - fatal("Bugs in auth-rsa.c option processing."); - if (*options == ' ' || *options == '\t') - break; /* End of options. */ - if (*options != ',') - goto bad_option; - options++; - /* Process the next option. */ - continue; - } + /* cp now points to the comment part. */ + + /* Check if the we have found the desired key (identified by its modulus). */ + if (BN_cmp(key->rsa->n, client_n) != 0) + continue; + + /* check the real bits */ + keybits = BN_num_bits(key->rsa->n); + if (keybits < 0 || bits != (u_int)keybits) + logit("Warning: %s, line %lu: keysize mismatch: " + "actual %d vs. announced %d.", + file, linenum, BN_num_bits(key->rsa->n), bits); + + /* We have found the desired key. */ + /* + * If our options do not allow this key to be used, + * do not send challenge. + */ + if (!auth_parse_options(pw, key_options, file, linenum)) + continue; + + /* break out, this key is allowed */ + allowed = 1; + break; } - /* Break out of the loop if authentication was successful; otherwise - continue searching. */ - if (authenticated) - break; - } + /* Restore the privileged uid. */ + restore_uid(); + + /* Close the file. */ + xfree(file); + fclose(f); + + /* return key if allowed */ + if (allowed && rkey != NULL) + *rkey = key; + else + key_free(key); + return (allowed); +} - /* Restore the privileged uid. */ - restore_uid(); +/* + * Performs the RSA authentication dialog with the client. This returns + * 0 if the client could not be authenticated, and 1 if authentication was + * successful. This may exit if there is a serious protocol violation. + */ +int +auth_rsa(Authctxt *authctxt, BIGNUM *client_n) +{ + Key *key; + char *fp; + struct passwd *pw = authctxt->pw; - /* Close the file. */ - fclose(f); - - /* Clear any mp-int variables. */ - BN_clear_free(n); - BN_clear_free(e); + /* no user given */ + if (!authctxt->valid) + return 0; - if (authenticated) - packet_send_debug("RSA authentication accepted."); + if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) { + auth_clear_options(); + return (0); + } - /* Return authentication result. */ - return authenticated; + /* Perform the challenge-response dialog for this key. */ + if (!auth_rsa_challenge_dialog(key)) { + /* Wrong response. */ + verbose("Wrong response to RSA authentication challenge."); + packet_send_debug("Wrong response to RSA authentication challenge."); + /* + * Break out of the loop. Otherwise we might send + * another challenge and break the protocol. + */ + key_free(key); + return (0); + } + /* + * Correct response. The client has been successfully + * authenticated. Note that we have not yet processed the + * options; this will be reset if the options cause the + * authentication to be rejected. + */ + fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); + verbose("Found matching %s key: %s", + key_type(key), fp); + xfree(fp); + key_free(key); + + packet_send_debug("RSA authentication accepted."); + return (1); }