| /* |
| * |
| * auth-rsa.c |
| * |
| * Author: Tatu Ylonen <ylo@cs.hut.fi> |
| * |
| * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| * All rights reserved |
| * |
| * Created: Mon Mar 27 01:46:52 1995 ylo |
| * |
| * 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 "includes.h" |
| RCSID("$Id: auth-rsa.c,v 1.18 2000/04/29 13:57:09 damien Exp $"); |
| |
| #include "rsa.h" |
| #include "packet.h" |
| #include "xmalloc.h" |
| #include "ssh.h" |
| #include "mpaux.h" |
| #include "uidswap.h" |
| #include "match.h" |
| #include "servconf.h" |
| |
| #include <openssl/rsa.h> |
| #include <openssl/md5.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. |
| */ |
| |
| int |
| auth_rsa_challenge_dialog(RSA *pk) |
| { |
| BIGNUM *challenge, *encrypted_challenge; |
| BN_CTX *ctx; |
| unsigned char buf[32], mdbuf[16], response[16]; |
| MD5_CTX md; |
| unsigned int i; |
| int plen, len; |
| |
| encrypted_challenge = BN_new(); |
| challenge = BN_new(); |
| |
| /* Generate a random challenge. */ |
| BN_rand(challenge, 256, 0, 0); |
| ctx = BN_CTX_new(); |
| BN_mod(challenge, challenge, pk->n, ctx); |
| BN_CTX_free(ctx); |
| |
| /* Encrypt the challenge with the public key. */ |
| rsa_public_encrypt(encrypted_challenge, challenge, pk); |
| |
| /* 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(&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(); |
| |
| /* 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); |
| BN_clear_free(challenge); |
| |
| /* Verify that the response is the original challenge. */ |
| if (memcmp(response, mdbuf, 16) != 0) { |
| /* Wrong answer. */ |
| return 0; |
| } |
| /* Correct answer. */ |
| return 1; |
| } |
| |
| /* |
| * 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) |
| { |
| extern ServerOptions options; |
| char line[8192], file[1024]; |
| int authenticated; |
| unsigned int bits; |
| FILE *f; |
| unsigned long linenum = 0; |
| struct stat st; |
| RSA *pk; |
| |
| /* Temporarily use the user's uid. */ |
| temporarily_use_uid(pw->pw_uid); |
| |
| /* The authorized keys. */ |
| snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir, |
| SSH_USER_PERMITTED_KEYS); |
| |
| /* Fail quietly if file does not exist */ |
| if (stat(file, &st) < 0) { |
| /* Restore the privileged uid. */ |
| restore_uid(); |
| return 0; |
| } |
| /* Open the file containing the authorized keys. */ |
| f = fopen(file, "r"); |
| if (!f) { |
| /* Restore the privileged uid. */ |
| restore_uid(); |
| packet_send_debug("Could not open %.900s for reading.", file); |
| 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, file); |
| 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) { |
| fclose(f); |
| log(buf); |
| packet_send_debug(buf); |
| restore_uid(); |
| return 0; |
| } |
| } |
| /* Flag indicating whether authentication has succeeded. */ |
| authenticated = 0; |
| |
| pk = RSA_new(); |
| pk->e = BN_new(); |
| pk->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, 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; |
| options = cp; |
| for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { |
| if (*cp == '\\' && cp[1] == '"') |
| cp++; /* Skip both */ |
| else if (*cp == '"') |
| quoted = !quoted; |
| } |
| } else |
| options = NULL; |
| |
| /* Parse the key from the line. */ |
| if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->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; |
| } |
| /* cp now points to the comment part. */ |
| |
| /* Check if the we have found the desired key (identified by its modulus). */ |
| if (BN_cmp(pk->n, client_n) != 0) |
| continue; |
| |
| /* check the real bits */ |
| if (bits != BN_num_bits(pk->n)) |
| log("Warning: %s, line %ld: keysize mismatch: " |
| "actual %d vs. announced %d.", |
| file, linenum, BN_num_bits(pk->n), bits); |
| |
| /* We have found the desired key. */ |
| |
| |
| /* Perform the challenge-response dialog for this key. */ |
| if (!auth_rsa_challenge_dialog(pk)) { |
| /* Wrong response. */ |
| verbose("Wrong response to RSA authentication challenge."); |
| packet_send_debug("Wrong response to RSA authentication challenge."); |
| continue; |
| } |
| /* |
| * 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; |
| } |
| 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; |
| } |
| 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); |
| /* key invalid for this host, reset flags */ |
| authenticated = 0; |
| no_agent_forwarding_flag = 0; |
| no_port_forwarding_flag = 0; |
| no_pty_flag = 0; |
| no_x11_forwarding_flag = 0; |
| while (custom_environment) { |
| struct envstring *ce = custom_environment; |
| custom_environment = ce->next; |
| xfree(ce->s); |
| xfree(ce); |
| } |
| if (forced_command) { |
| xfree(forced_command); |
| forced_command = NULL; |
| } |
| break; |
| } |
| xfree(patterns); |
| /* Host name matches. */ |
| goto next_option; |
| } |
| bad_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; |
| } |
| } |
| /* |
| * Break out of the loop if authentication was successful; |
| * otherwise continue searching. |
| */ |
| if (authenticated) |
| break; |
| } |
| |
| /* Restore the privileged uid. */ |
| restore_uid(); |
| |
| /* Close the file. */ |
| fclose(f); |
| |
| RSA_free(pk); |
| |
| if (authenticated) |
| packet_send_debug("RSA authentication accepted."); |
| |
| /* Return authentication result. */ |
| return authenticated; |
| } |