diff options
author | markm <markm@FreeBSD.org> | 2000-02-24 14:29:47 +0000 |
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committer | markm <markm@FreeBSD.org> | 2000-02-24 14:29:47 +0000 |
commit | fc557ff7d97438559e69347575f5aa8ef03a5f50 (patch) | |
tree | c90ea5392aa03e7619696143bde781f2bf5c0dff /crypto/openssh/auth-rsa.c | |
download | FreeBSD-src-fc557ff7d97438559e69347575f5aa8ef03a5f50.zip FreeBSD-src-fc557ff7d97438559e69347575f5aa8ef03a5f50.tar.gz |
Vendor import of OpenSSH.
Diffstat (limited to 'crypto/openssh/auth-rsa.c')
-rw-r--r-- | crypto/openssh/auth-rsa.c | 477 |
1 files changed, 477 insertions, 0 deletions
diff --git a/crypto/openssh/auth-rsa.c b/crypto/openssh/auth-rsa.c new file mode 100644 index 0000000..a04adf6 --- /dev/null +++ b/crypto/openssh/auth-rsa.c @@ -0,0 +1,477 @@ +/* + * + * 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 2000/02/11 10:59:11 markus Exp $"); + +#include "rsa.h" +#include "packet.h" +#include "xmalloc.h" +#include "ssh.h" +#include "mpaux.h" +#include "uidswap.h" +#include "servconf.h" + +#include <ssl/rsa.h> +#include <ssl/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(BIGNUM *e, BIGNUM *n) +{ + BIGNUM *challenge, *encrypted_challenge; + RSA *pk; + 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, n, ctx); + BN_CTX_free(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(); + 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; + BIGNUM *e, *n; + + /* 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) { + log(buf); + packet_send_debug(buf); + restore_uid(); + return 0; + } + } + /* Flag indicating whether authentication has succeeded. */ + authenticated = 0; + + 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, 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, 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; + } + /* 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; + + /* check the real bits */ + if (bits != BN_num_bits(n)) + log("Warning: %s, line %ld: keysize mismatch: " + "actual %d vs. announced %d.", + file, linenum, BN_num_bits(n), bits); + + /* We have found the desired key. */ + + /* Perform the challenge-response dialog for this key. */ + if (!auth_rsa_challenge_dialog(e, n)) { + /* 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); + + BN_clear_free(n); + BN_clear_free(e); + + if (authenticated) + packet_send_debug("RSA authentication accepted."); + + /* Return authentication result. */ + return authenticated; +} |