+/* $OpenBSD: auth-rsa.c,v 1.73 2008/07/02 12:03:51 dtucker Exp $ */
/*
+ * Author: Tatu Ylonen <ylo@cs.hut.fi>
+ * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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 <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
+#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 <sys/types.h>
+#include <sys/stat.h>
-*/
+#include <openssl/rsa.h>
+#include <openssl/md5.h>
-#include "includes.h"
-RCSID("$Id$");
+#include <pwd.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <string.h>
+#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 <openssl/rsa.h>
-#include <openssl/md5.h>
-#endif
-#ifdef HAVE_SSL
-#include <ssl/rsa.h>
-#include <ssl/md5.h>
+#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);
}
andersk / openssh.git / blobdiff