/* $OpenBSD: auth2.c,v 1.170 2025/01/17 00:09:41 dtucker Exp $ */
/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/uio.h>

#include <fcntl.h>
#include <limits.h>
#include <pwd.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <time.h>

#include "stdlib.h"
#include "atomicio.h"
#include "xmalloc.h"
#include "ssh2.h"
#include "packet.h"
#include "log.h"
#include "sshbuf.h"
#include "misc.h"
#include "servconf.h"
#include "sshkey.h"
#include "hostfile.h"
#include "auth.h"
#include "dispatch.h"
#include "pathnames.h"
#include "ssherr.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"
#include "digest.h"
#include "kex.h"

/* import */
extern ServerOptions options;
extern struct sshbuf *loginmsg;

/* methods */

extern Authmethod method_none;
extern Authmethod method_pubkey;
extern Authmethod method_passwd;
extern Authmethod method_kbdint;
extern Authmethod method_hostbased;
#ifdef GSSAPI
extern Authmethod method_gssapi;
#endif

Authmethod *authmethods[] = {
        &method_none,
        &method_pubkey,
#ifdef GSSAPI
        &method_gssapi,
#endif
        &method_passwd,
        &method_kbdint,
        &method_hostbased,
        NULL
};

/* protocol */

static int input_service_request(int, u_int32_t, struct ssh *);
static int input_userauth_request(int, u_int32_t, struct ssh *);

/* helper */
static Authmethod *authmethod_byname(const char *);
static Authmethod *authmethod_lookup(Authctxt *, const char *);
static char *authmethods_get(Authctxt *authctxt);

#define MATCH_NONE      0       /* method or submethod mismatch */
#define MATCH_METHOD    1       /* method matches (no submethod specified) */
#define MATCH_BOTH      2       /* method and submethod match */
#define MATCH_PARTIAL   3       /* method matches, submethod can't be checked */
static int list_starts_with(const char *, const char *, const char *);

char *
auth2_read_banner(void)
{
        struct stat st;
        char *banner = NULL;
        size_t len, n;
        int fd;

        if ((fd = open(options.banner, O_RDONLY)) == -1)
                return (NULL);
        if (fstat(fd, &st) == -1) {
                close(fd);
                return (NULL);
        }
        if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
                close(fd);
                return (NULL);
        }

        len = (size_t)st.st_size;               /* truncate */
        banner = xmalloc(len + 1);
        n = atomicio(read, fd, banner, len);
        close(fd);

        if (n != len) {
                free(banner);
                return (NULL);
        }
        banner[n] = '\0';

        return (banner);
}

static void
userauth_send_banner(struct ssh *ssh, const char *msg)
{
        int r;

        if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_BANNER)) != 0 ||
            (r = sshpkt_put_cstring(ssh, msg)) != 0 ||
            (r = sshpkt_put_cstring(ssh, "")) != 0 ||   /* language, unused */
            (r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "send packet");
        debug("%s: sent", __func__);
}

static void
userauth_banner(struct ssh *ssh)
{
        char *banner = NULL;

        if (options.banner == NULL)
                return;

        if ((banner = mm_auth2_read_banner()) == NULL)
                goto done;
        userauth_send_banner(ssh, banner);

done:
        free(banner);
}

/*
 * loop until authctxt->success == TRUE
 */
void
do_authentication2(struct ssh *ssh)
{
        Authctxt *authctxt = ssh->authctxt;

        ssh_dispatch_init(ssh, &dispatch_protocol_error);
        if (ssh->kex->ext_info_c)
                ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_input_ext_info);
        ssh_dispatch_set(ssh, SSH2_MSG_SERVICE_REQUEST, &input_service_request);
        ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &authctxt->success);
        ssh->authctxt = NULL;
}

static int
input_service_request(int type, u_int32_t seq, struct ssh *ssh)
{
        Authctxt *authctxt = ssh->authctxt;
        char *service = NULL;
        int r, acceptit = 0;

        if ((r = sshpkt_get_cstring(ssh, &service, NULL)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0)
                goto out;

        if (authctxt == NULL)
                fatal("input_service_request: no authctxt");

        if (strcmp(service, "ssh-userauth") == 0) {
                if (!authctxt->success) {
                        acceptit = 1;
                        /* now we can handle user-auth requests */
                        ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST,
                            &input_userauth_request);
                }
        }
        /* XXX all other service requests are denied */

        if (acceptit) {
                if ((r = sshpkt_start(ssh, SSH2_MSG_SERVICE_ACCEPT)) != 0 ||
                    (r = sshpkt_put_cstring(ssh, service)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0 ||
                    (r = ssh_packet_write_wait(ssh)) != 0)
                        goto out;
        } else {
                debug("bad service request %s", service);
                ssh_packet_disconnect(ssh, "bad service request %s", service);
        }
        ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &dispatch_protocol_error);
        r = 0;
 out:
        free(service);
        return r;
}

#define MIN_FAIL_DELAY_SECONDS 0.005
#define MAX_FAIL_DELAY_SECONDS 5.0
static double
user_specific_delay(const char *user)
{
        char b[512];
        size_t len = ssh_digest_bytes(SSH_DIGEST_SHA512);
        u_char *hash = xmalloc(len);
        double delay;

        (void)snprintf(b, sizeof b, "%llu%s",
            (unsigned long long)options.timing_secret, user);
        if (ssh_digest_memory(SSH_DIGEST_SHA512, b, strlen(b), hash, len) != 0)
                fatal_f("ssh_digest_memory");
        /* 0-4.2 ms of delay */
        delay = (double)PEEK_U32(hash) / 1000 / 1000 / 1000 / 1000;
        freezero(hash, len);
        debug3_f("user specific delay %0.3lfms", delay*1000);
        return MIN_FAIL_DELAY_SECONDS + delay;
}

static void
ensure_minimum_time_since(double start, double seconds)
{
        struct timespec ts;
        double elapsed = monotime_double() - start, req = seconds, remain;

        if (elapsed > MAX_FAIL_DELAY_SECONDS) {
                debug3_f("elapsed %0.3lfms exceeded the max delay "
                    "requested %0.3lfms)", elapsed*1000, req*1000);
                return;
        }

        /* if we've already passed the requested time, scale up */
        while ((remain = seconds - elapsed) < 0.0)
                seconds *= 2;

        ts.tv_sec = remain;
        ts.tv_nsec = (remain - ts.tv_sec) * 1000000000;
        debug3_f("elapsed %0.3lfms, delaying %0.3lfms (requested %0.3lfms)",
            elapsed*1000, remain*1000, req*1000);
        nanosleep(&ts, NULL);
}

static int
input_userauth_request(int type, u_int32_t seq, struct ssh *ssh)
{
        Authctxt *authctxt = ssh->authctxt;
        Authmethod *m = NULL;
        char *user = NULL, *service = NULL, *method = NULL, *style = NULL;
        int r, authenticated = 0;
        double tstart = monotime_double();

        if (authctxt == NULL)
                fatal("input_userauth_request: no authctxt");

        if ((r = sshpkt_get_cstring(ssh, &user, NULL)) != 0 ||
            (r = sshpkt_get_cstring(ssh, &service, NULL)) != 0 ||
            (r = sshpkt_get_cstring(ssh, &method, NULL)) != 0)
                goto out;
        debug("userauth-request for user %s service %s method %s", user, service, method);
        debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);

        if ((style = strchr(user, ':')) != NULL)
                *style++ = 0;

        if (authctxt->attempt >= 1024)
                auth_maxtries_exceeded(ssh);
        if (authctxt->attempt++ == 0) {
                /* setup auth context */
                authctxt->pw = mm_getpwnamallow(ssh, user);
                authctxt->user = xstrdup(user);
                if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
                        authctxt->valid = 1;
                        debug2_f("setting up authctxt for %s", user);
                } else {
                        authctxt->valid = 0;
                        /* Invalid user, fake password information */
                        authctxt->pw = fakepw();
#ifdef SSH_AUDIT_EVENTS
                        mm_audit_event(ssh, SSH_INVALID_USER);
#endif
                }
#ifdef USE_PAM
                if (options.use_pam)
                        mm_start_pam(ssh);
#endif
                ssh_packet_set_log_preamble(ssh, "%suser %s",
                    authctxt->valid ? "authenticating " : "invalid ", user);
                setproctitle("%s [net]", authctxt->valid ? user : "unknown");
                authctxt->service = xstrdup(service);
                authctxt->style = style ? xstrdup(style) : NULL;
                mm_inform_authserv(service, style);
                userauth_banner(ssh);
                if ((r = kex_server_update_ext_info(ssh)) != 0)
                        fatal_fr(r, "kex_server_update_ext_info failed");
                if (auth2_setup_methods_lists(authctxt) != 0)
                        ssh_packet_disconnect(ssh,
                            "no authentication methods enabled");
        } else if (strcmp(user, authctxt->user) != 0 ||
            strcmp(service, authctxt->service) != 0) {
                ssh_packet_disconnect(ssh, "Change of username or service "
                    "not allowed: (%s,%s) -> (%s,%s)",
                    authctxt->user, authctxt->service, user, service);
        }
        /* reset state */
        auth2_challenge_stop(ssh);

#ifdef GSSAPI
        /* XXX move to auth2_gssapi_stop() */
        ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
        ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
#endif

        auth2_authctxt_reset_info(authctxt);
        authctxt->postponed = 0;
        authctxt->server_caused_failure = 0;

        /* try to authenticate user */
        m = authmethod_lookup(authctxt, method);
        if (m != NULL && authctxt->failures < options.max_authtries) {
                debug2("input_userauth_request: try method %s", method);
                authenticated = m->userauth(ssh, method);
        }
        if (!authctxt->authenticated && strcmp(method, "none") != 0)
                ensure_minimum_time_since(tstart,
                    user_specific_delay(authctxt->user));
        userauth_finish(ssh, authenticated, method, NULL);
        r = 0;
 out:
        free(service);
        free(user);
        free(method);
        return r;
}

void
userauth_finish(struct ssh *ssh, int authenticated, const char *packet_method,
    const char *submethod)
{
        Authctxt *authctxt = ssh->authctxt;
        Authmethod *m = NULL;
        const char *method = packet_method;
        char *methods;
        int r, partial = 0;

        if (authenticated) {
                if (!authctxt->valid) {
                        fatal("INTERNAL ERROR: authenticated invalid user %s",
                            authctxt->user);
                }
                if (authctxt->postponed)
                        fatal("INTERNAL ERROR: authenticated and postponed");
                /* prefer primary authmethod name to possible synonym */
                if ((m = authmethod_byname(method)) == NULL)
                        fatal("INTERNAL ERROR: bad method %s", method);
                method = m->cfg->name;
        }

        /* Special handling for root */
        if (authenticated && authctxt->pw->pw_uid == 0 &&
            !auth_root_allowed(ssh, method)) {
                authenticated = 0;
#ifdef SSH_AUDIT_EVENTS
                mm_audit_event(ssh, SSH_LOGIN_ROOT_DENIED);
#endif
        }

        if (authenticated && options.num_auth_methods != 0) {
                if (!auth2_update_methods_lists(authctxt, method, submethod)) {
                        authenticated = 0;
                        partial = 1;
                }
        }

        /* Log before sending the reply */
        auth_log(ssh, authenticated, partial, method, submethod);

        /* Update information exposed to session */
        if (authenticated || partial)
                auth2_update_session_info(authctxt, method, submethod);

        if (authctxt->postponed)
                return;

#ifdef USE_PAM
        if (options.use_pam && authenticated) {
                int r, success = mm_do_pam_account();

                /* If PAM returned a message, send it to the user. */
                if (sshbuf_len(loginmsg) > 0) {
                        if ((r = sshbuf_put(loginmsg, "\0", 1)) != 0)
                                fatal("%s: buffer error: %s",
                                    __func__, ssh_err(r));
                        userauth_send_banner(ssh, sshbuf_ptr(loginmsg));
                        if ((r = ssh_packet_write_wait(ssh)) != 0) {
                                sshpkt_fatal(ssh, r,
                                    "%s: send PAM banner", __func__);
                        }
                }
                if (!success) {
                        fatal("Access denied for user %s by PAM account "
                            "configuration", authctxt->user);
                }
        }
#endif

        if (authenticated == 1) {
                /* turn off userauth */
                ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST,
                    &dispatch_protocol_ignore);
                if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_SUCCESS)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0 ||
                    (r = ssh_packet_write_wait(ssh)) != 0)
                        fatal_fr(r, "send success packet");
                /* now we can break out */
                authctxt->success = 1;
                ssh_packet_set_log_preamble(ssh, "user %s", authctxt->user);
        } else {
                /* Allow initial try of "none" auth without failure penalty */
                if (!partial && !authctxt->server_caused_failure &&
                    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
                        authctxt->failures++;
                if (authctxt->failures >= options.max_authtries) {
#ifdef SSH_AUDIT_EVENTS
                        mm_audit_event(ssh, SSH_LOGIN_EXCEED_MAXTRIES);
#endif
                        auth_maxtries_exceeded(ssh);
                }
                methods = authmethods_get(authctxt);
                debug3_f("failure partial=%d next methods=\"%s\"",
                    partial, methods);
                if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_FAILURE)) != 0 ||
                    (r = sshpkt_put_cstring(ssh, methods)) != 0 ||
                    (r = sshpkt_put_u8(ssh, partial)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0 ||
                    (r = ssh_packet_write_wait(ssh)) != 0)
                        fatal_fr(r, "send failure packet");
                free(methods);
        }
}

/*
 * Checks whether method is allowed by at least one AuthenticationMethods
 * methods list. Returns 1 if allowed, or no methods lists configured.
 * 0 otherwise.
 */
int
auth2_method_allowed(Authctxt *authctxt, const char *method,
    const char *submethod)
{
        u_int i;

        /*
         * NB. authctxt->num_auth_methods might be zero as a result of
         * auth2_setup_methods_lists(), so check the configuration.
         */
        if (options.num_auth_methods == 0)
                return 1;
        for (i = 0; i < authctxt->num_auth_methods; i++) {
                if (list_starts_with(authctxt->auth_methods[i], method,
                    submethod) != MATCH_NONE)
                        return 1;
        }
        return 0;
}

static char *
authmethods_get(Authctxt *authctxt)
{
        struct sshbuf *b;
        char *list;
        int i, r;

        if ((b = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        for (i = 0; authmethods[i] != NULL; i++) {
                if (strcmp(authmethods[i]->cfg->name, "none") == 0)
                        continue;
                if (authmethods[i]->cfg->enabled == NULL ||
                    *(authmethods[i]->cfg->enabled) == 0)
                        continue;
                if (!auth2_method_allowed(authctxt, authmethods[i]->cfg->name,
                    NULL))
                        continue;
                if ((r = sshbuf_putf(b, "%s%s", sshbuf_len(b) ? "," : "",
                    authmethods[i]->cfg->name)) != 0)
                        fatal_fr(r, "buffer error");
        }
        if ((list = sshbuf_dup_string(b)) == NULL)
                fatal_f("sshbuf_dup_string failed");
        sshbuf_free(b);
        return list;
}

static Authmethod *
authmethod_byname(const char *name)
{
        int i;

        if (name == NULL)
                fatal_f("NULL authentication method name");
        for (i = 0; authmethods[i] != NULL; i++) {
                if (strcmp(name, authmethods[i]->cfg->name) == 0 ||
                    (authmethods[i]->cfg->synonym != NULL &&
                    strcmp(name, authmethods[i]->cfg->synonym) == 0))
                        return authmethods[i];
        }
        debug_f("unrecognized authentication method name: %s", name);
        return NULL;
}

static Authmethod *
authmethod_lookup(Authctxt *authctxt, const char *name)
{
        Authmethod *method;

        if ((method = authmethod_byname(name)) == NULL)
                return NULL;

        if (method->cfg->enabled == NULL || *(method->cfg->enabled) == 0) {
                debug3_f("method %s not enabled", name);
                return NULL;
        }
        if (!auth2_method_allowed(authctxt, method->cfg->name, NULL)) {
                debug3_f("method %s not allowed "
                    "by AuthenticationMethods", name);
                return NULL;
        }
        return method;
}

/*
 * Prune the AuthenticationMethods supplied in the configuration, removing
 * any methods lists that include disabled methods. Note that this might
 * leave authctxt->num_auth_methods == 0, even when multiple required auth
 * has been requested. For this reason, all tests for whether multiple is
 * enabled should consult options.num_auth_methods directly.
 */
int
auth2_setup_methods_lists(Authctxt *authctxt)
{
        u_int i;

        /* First, normalise away the "any" pseudo-method */
        if (options.num_auth_methods == 1 &&
            strcmp(options.auth_methods[0], "any") == 0) {
                free(options.auth_methods[0]);
                options.auth_methods[0] = NULL;
                options.num_auth_methods = 0;
        }

        if (options.num_auth_methods == 0)
                return 0;
        debug3_f("checking methods");
        authctxt->auth_methods = xcalloc(options.num_auth_methods,
            sizeof(*authctxt->auth_methods));
        authctxt->num_auth_methods = 0;
        for (i = 0; i < options.num_auth_methods; i++) {
                if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
                        logit("Authentication methods list \"%s\" contains "
                            "disabled method, skipping",
                            options.auth_methods[i]);
                        continue;
                }
                debug("authentication methods list %d: %s",
                    authctxt->num_auth_methods, options.auth_methods[i]);
                authctxt->auth_methods[authctxt->num_auth_methods++] =
                    xstrdup(options.auth_methods[i]);
        }
        if (authctxt->num_auth_methods == 0) {
                error("No AuthenticationMethods left after eliminating "
                    "disabled methods");
                return -1;
        }
        return 0;
}

static int
list_starts_with(const char *methods, const char *method,
    const char *submethod)
{
        size_t l = strlen(method);
        int match;
        const char *p;

        if (strncmp(methods, method, l) != 0)
                return MATCH_NONE;
        p = methods + l;
        match = MATCH_METHOD;
        if (*p == ':') {
                if (!submethod)
                        return MATCH_PARTIAL;
                l = strlen(submethod);
                p += 1;
                if (strncmp(submethod, p, l))
                        return MATCH_NONE;
                p += l;
                match = MATCH_BOTH;
        }
        if (*p != ',' && *p != '\0')
                return MATCH_NONE;
        return match;
}

/*
 * Remove method from the start of a comma-separated list of methods.
 * Returns 0 if the list of methods did not start with that method or 1
 * if it did.
 */
static int
remove_method(char **methods, const char *method, const char *submethod)
{
        char *omethods = *methods, *p;
        size_t l = strlen(method);
        int match;

        match = list_starts_with(omethods, method, submethod);
        if (match != MATCH_METHOD && match != MATCH_BOTH)
                return 0;
        p = omethods + l;
        if (submethod && match == MATCH_BOTH)
                p += 1 + strlen(submethod); /* include colon */
        if (*p == ',')
                p++;
        *methods = xstrdup(p);
        free(omethods);
        return 1;
}

/*
 * Called after successful authentication. Will remove the successful method
 * from the start of each list in which it occurs. If it was the last method
 * in any list, then authentication is deemed successful.
 * Returns 1 if the method completed any authentication list or 0 otherwise.
 */
int
auth2_update_methods_lists(Authctxt *authctxt, const char *method,
    const char *submethod)
{
        u_int i, found = 0;

        debug3_f("updating methods list after \"%s\"", method);
        for (i = 0; i < authctxt->num_auth_methods; i++) {
                if (!remove_method(&(authctxt->auth_methods[i]), method,
                    submethod))
                        continue;
                found = 1;
                if (*authctxt->auth_methods[i] == '\0') {
                        debug2("authentication methods list %d complete", i);
                        return 1;
                }
                debug3("authentication methods list %d remaining: \"%s\"",
                    i, authctxt->auth_methods[i]);
        }
        /* This should not happen, but would be bad if it did */
        if (!found)
                fatal_f("method not in AuthenticationMethods");
        return 0;
}

/* Reset method-specific information */
void auth2_authctxt_reset_info(Authctxt *authctxt)
{
        sshkey_free(authctxt->auth_method_key);
        free(authctxt->auth_method_info);
        authctxt->auth_method_key = NULL;
        authctxt->auth_method_info = NULL;
}

/* Record auth method-specific information for logs */
void
auth2_record_info(Authctxt *authctxt, const char *fmt, ...)
{
        va_list ap;
        int i;

        free(authctxt->auth_method_info);
        authctxt->auth_method_info = NULL;

        va_start(ap, fmt);
        i = vasprintf(&authctxt->auth_method_info, fmt, ap);
        va_end(ap);

        if (i == -1)
                fatal_f("vasprintf failed");
}

/*
 * Records a public key used in authentication. This is used for logging
 * and to ensure that the same key is not subsequently accepted again for
 * multiple authentication.
 */
void
auth2_record_key(Authctxt *authctxt, int authenticated,
    const struct sshkey *key)
{
        struct sshkey **tmp, *dup;
        int r;

        if ((r = sshkey_from_private(key, &dup)) != 0)
                fatal_fr(r, "copy key");
        sshkey_free(authctxt->auth_method_key);
        authctxt->auth_method_key = dup;

        if (!authenticated)
                return;

        /* If authenticated, make sure we don't accept this key again */
        if ((r = sshkey_from_private(key, &dup)) != 0)
                fatal_fr(r, "copy key");
        if (authctxt->nprev_keys >= INT_MAX ||
            (tmp = recallocarray(authctxt->prev_keys, authctxt->nprev_keys,
            authctxt->nprev_keys + 1, sizeof(*authctxt->prev_keys))) == NULL)
                fatal_f("reallocarray failed");
        authctxt->prev_keys = tmp;
        authctxt->prev_keys[authctxt->nprev_keys] = dup;
        authctxt->nprev_keys++;

}

/* Checks whether a key has already been previously used for authentication */
int
auth2_key_already_used(Authctxt *authctxt, const struct sshkey *key)
{
        u_int i;
        char *fp;

        for (i = 0; i < authctxt->nprev_keys; i++) {
                if (sshkey_equal_public(key, authctxt->prev_keys[i])) {
                        fp = sshkey_fingerprint(authctxt->prev_keys[i],
                            options.fingerprint_hash, SSH_FP_DEFAULT);
                        debug3_f("key already used: %s %s",
                            sshkey_type(authctxt->prev_keys[i]),
                            fp == NULL ? "UNKNOWN" : fp);
                        free(fp);
                        return 1;
                }
        }
        return 0;
}

/*
 * Updates authctxt->session_info with details of authentication. Should be
 * whenever an authentication method succeeds.
 */
void
auth2_update_session_info(Authctxt *authctxt, const char *method,
    const char *submethod)
{
        int r;

        if (authctxt->session_info == NULL) {
                if ((authctxt->session_info = sshbuf_new()) == NULL)
                        fatal_f("sshbuf_new");
        }

        /* Append method[/submethod] */
        if ((r = sshbuf_putf(authctxt->session_info, "%s%s%s",
            method, submethod == NULL ? "" : "/",
            submethod == NULL ? "" : submethod)) != 0)
                fatal_fr(r, "append method");

        /* Append key if present */
        if (authctxt->auth_method_key != NULL) {
                if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
                    (r = sshkey_format_text(authctxt->auth_method_key,
                    authctxt->session_info)) != 0)
                        fatal_fr(r, "append key");
        }

        if (authctxt->auth_method_info != NULL) {
                /* Ensure no ambiguity here */
                if (strchr(authctxt->auth_method_info, '\n') != NULL)
                        fatal_f("auth_method_info contains \\n");
                if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
                    (r = sshbuf_putf(authctxt->session_info, "%s",
                    authctxt->auth_method_info)) != 0) {
                        fatal_fr(r, "append method info");
                }
        }
        if ((r = sshbuf_put_u8(authctxt->session_info, '\n')) != 0)
                fatal_fr(r, "append");
}