authenticate.c

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/* -*- c-file-style: "linux"; -*-

   Copyright (C) 1998-2000 by Andrew Tridgell

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/* support rsync authentication */
#include "rsync.h"

extern char *password_file;

/***************************************************************************
encode a buffer using base64 - simple and slow algorithm. null terminates
the result.
  ***************************************************************************/
void base64_encode(char *buf, int len, char *out, int pad)
{
        char *b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
        int bit_offset, byte_offset, idx, i;
        unsigned char *d = (unsigned char *)buf;
        int bytes = (len*8 + 5)/6;

        for (i = 0; i < bytes; i++) {
                byte_offset = (i*6)/8;
                bit_offset = (i*6)%8;
                if (bit_offset < 3) {
                        idx = (d[byte_offset] >> (2-bit_offset)) & 0x3F;
                } else {
                        idx = (d[byte_offset] << (bit_offset-2)) & 0x3F;
                        if (byte_offset+1 < len) {
                                idx |= (d[byte_offset+1] >> (8-(bit_offset-2)));
                        }
                }
                out[i] = b64[idx];
        }

        while (pad && (i % 4))
                out[i++] = '=';

        out[i] = '\0';
}

/* Generate a challenge buffer and return it base64-encoded. */
static void gen_challenge(char *addr, char *challenge)
{
        char input[32];
        char md4_out[MD4_SUM_LENGTH];
        struct timeval tv;

        memset(input, 0, sizeof input);

        strlcpy((char *)input, addr, 17);
        sys_gettimeofday(&tv);
        SIVAL(input, 16, tv.tv_sec);
        SIVAL(input, 20, tv.tv_usec);
        SIVAL(input, 24, getpid());

        sum_init(0);
        sum_update(input, sizeof input);
        sum_end(md4_out);

        base64_encode(md4_out, MD4_SUM_LENGTH, challenge, 0);
}


/* Return the secret for a user from the secret file, null terminated.
 * Maximum length is len (not counting the null). */
static int get_secret(int module, char *user, char *secret, int len)
{
        char *fname = lp_secrets_file(module);
        STRUCT_STAT st;
        int fd, ok = 1;
        char ch, *p;

        if (!fname || !*fname)
                return 0;

        if ((fd = open(fname, O_RDONLY)) < 0)
                return 0;

        if (do_stat(fname, &st) == -1) {
                rsyserr(FLOG, errno, "stat(%s)", fname);
                ok = 0;
        } else if (lp_strict_modes(module)) {
                if ((st.st_mode & 06) != 0) {
                        rprintf(FLOG, "secrets file must not be other-accessible (see strict modes option)\n");
                        ok = 0;
                } else if (MY_UID() == 0 && st.st_uid != 0) {
                        rprintf(FLOG, "secrets file must be owned by root when running as root (see strict modes)\n");
                        ok = 0;
                }
        }
        if (!ok) {
                rprintf(FLOG, "continuing without secrets file\n");
                close(fd);
                return 0;
        }

        if (*user == '#') {
                /* Reject attempt to match a comment. */
                close(fd);
                return 0;
        }

        /* Try to find a line that starts with the user name and a ':'. */
        p = user;
        while (1) {
                if (read(fd, &ch, 1) != 1) {
                        close(fd);
                        return 0;
                }
                if (ch == '\n')
                        p = user;
                else if (p) {
                        if (*p == ch)
                                p++;
                        else if (!*p && ch == ':')
                                break;
                        else
                                p = NULL;
                }
        }

        /* Slurp the secret into the "secret" buffer. */
        p = secret;
        while (len > 0) {
                if (read(fd, p, 1) != 1 || *p == '\n')
                        break;
                if (*p == '\r')
                        continue;
                p++;
                len--;
        }
        *p = '\0';
        close(fd);

        return 1;
}

static char *getpassf(char *filename)
{
        STRUCT_STAT st;
        char buffer[512], *p;
        int fd, n, ok = 1;
        char *envpw = getenv("RSYNC_PASSWORD");

        if (!filename)
                return NULL;

        if ((fd = open(filename,O_RDONLY)) < 0) {
                rsyserr(FERROR, errno, "could not open password file \"%s\"",
                        filename);
                if (envpw)
                        rprintf(FERROR, "falling back to RSYNC_PASSWORD environment variable.\n");
                return NULL;
        }

        if (do_stat(filename, &st) == -1) {
                rsyserr(FERROR, errno, "stat(%s)", filename);
                ok = 0;
        } else if ((st.st_mode & 06) != 0) {
                rprintf(FERROR,"password file must not be other-accessible\n");
                ok = 0;
        } else if (MY_UID() == 0 && st.st_uid != 0) {
                rprintf(FERROR,"password file must be owned by root when running as root\n");
                ok = 0;
        }
        if (!ok) {
                rprintf(FERROR,"continuing without password file\n");
                if (envpw)
                        rprintf(FERROR, "using RSYNC_PASSWORD environment variable.\n");
                close(fd);
                return NULL;
        }

        if (envpw)
                rprintf(FERROR, "RSYNC_PASSWORD environment variable ignored\n");

        n = read(fd, buffer, sizeof buffer - 1);
        close(fd);
        if (n > 0) {
                buffer[n] = '\0';
                if ((p = strtok(buffer, "\n\r")) != NULL)
                        return strdup(p);
        }

        return NULL;
}

/* Generate an MD4 hash created from the combination of the password
 * and the challenge string and return it base64-encoded. */
static void generate_hash(char *in, char *challenge, char *out)
{
        char buf[MD4_SUM_LENGTH];

        sum_init(0);
        sum_update(in, strlen(in));
        sum_update(challenge, strlen(challenge));
        sum_end(buf);

        base64_encode(buf, MD4_SUM_LENGTH, out, 0);
}

/* Possibly negotiate authentication with the client.  Use "leader" to
 * start off the auth if necessary.
 *
 * Return NULL if authentication failed.  Return "" if anonymous access.
 * Otherwise return username.
 */
char *auth_server(int f_in, int f_out, int module, char *host, char *addr,
                  char *leader)
{
        char *users = lp_auth_users(module);
        char challenge[MD4_SUM_LENGTH*2];
        char line[BIGPATHBUFLEN];
        char secret[512];
        char pass2[MD4_SUM_LENGTH*2];
        char *tok, *pass;

        /* if no auth list then allow anyone in! */
        if (!users || !*users)
                return "";

        gen_challenge(addr, challenge);

        io_printf(f_out, "%s%s\n", leader, challenge);

        if (!read_line(f_in, line, sizeof line - 1)
         || (pass = strchr(line, ' ')) == NULL) {
                rprintf(FLOG, "auth failed on module %s from %s (%s): "
                        "invalid challenge response\n",
                        lp_name(module), host, addr);
                return NULL;
        }
        *pass++ = '\0';

        if (!(users = strdup(users)))
                out_of_memory("auth_server");

        for (tok = strtok(users, " ,\t"); tok; tok = strtok(NULL, " ,\t")) {
                if (wildmatch(tok, line))
                        break;
        }
        free(users);

        if (!tok) {
                rprintf(FLOG, "auth failed on module %s from %s (%s): "
                        "unauthorized user\n",
                        lp_name(module), host, addr);
                return NULL;
        }

        memset(secret, 0, sizeof secret);
        if (!get_secret(module, line, secret, sizeof secret - 1)) {
                memset(secret, 0, sizeof secret);
                rprintf(FLOG, "auth failed on module %s from %s (%s): "
                        "missing secret for user \"%s\"\n",
                        lp_name(module), host, addr, line);
                return NULL;
        }

        generate_hash(secret, challenge, pass2);
        memset(secret, 0, sizeof secret);

        if (strcmp(pass, pass2) != 0) {
                rprintf(FLOG, "auth failed on module %s from %s (%s): "
                        "password mismatch\n",
                        lp_name(module), host, addr);
                return NULL;
        }

        return strdup(line);
}


void auth_client(int fd, char *user, char *challenge)
{
        char *pass;
        char pass2[MD4_SUM_LENGTH*2];

        if (!user || !*user)
                user = "nobody";

        if (!(pass = getpassf(password_file))
         && !(pass = getenv("RSYNC_PASSWORD"))) {
                /* XXX: cyeoh says that getpass is deprecated, because
                 * it may return a truncated password on some systems,
                 * and it is not in the LSB.
                 *
                 * Andrew Klein says that getpassphrase() is present
                 * on Solaris and reads up to 256 characters.
                 *
                 * OpenBSD has a readpassphrase() that might be more suitable.
                 */
                pass = getpass("Password: ");
        }

        if (!pass)
                pass = "";

        generate_hash(pass, challenge, pass2);
        io_printf(fd, "%s %s\n", user, pass2);
}

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