svcgssd_krb5.c

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/*
 * COPYRIGHT (c) 2011
 * The Regents of the University of Michigan
 * ALL RIGHTS RESERVED
 *
 * Permission is granted to use, copy, create derivative works
 * and redistribute this software and such derivative works
 * for any purpose, so long as the name of The University of
 * Michigan is not used in any advertising or publicity
 * pertaining to the use of distribution of this software
 * without specific, written prior authorization.  If the
 * above copyright notice or any other identification of the
 * University of Michigan is included in any copy of any
 * portion of this software, then the disclaimer below must
 * also be included.
 *
 * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
 * FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY
 * PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF
 * MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING
 * WITHOUT LIMITATION THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
 * REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE
 * FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR
 * CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
 * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGES.
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif  /* HAVE_CONFIG_H */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <stdio.h>
#include <errno.h>
#include <gssapi/gssapi.h>
#include <krb5.h>

#include "gss_util.h"
#include "gss_oids.h"
#include "err_util.h"
#include "svcgssd_krb5.h"
#include "../mount/version.h"

#define MYBUFLEN 1024

char *supported_enctypes_filename = "/proc/fs/nfsd/supported_krb5_enctypes";
int parsed_num_enctypes = 0;
krb5_enctype *parsed_enctypes = NULL;
char *cached_enctypes = NULL;

/*==========================*/
/*===  Internal routines ===*/
/*==========================*/

/*
 * Parse the supported encryption type information
 */
static int
parse_enctypes(char *enctypes)
{
        int n = 0;
        char *curr, *comma;
        int i;

        /* Don't parse the same string over and over... */
        if (cached_enctypes && strcmp(cached_enctypes, enctypes) == 0)
                return 0;

        /* Free any existing cached_enctypes */
        free(cached_enctypes);

        if (parsed_enctypes != NULL) {
                free(parsed_enctypes);
                parsed_enctypes = NULL;
                parsed_num_enctypes = 0;
        }

        /* count the number of commas */
        for (curr = enctypes; curr && *curr != '\0'; curr = ++comma) {
                comma = strchr(curr, ',');
                if (comma != NULL)
                        n++;
                else
                        break;
        }

        /* If no more commas and we're not at the end, there's one more value */
        if (*curr != '\0')
                n++;

        /* Empty string, return an error */
        if (n == 0)
                return ENOENT;

        /* Allocate space for enctypes array */
        if ((parsed_enctypes = (int *) calloc(n, sizeof(int))) == NULL) {
                return ENOMEM;
        }

        /* Now parse each value into the array */
        for (curr = enctypes, i = 0; curr && *curr != '\0'; curr = ++comma) {
                parsed_enctypes[i++] = atoi(curr);
                comma = strchr(curr, ',');
                if (comma == NULL)
                        break;
        }

        parsed_num_enctypes = n;
        if ((cached_enctypes = malloc(strlen(enctypes)+1)))
                strcpy(cached_enctypes, enctypes);

        return 0;
}

static void
get_kernel_supported_enctypes(void)
{
        FILE *s_e;
        int ret;
        char buffer[MYBUFLEN + 1];

        memset(buffer, '\0', sizeof(buffer));

        s_e = fopen(supported_enctypes_filename, "r");
        if (s_e == NULL)
                goto out_clean_parsed;

        ret = fread(buffer, 1, MYBUFLEN, s_e);
        if (ret < 0) {
                fclose(s_e);
                goto out_clean_parsed;
        }
        fclose(s_e);
        if (parse_enctypes(buffer)) {
                goto out_clean_parsed;
        }
out:
        return;

out_clean_parsed:
        if (parsed_enctypes != NULL) {
                free(parsed_enctypes);
                parsed_num_enctypes = 0;
        }
        goto out;
}

/*==========================*/
/*===  External routines ===*/
/*==========================*/

/*
 * Get encryption types supported by the kernel, and then
 * call gss_krb5_set_allowable_enctypes() to limit the
 * encryption types negotiated.
 *
 * Returns:
 *      0 => all went well
 *     -1 => there was an error
 */

int
svcgssd_limit_krb5_enctypes(void)
{
#ifdef HAVE_SET_ALLOWABLE_ENCTYPES
        u_int maj_stat, min_stat;
        krb5_enctype old_kernel_enctypes[] = {
                ENCTYPE_DES_CBC_CRC,
                ENCTYPE_DES_CBC_MD5,
                ENCTYPE_DES_CBC_MD4 };
        krb5_enctype new_kernel_enctypes[] = {
                ENCTYPE_AES256_CTS_HMAC_SHA1_96,
                ENCTYPE_AES128_CTS_HMAC_SHA1_96,
                ENCTYPE_DES3_CBC_SHA1,
                ENCTYPE_ARCFOUR_HMAC,
                ENCTYPE_DES_CBC_CRC,
                ENCTYPE_DES_CBC_MD5,
                ENCTYPE_DES_CBC_MD4 };
        krb5_enctype *default_enctypes, *enctypes;
        int default_num_enctypes, num_enctypes;


        if (linux_version_code() < MAKE_VERSION(2, 6, 35)) {
                default_enctypes = old_kernel_enctypes;
                default_num_enctypes =
                        sizeof(old_kernel_enctypes) / sizeof(old_kernel_enctypes[0]);
        } else {
                default_enctypes = new_kernel_enctypes;
                default_num_enctypes =
                        sizeof(new_kernel_enctypes) / sizeof(new_kernel_enctypes[0]);
        }

        get_kernel_supported_enctypes();

        if (parsed_enctypes != NULL) {
                enctypes = parsed_enctypes;
                num_enctypes = parsed_num_enctypes;
                printerr(2, "%s: Calling gss_set_allowable_enctypes with %d "
                        "enctypes from the kernel\n", __func__, num_enctypes);
        } else {
                enctypes = default_enctypes;
                num_enctypes = default_num_enctypes;
                printerr(2, "%s: Calling gss_set_allowable_enctypes with %d "
                        "enctypes from defaults\n", __func__, num_enctypes);
        }

        maj_stat = gss_set_allowable_enctypes(&min_stat, gssd_creds,
                        &krb5oid, num_enctypes, enctypes);
        if (maj_stat != GSS_S_COMPLETE) {
                printerr(1, "WARNING: gss_set_allowable_enctypes failed\n");
                pgsserr("svcgssd_limit_krb5_enctypes: gss_set_allowable_enctypes",
                        maj_stat, min_stat, &krb5oid);
                return -1;
        }
#endif
        return 0;
}