lib/dns/gssapictx.c

	gssapictx.c revision 0c27b3fe77ac1d5094ba3521e8142d9e7973133f
/*
 * Copyright (C) 2000, 2001, 2004-2016  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/* $Id: gssapictx.c,v 1.29 2011/08/29 06:33:25 marka Exp $ */

#include <config.h>

#include <ctype.h>
#include <stdlib.h>
#include <string.h>

#include <isc/buffer.h>
#include <isc/dir.h>
#include <isc/entropy.h>
#include <isc/file.h>
#include <isc/lex.h>
#include <isc/mem.h>
#include <isc/once.h>
#include <isc/print.h>
#include <isc/platform.h>
#include <isc/random.h>
#include <isc/string.h>
#include <isc/time.h>
#include <isc/util.h>

#include <dns/fixedname.h>
#include <dns/name.h>
#include <dns/rdata.h>
#include <dns/rdataclass.h>
#include <dns/result.h>
#include <dns/types.h>
#include <dns/keyvalues.h>
#include <dns/log.h>

#include <dst/gssapi.h>
#include <dst/result.h>

#include "dst_internal.h"

/*
 * If we're using our own SPNEGO implementation (see configure.in),
 * pull it in now.  Otherwise, we just use whatever GSSAPI supplies.
 */
#if defined(GSSAPI) && defined(USE_ISC_SPNEGO)
#include "spnego.h"
#define gss_accept_sec_context  gss_accept_sec_context_spnego
#define gss_init_sec_context    gss_init_sec_context_spnego
#endif

/*
 * Solaris8 apparently needs an explicit OID set, and Solaris10 needs
 * one for anything but Kerberos.  Supplying an explicit OID set
 * doesn't appear to hurt anything in other implementations, so we
 * always use one.  If we're not using our own SPNEGO implementation,
 * we include SPNEGO's OID.
 */
#ifdef GSSAPI
#ifdef WIN32
#include <krb5/krb5.h>
#else
#include ISC_PLATFORM_KRB5HEADER
#endif

static unsigned char krb5_mech_oid_bytes[] = {
    0x2a, 0x86, 0x48, 0x86, 0xf7, 0x12, 0x01, 0x02, 0x02
};

#ifndef USE_ISC_SPNEGO
static unsigned char spnego_mech_oid_bytes[] = {
    0x2b, 0x06, 0x01, 0x05, 0x05, 0x02
};
#endif

static gss_OID_desc mech_oid_set_array[] = {
    { sizeof(krb5_mech_oid_bytes), krb5_mech_oid_bytes },
#ifndef USE_ISC_SPNEGO
    { sizeof(spnego_mech_oid_bytes), spnego_mech_oid_bytes },
#endif
};

static gss_OID_set_desc mech_oid_set = {
    sizeof(mech_oid_set_array) / sizeof(*mech_oid_set_array),
    mech_oid_set_array
};

#endif

#define REGION_TO_GBUFFER(r, gb) \
    do { \
        (gb).length = (r).length; \
        (gb).value = (r).base; \
    } while (0)

#define GBUFFER_TO_REGION(gb, r) \
    do { \
      (r).length = (unsigned int)(gb).length; \
        (r).base = (gb).value; \
    } while (0)


#define RETERR(x) do { \
    result = (x); \
    if (result != ISC_R_SUCCESS) \
        goto out; \
    } while (0)

#ifdef GSSAPI
static inline void
name_to_gbuffer(dns_name_t *name, isc_buffer_t *buffer,
        gss_buffer_desc *gbuffer)
{
    dns_name_t tname, *namep;
    isc_region_t r;
    isc_result_t result;

    if (!dns_name_isabsolute(name))
        namep = name;
    else
    {
        unsigned int labels;
        dns_name_init(&tname, NULL);
        labels = dns_name_countlabels(name);
        dns_name_getlabelsequence(name, 0, labels - 1, &tname);
        namep = &tname;
    }

    result = dns_name_toprincipal(namep, buffer);
    RUNTIME_CHECK(result == ISC_R_SUCCESS);
    isc_buffer_putuint8(buffer, 0);
    isc_buffer_usedregion(buffer, &r);
    REGION_TO_GBUFFER(r, *gbuffer);
}

static void
log_cred(const gss_cred_id_t cred) {
    OM_uint32 gret, minor, lifetime;
    gss_name_t gname;
    gss_buffer_desc gbuffer;
    gss_cred_usage_t usage;
    const char *usage_text;
    char buf[1024];

    gret = gss_inquire_cred(&minor, cred, &gname, &lifetime, &usage, NULL);
    if (gret != GSS_S_COMPLETE) {
        gss_log(3, "failed gss_inquire_cred: %s",
            gss_error_tostring(gret, minor, buf, sizeof(buf)));
        return;
    }

    gret = gss_display_name(&minor, gname, &gbuffer, NULL);
    if (gret != GSS_S_COMPLETE)
        gss_log(3, "failed gss_display_name: %s",
            gss_error_tostring(gret, minor, buf, sizeof(buf)));
    else {
        switch (usage) {
        case GSS_C_BOTH:
            usage_text = "GSS_C_BOTH";
            break;
        case GSS_C_INITIATE:
            usage_text = "GSS_C_INITIATE";
            break;
        case GSS_C_ACCEPT:
            usage_text = "GSS_C_ACCEPT";
            break;
        default:
            usage_text = "???";
        }
        gss_log(3, "gss cred: \"%s\", %s, %lu", (char *)gbuffer.value,
            usage_text, (unsigned long)lifetime);
    }

    if (gret == GSS_S_COMPLETE) {
        if (gbuffer.length != 0U) {
            gret = gss_release_buffer(&minor, &gbuffer);
            if (gret != GSS_S_COMPLETE)
                gss_log(3, "failed gss_release_buffer: %s",
                    gss_error_tostring(gret, minor, buf,
                               sizeof(buf)));
        }
    }

    gret = gss_release_name(&minor, &gname);
    if (gret != GSS_S_COMPLETE)
        gss_log(3, "failed gss_release_name: %s",
            gss_error_tostring(gret, minor, buf, sizeof(buf)));
}
#endif

#ifdef GSSAPI
/*
 * check for the most common configuration errors.
 *
 * The errors checked for are:
 *   - tkey-gssapi-credential doesn't start with DNS/
 *   - the default realm in /etc/krb5.conf and the
 *     tkey-gssapi-credential bind config option don't match
 *
 * Note that if tkey-gssapi-keytab is set then these configure checks
 * are not performed, and runtime errors from gssapi are used instead
 */
static void
check_config(const char *gss_name) {
    const char *p;
    krb5_context krb5_ctx;
    char *krb5_realm_name = NULL;

    if (strncasecmp(gss_name, "DNS/", 4) != 0) {
        gss_log(ISC_LOG_ERROR, "tkey-gssapi-credential (%s) "
            "should start with 'DNS/'", gss_name);
        return;
    }

    if (krb5_init_context(&krb5_ctx) != 0) {
        gss_log(ISC_LOG_ERROR, "Unable to initialise krb5 context");
        return;
    }
    if (krb5_get_default_realm(krb5_ctx, &krb5_realm_name) != 0) {
        gss_log(ISC_LOG_ERROR, "Unable to get krb5 default realm");
        krb5_free_context(krb5_ctx);
        return;
    }
    p = strchr(gss_name, '@');
    if (p == NULL) {
        gss_log(ISC_LOG_ERROR, "badly formatted "
            "tkey-gssapi-credentials (%s)", gss_name);
        krb5_free_context(krb5_ctx);
        return;
    }
    if (strcasecmp(p + 1, krb5_realm_name) != 0) {
        gss_log(ISC_LOG_ERROR, "default realm from krb5.conf (%s) "
            "does not match tkey-gssapi-credential (%s)",
            krb5_realm_name, gss_name);
        krb5_free_context(krb5_ctx);
        return;
    }
    krb5_free_context(krb5_ctx);
}
#endif

isc_result_t
dst_gssapi_acquirecred(dns_name_t *name, isc_boolean_t initiate,
               gss_cred_id_t *cred)
{
#ifdef GSSAPI
    isc_result_t result;
    isc_buffer_t namebuf;
    gss_name_t gname;
    gss_buffer_desc gnamebuf;
    unsigned char array[DNS_NAME_MAXTEXT + 1];
    OM_uint32 gret, minor;
    OM_uint32 lifetime;
    gss_cred_usage_t usage;
    char buf[1024];

    REQUIRE(cred != NULL && *cred == NULL);

    /*
     * XXXSRA In theory we could use GSS_C_NT_HOSTBASED_SERVICE
     * here when we're in the acceptor role, which would let us
     * default the hostname and use a compiled in default service
     * name of "DNS", giving one less thing to configure in
     * named.conf.  Unfortunately, this creates a circular
     * dependency due to DNS-based realm lookup in at least one
     * GSSAPI implementation (Heimdal).  Oh well.
     */
    if (name != NULL) {
        isc_buffer_init(&namebuf, array, sizeof(array));
        name_to_gbuffer(name, &namebuf, &gnamebuf);
        gret = gss_import_name(&minor, &gnamebuf,
                       GSS_C_NO_OID, &gname);
        if (gret != GSS_S_COMPLETE) {
            check_config((char *)array);

            gss_log(3, "failed gss_import_name: %s",
                gss_error_tostring(gret, minor, buf,
                           sizeof(buf)));
            return (ISC_R_FAILURE);
        }
    } else
        gname = NULL;

    /* Get the credentials. */
    if (gname != NULL)
        gss_log(3, "acquiring credentials for %s",
            (char *)gnamebuf.value);
    else {
        /* XXXDCL does this even make any sense? */
        gss_log(3, "acquiring credentials for ?");
    }

    if (initiate)
        usage = GSS_C_INITIATE;
    else
        usage = GSS_C_ACCEPT;

    gret = gss_acquire_cred(&minor, gname, GSS_C_INDEFINITE,
                &mech_oid_set, usage, cred, NULL, &lifetime);

    if (gret != GSS_S_COMPLETE) {
        gss_log(3, "failed to acquire %s credentials for %s: %s",
            initiate ? "initiate" : "accept",
            (gname != NULL) ? (char *)gnamebuf.value : "?",
            gss_error_tostring(gret, minor, buf, sizeof(buf)));
        if (gname != NULL)
            check_config((char *)array);
        result = ISC_R_FAILURE;
        goto cleanup;
    }

    gss_log(4, "acquired %s credentials for %s",
        initiate ? "initiate" : "accept",
        (gname != NULL) ? (char *)gnamebuf.value : "?");

    log_cred(*cred);
    result = ISC_R_SUCCESS;

cleanup:
    if (gname != NULL) {
        gret = gss_release_name(&minor, &gname);
        if (gret != GSS_S_COMPLETE)
            gss_log(3, "failed gss_release_name: %s",
                gss_error_tostring(gret, minor, buf,
                           sizeof(buf)));
    }

    return (result);
#else
    REQUIRE(cred != NULL && *cred == NULL);

    UNUSED(name);
    UNUSED(initiate);
    UNUSED(cred);

    return (ISC_R_NOTIMPLEMENTED);
#endif
}

isc_boolean_t
dst_gssapi_identitymatchesrealmkrb5(dns_name_t *signer, dns_name_t *name,
                    dns_name_t *realm)
{
#ifdef GSSAPI
    char sbuf[DNS_NAME_FORMATSIZE];
    char nbuf[DNS_NAME_FORMATSIZE];
    char rbuf[DNS_NAME_FORMATSIZE];
    char *sname;
    char *rname;
    isc_buffer_t buffer;
    isc_result_t result;

    /*
     * It is far, far easier to write the names we are looking at into
     * a string, and do string operations on them.
     */
    isc_buffer_init(&buffer, sbuf, sizeof(sbuf));
    result = dns_name_toprincipal(signer, &buffer);
    RUNTIME_CHECK(result == ISC_R_SUCCESS);
    isc_buffer_putuint8(&buffer, 0);
    if (name != NULL)
        dns_name_format(name, nbuf, sizeof(nbuf));
    dns_name_format(realm, rbuf, sizeof(rbuf));

    /*
     * Find the realm portion.  This is the part after the @.  If it
     * does not exist, we don't have something we like, so we fail our
     * compare.
     */
    rname = strchr(sbuf, '@');
    if (rname == NULL)
        return (isc_boolean_false);
    *rname = '\0';
    rname++;

    /*
     * Find the host portion of the signer's name.  We do this by
     * searching for the first / character.  We then check to make
     * certain the instance name is "host"
     *
     * This will work for
     *    host/example.com@EXAMPLE.COM
     */
    sname = strchr(sbuf, '/');
    if (sname == NULL)
        return (isc_boolean_false);
    *sname = '\0';
    sname++;
    if (strcmp(sbuf, "host") != 0)
        return (isc_boolean_false);

    /*
     * Now, we do a simple comparison between the name and the realm.
     */
    if (name != NULL) {
        if ((strcasecmp(sname, nbuf) == 0)
            && (strcmp(rname, rbuf) == 0))
            return (isc_boolean_true);
    } else {
        if (strcmp(rname, rbuf) == 0)
            return (isc_boolean_true);
    }

    return (isc_boolean_false);
#else
    UNUSED(signer);
    UNUSED(name);
    UNUSED(realm);
    return (isc_boolean_false);
#endif
}

isc_boolean_t
dst_gssapi_identitymatchesrealmms(dns_name_t *signer, dns_name_t *name,
                  dns_name_t *realm)
{
#ifdef GSSAPI
    char sbuf[DNS_NAME_FORMATSIZE];
    char nbuf[DNS_NAME_FORMATSIZE];
    char rbuf[DNS_NAME_FORMATSIZE];
    char *sname;
    char *nname;
    char *rname;
    isc_buffer_t buffer;
    isc_result_t result;

    /*
     * It is far, far easier to write the names we are looking at into
     * a string, and do string operations on them.
     */
    isc_buffer_init(&buffer, sbuf, sizeof(sbuf));
    result = dns_name_toprincipal(signer, &buffer);
    RUNTIME_CHECK(result == ISC_R_SUCCESS);
    isc_buffer_putuint8(&buffer, 0);
    if (name != NULL)
        dns_name_format(name, nbuf, sizeof(nbuf));
    dns_name_format(realm, rbuf, sizeof(rbuf));

    /*
     * Find the realm portion.  This is the part after the @.  If it
     * does not exist, we don't have something we like, so we fail our
     * compare.
     */
    rname = strchr(sbuf, '@');
    if (rname == NULL)
        return (isc_boolean_false);
    sname = strchr(sbuf, '$');
    if (sname == NULL)
        return (isc_boolean_false);

    /*
     * Verify that the $ and @ follow one another.
     */
    if (rname - sname != 1)
        return (isc_boolean_false);

    /*
     * Find the host portion of the signer's name.  Zero out the $ so
     * it terminates the signer's name, and skip past the @ for
     * the realm.
     *
     * All service principals in Microsoft format seem to be in
     *    machinename$@EXAMPLE.COM
     * format.
     */
    rname++;
    *sname = '\0';
    sname = sbuf;

    /*
     * Find the first . in the target name, and make it the end of
     * the string.   The rest of the name has to match the realm.
     */
    if (name != NULL) {
        nname = strchr(nbuf, '.');
        if (nname == NULL)
            return (isc_boolean_false);
        *nname++ = '\0';
    }

    /*
     * Now, we do a simple comparison between the name and the realm.
     */
    if (name != NULL) {
        if ((strcasecmp(sname, nbuf) == 0)
            && (strcmp(rname, rbuf) == 0)
            && (strcasecmp(nname, rbuf) == 0))
            return (isc_boolean_true);
    } else {
        if (strcmp(rname, rbuf) == 0)
            return (isc_boolean_true);
    }


    return (isc_boolean_false);
#else
    UNUSED(signer);
    UNUSED(name);
    UNUSED(realm);
    return (isc_boolean_false);
#endif
}

isc_result_t
dst_gssapi_releasecred(gss_cred_id_t *cred) {
#ifdef GSSAPI
    OM_uint32 gret, minor;
    char buf[1024];

    REQUIRE(cred != NULL && *cred != NULL);

    gret = gss_release_cred(&minor, cred);
    if (gret != GSS_S_COMPLETE) {
        /* Log the error, but still free the credential's memory */
        gss_log(3, "failed releasing credential: %s",
            gss_error_tostring(gret, minor, buf, sizeof(buf)));
    }
    *cred = NULL;

    return(ISC_R_SUCCESS);
#else
    UNUSED(cred);

    return (ISC_R_NOTIMPLEMENTED);
#endif
}

#ifdef GSSAPI
/*
 * Format a gssapi error message info into a char ** on the given memory
 * context. This is used to return gssapi error messages back up the
 * call chain for reporting to the user.
 */
static void
gss_err_message(isc_mem_t *mctx, isc_uint32_t major, isc_uint32_t minor,
        char **err_message)
{
    char buf[1024];
    char *estr;

    if (err_message == NULL || mctx == NULL) {
        /* the caller doesn't want any error messages */
        return;
    }

    estr = gss_error_tostring(major, minor, buf, sizeof(buf));
    if (estr != NULL)
        (*err_message) = isc_mem_strdup(mctx, estr);
}
#endif

isc_result_t
dst_gssapi_initctx(dns_name_t *name, isc_buffer_t *intoken,
           isc_buffer_t *outtoken, gss_ctx_id_t *gssctx,
           isc_mem_t *mctx, char **err_message)
{
#ifdef GSSAPI
    isc_region_t r;
    isc_buffer_t namebuf;
    gss_name_t gname;
    OM_uint32 gret, minor, ret_flags, flags;
    gss_buffer_desc gintoken, *gintokenp, gouttoken = GSS_C_EMPTY_BUFFER;
    isc_result_t result;
    gss_buffer_desc gnamebuf;
    unsigned char array[DNS_NAME_MAXTEXT + 1];

    /* Client must pass us a valid gss_ctx_id_t here */
    REQUIRE(gssctx != NULL);
    REQUIRE(mctx != NULL);

    isc_buffer_init(&namebuf, array, sizeof(array));
    name_to_gbuffer(name, &namebuf, &gnamebuf);

    /* Get the name as a GSS name */
    gret = gss_import_name(&minor, &gnamebuf, GSS_C_NO_OID, &gname);
    if (gret != GSS_S_COMPLETE) {
        gss_err_message(mctx, gret, minor, err_message);
        result = ISC_R_FAILURE;
        goto out;
    }

    if (intoken != NULL) {
        /* Don't call gss_release_buffer for gintoken! */
        REGION_TO_GBUFFER(*intoken, gintoken);
        gintokenp = &gintoken;
    } else {
        gintokenp = NULL;
    }

    /*
     * Note that we don't set GSS_C_SEQUENCE_FLAG as Windows DNS
     * servers don't like it.
     */
    flags = GSS_C_REPLAY_FLAG | GSS_C_MUTUAL_FLAG | GSS_C_INTEG_FLAG;

    gret = gss_init_sec_context(&minor, GSS_C_NO_CREDENTIAL, gssctx,
                    gname, GSS_SPNEGO_MECHANISM, flags,
                    0, NULL, gintokenp,
                    NULL, &gouttoken, &ret_flags, NULL);

    if (gret != GSS_S_COMPLETE && gret != GSS_S_CONTINUE_NEEDED) {
        gss_err_message(mctx, gret, minor, err_message);
        if (err_message != NULL && *err_message != NULL)
            gss_log(3, "Failure initiating security context: %s",
                *err_message);
        else
            gss_log(3, "Failure initiating security context");

        result = ISC_R_FAILURE;
        goto out;
    }

    /*
     * XXXSRA Not handled yet: RFC 3645 3.1.1: check ret_flags
     * MUTUAL and INTEG flags, fail if either not set.
     */

    /*
     * RFC 2744 states the a valid output token has a non-zero length.
     */
    if (gouttoken.length != 0U) {
        GBUFFER_TO_REGION(gouttoken, r);
        RETERR(isc_buffer_copyregion(outtoken, &r));
    }

    if (gret == GSS_S_COMPLETE)
        result = ISC_R_SUCCESS;
    else
        result = DNS_R_CONTINUE;

 out:
    if (gouttoken.length != 0U)
        (void)gss_release_buffer(&minor, &gouttoken);
    (void)gss_release_name(&minor, &gname);
    return (result);
#else
    UNUSED(name);
    UNUSED(intoken);
    UNUSED(outtoken);
    UNUSED(gssctx);
    UNUSED(mctx);
    UNUSED(err_message);

    return (ISC_R_NOTIMPLEMENTED);
#endif
}

isc_result_t
dst_gssapi_acceptctx(gss_cred_id_t cred,
             const char *gssapi_keytab,
             isc_region_t *intoken, isc_buffer_t **outtoken,
             gss_ctx_id_t *ctxout, dns_name_t *principal,
             isc_mem_t *mctx)
{
#ifdef GSSAPI
    isc_region_t r;
    isc_buffer_t namebuf;
    gss_buffer_desc gnamebuf = GSS_C_EMPTY_BUFFER, gintoken,
            gouttoken = GSS_C_EMPTY_BUFFER;
    OM_uint32 gret, minor;
    gss_ctx_id_t context = GSS_C_NO_CONTEXT;
    gss_name_t gname = NULL;
    isc_result_t result;
    char buf[1024];

    REQUIRE(outtoken != NULL && *outtoken == NULL);

    REGION_TO_GBUFFER(*intoken, gintoken);

    if (*ctxout == NULL)
        context = GSS_C_NO_CONTEXT;
    else
        context = *ctxout;

    if (gssapi_keytab != NULL) {
#if defined(ISC_PLATFORM_GSSAPI_KRB5_HEADER) || defined(WIN32)
        gret = gsskrb5_register_acceptor_identity(gssapi_keytab);
        if (gret != GSS_S_COMPLETE) {
            gss_log(3, "failed "
                "gsskrb5_register_acceptor_identity(%s): %s",
                gssapi_keytab,
                gss_error_tostring(gret, 0, buf, sizeof(buf)));
            return (DNS_R_INVALIDTKEY);
        }
#else
        /*
         * Minimize memory leakage by only setting KRB5_KTNAME
         * if it needs to change.
         */
        const char *old = getenv("KRB5_KTNAME");
        if (old == NULL || strcmp(old, gssapi_keytab) != 0) {
            char *kt = malloc(strlen(gssapi_keytab) + 13);
            if (kt == NULL)
                return (ISC_R_NOMEMORY);
            sprintf(kt, "KRB5_KTNAME=%s", gssapi_keytab);
            if (putenv(kt) != 0)
                return (ISC_R_NOMEMORY);
        }
#endif
    }

    log_cred(cred);

    gret = gss_accept_sec_context(&minor, &context, cred, &gintoken,
                      GSS_C_NO_CHANNEL_BINDINGS, &gname,
                      NULL, &gouttoken, NULL, NULL, NULL);

    result = ISC_R_FAILURE;

    switch (gret) {
    case GSS_S_COMPLETE:
        result = ISC_R_SUCCESS;
        break;
    case GSS_S_CONTINUE_NEEDED:
        result = DNS_R_CONTINUE;
        break;
    case GSS_S_DEFECTIVE_TOKEN:
    case GSS_S_DEFECTIVE_CREDENTIAL:
    case GSS_S_BAD_SIG:
    case GSS_S_DUPLICATE_TOKEN:
    case GSS_S_OLD_TOKEN:
    case GSS_S_NO_CRED:
    case GSS_S_CREDENTIALS_EXPIRED:
    case GSS_S_BAD_BINDINGS:
    case GSS_S_NO_CONTEXT:
    case GSS_S_BAD_MECH:
    case GSS_S_FAILURE:
        result = DNS_R_INVALIDTKEY;
        /* fall through */
    default:
        gss_log(3, "failed gss_accept_sec_context: %s",
            gss_error_tostring(gret, minor, buf, sizeof(buf)));
        return (result);
    }

    if (gouttoken.length > 0U) {
        RETERR(isc_buffer_allocate(mctx, outtoken,
                       (unsigned int)gouttoken.length));
        GBUFFER_TO_REGION(gouttoken, r);
        RETERR(isc_buffer_copyregion(*outtoken, &r));
        (void)gss_release_buffer(&minor, &gouttoken);
    }

    if (gret == GSS_S_COMPLETE) {
        gret = gss_display_name(&minor, gname, &gnamebuf, NULL);
        if (gret != GSS_S_COMPLETE) {
            gss_log(3, "failed gss_display_name: %s",
                gss_error_tostring(gret, minor,
                           buf, sizeof(buf)));
            RETERR(ISC_R_FAILURE);
        }

        /*
         * Compensate for a bug in Solaris8's implementation
         * of gss_display_name().  Should be harmless in any
         * case, since principal names really should not
         * contain null characters.
         */
        if (gnamebuf.length > 0U &&
            ((char *)gnamebuf.value)[gnamebuf.length - 1] == '\0')
            gnamebuf.length--;

        gss_log(3, "gss-api source name (accept) is %.*s",
            (int)gnamebuf.length, (char *)gnamebuf.value);

        GBUFFER_TO_REGION(gnamebuf, r);
        isc_buffer_init(&namebuf, r.base, r.length);
        isc_buffer_add(&namebuf, r.length);

        RETERR(dns_name_fromtext(principal, &namebuf, dns_rootname,
                     0, NULL));

        if (gnamebuf.length != 0U) {
            gret = gss_release_buffer(&minor, &gnamebuf);
            if (gret != GSS_S_COMPLETE)
                gss_log(3, "failed gss_release_buffer: %s",
                    gss_error_tostring(gret, minor, buf,
                               sizeof(buf)));
        }
    }

    *ctxout = context;

 out:
    if (gname != NULL) {
        gret = gss_release_name(&minor, &gname);
        if (gret != GSS_S_COMPLETE)
            gss_log(3, "failed gss_release_name: %s",
                gss_error_tostring(gret, minor, buf,
                           sizeof(buf)));
    }

    return (result);
#else
    UNUSED(cred);
    UNUSED(gssapi_keytab);
    UNUSED(intoken);
    UNUSED(outtoken);
    UNUSED(ctxout);
    UNUSED(principal);
    UNUSED(mctx);

    return (ISC_R_NOTIMPLEMENTED);
#endif
}

isc_result_t
dst_gssapi_deletectx(isc_mem_t *mctx, gss_ctx_id_t *gssctx)
{
#ifdef GSSAPI
    OM_uint32 gret, minor;
    char buf[1024];

    UNUSED(mctx);

    REQUIRE(gssctx != NULL && *gssctx != NULL);

    /* Delete the context from the GSS provider */
    gret = gss_delete_sec_context(&minor, gssctx, GSS_C_NO_BUFFER);
    if (gret != GSS_S_COMPLETE) {
        /* Log the error, but still free the context's memory */
        gss_log(3, "Failure deleting security context %s",
            gss_error_tostring(gret, minor, buf, sizeof(buf)));
    }
    return(ISC_R_SUCCESS);
#else
    UNUSED(mctx);
    UNUSED(gssctx);
    return (ISC_R_NOTIMPLEMENTED);
#endif
}

char *
gss_error_tostring(isc_uint32_t major, isc_uint32_t minor,
           char *buf, size_t buflen) {
#ifdef GSSAPI
    gss_buffer_desc msg_minor = GSS_C_EMPTY_BUFFER,
            msg_major = GSS_C_EMPTY_BUFFER;
    OM_uint32 msg_ctx, minor_stat;

    /* Handle major status */
    msg_ctx = 0;
    (void)gss_display_status(&minor_stat, major, GSS_C_GSS_CODE,
                 GSS_C_NULL_OID, &msg_ctx, &msg_major);

    /* Handle minor status */
    msg_ctx = 0;
    (void)gss_display_status(&minor_stat, minor, GSS_C_MECH_CODE,
                 GSS_C_NULL_OID, &msg_ctx, &msg_minor);

    snprintf(buf, buflen, "GSSAPI error: Major = %s, Minor = %s.",
        (char *)msg_major.value, (char *)msg_minor.value);

    if (msg_major.length != 0U)
        (void)gss_release_buffer(&minor_stat, &msg_major);
    if (msg_minor.length != 0U)
        (void)gss_release_buffer(&minor_stat, &msg_minor);
    return(buf);
#else
    snprintf(buf, buflen, "GSSAPI error: Major = %u, Minor = %u.",
         major, minor);

    return (buf);
#endif
}

void
gss_log(int level, const char *fmt, ...) {
    va_list ap;

    va_start(ap, fmt);
    isc_log_vwrite(dns_lctx, DNS_LOGCATEGORY_GENERAL,
               DNS_LOGMODULE_TKEY, ISC_LOG_DEBUG(level), fmt, ap);
    va_end(ap);
}

/*! \file */