GSSCredentialSelector.m   [plain text]

/*
 * Copyright (c) 2011 Kungliga Tekniska Högskolan
 * (Royal Institute of Technology, Stockholm, Sweden).
 * All rights reserved.
 *
 * Portions Copyright (c) 2011 Apple Inc. 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.
 *
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``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 INSTITUTE OR CONTRIBUTORS 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.
 */

#import <stdio.h>

#import <Foundation/Foundation.h>
#import <Heimdal/krb5.h>
#import <GSS/gssapi.h>
#import <GSS/gssapi_plugin.h>

#include <syslog.h>
#include <assert.h>

/**
 * Icky code that prints the target name and replace the cred with another cred that hard coded in the module
 */

#define GSSC_MAGIC 0x47111147

struct gsssel_ctx {
    int magic;
};

static const char selectuser[] = "lha@KTH.SE";
static const char *replacenames[] = {
    "host@svn.h5l.org", 
    NULL
};

static gss_cred_id_t
isc_replace_cred(gss_name_t target, gss_OID mech, gss_cred_id_t original_cred, OM_uint32 flags)
{
    OM_uint32 maj_stat, min_stat;
    gss_buffer_desc buffer;
    gss_name_t name;
    gss_cred_id_t newcred;
    bool exchange = false;
    size_t n;

    /*
     * Using gss_display_name() is wrong, however it the best we can
     * do right now.
     *
     * We should use gss_import_name() and then compare the name with
     * gss_compare_name(), the only issue with that is that comparing
     * names fragile and do not work as expected wrt to case of
     * string, and in case or Kerberos, hostbased service gets
     * affected by realm.
     */
    
    maj_stat = gss_display_name(&min_stat, target, &buffer, NULL);
    if (maj_stat == GSS_S_COMPLETE) {
	syslog(LOG_ERR, "ISC-replace-cred target name: %.*s", (int)buffer.length, (char *)buffer.value);
	for (n = 0; replacenames[n]; n++) {
	    if (memmem(buffer.value, buffer.length, replacenames[n], strlen(replacenames[n])) != NULL)
		exchange = true;
	}
	gss_release_buffer(&min_stat, &buffer);
    }
    if (!exchange) {
	syslog(LOG_ERR, "ISC-replace-cred not replacing");
	return NULL;
    }
    
    buffer.value = (char *)(uintptr_t)selectuser;
    buffer.length = strlen(selectuser);
    maj_stat = gss_import_name(&min_stat, &buffer, GSS_C_NT_USER_NAME, &name);
    if (maj_stat != GSS_S_COMPLETE)
	return NULL;
    
    maj_stat = gss_acquire_cred(&min_stat, name, GSS_C_INDEFINITE, GSS_C_NO_OID_SET, GSS_C_INITIATE, 
				&newcred, NULL, NULL);
    gss_release_name(&min_stat, &name);
    if (maj_stat != GSS_S_COMPLETE)
	return NULL;
    
    syslog(LOG_ERR, "ISC-replace-cred replacing cred to: %s", selectuser);
    
    return newcred;
}

static krb5_error_code
gsssel_init(krb5_context context, void **ptr)
{
    struct gsssel_ctx *ctx = calloc(1, sizeof(*ctx));

    if (ctx == NULL)
	return ENOMEM;
    
    ctx->magic = GSSC_MAGIC;

    *ptr = ctx;
    return 0;
}

static void
gsssel_fini(void *ptr)
{
    struct gsssel_ctx *ctx = ptr;
    
    assert(ctx->magic == GSSC_MAGIC);

    free(ctx);
}


gssapi_plugin_ftable gssapi_plugin = {
    GSSAPI_PLUGIN_VERSION_1,
    gsssel_init,
    gsssel_fini,
    "gssapi credential selector",
    0,
    isc_replace_cred
};