heimdal/lib/krb5/fcache.c

/*
 * Copyright (c) 1997 - 2017 Kungliga Tekniska Högskolan
 * (Royal Institute of Technology, Stockholm, Sweden).
 * All rights reserved.
 *
 * Portions Copyright (c) 2009 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.
 */

#include "krb5_locl.h"

typedef struct krb5_fcache{
    char *filename;
    char *tmpfn;
    int version;
}krb5_fcache;

struct fcc_cursor {
    int fd;
    off_t cred_start;
    off_t cred_end;
    krb5_storage *sp;
};

#define KRB5_FCC_FVNO_1 1
#define KRB5_FCC_FVNO_2 2
#define KRB5_FCC_FVNO_3 3
#define KRB5_FCC_FVNO_4 4

#define FCC_TAG_DELTATIME 1

#define FCACHE(X) ((krb5_fcache*)(X)->data.data)

#define FILENAME(X) (FCACHE(X)->filename)
#define TMPFILENAME(X) (FCACHE(X)->tmpfn)

#define FCC_CURSOR(C) ((struct fcc_cursor*)(C))

static krb5_error_code KRB5_CALLCONV
fcc_get_name(krb5_context context,
	     krb5_ccache id,
             const char **name,
             const char **colname,
             const char **sub)
{
    if (FCACHE(id) == NULL)
        return KRB5_CC_NOTFOUND;

    if (name)
        *name = FILENAME(id);
    if (colname)
        *colname = FILENAME(id);
    if (sub)
        *sub = NULL;
    return 0;
}

KRB5_LIB_FUNCTION int KRB5_LIB_CALL
_krb5_xlock(krb5_context context, int fd, krb5_boolean exclusive,
	    const char *filename)
{
    int ret;
#ifdef HAVE_FCNTL
    struct flock l;

    l.l_start = 0;
    l.l_len = 0;
    l.l_type = exclusive ? F_WRLCK : F_RDLCK;
    l.l_whence = SEEK_SET;
    ret = fcntl(fd, F_SETLKW, &l);
#else
    ret = flock(fd, exclusive ? LOCK_EX : LOCK_SH);
#endif
    if(ret < 0)
	ret = errno;
    if(ret == EACCES) /* fcntl can return EACCES instead of EAGAIN */
	ret = EAGAIN;

    switch (ret) {
    case 0:
	break;
    case EINVAL: /* filesystem doesn't support locking, let the user have it */
	ret = 0;
	break;
    case EAGAIN:
	krb5_set_error_message(context, ret,
			       N_("timed out locking cache file %s", "file"),
			       filename);
	break;
    default: {
	char buf[128];
	rk_strerror_r(ret, buf, sizeof(buf));
	krb5_set_error_message(context, ret,
			       N_("error locking cache file %s: %s",
				  "file, error"), filename, buf);
	break;
    }
    }
    return ret;
}

KRB5_LIB_FUNCTION int KRB5_LIB_CALL
_krb5_xunlock(krb5_context context, int fd)
{
    int ret;
#ifdef HAVE_FCNTL
    struct flock l;
    l.l_start = 0;
    l.l_len = 0;
    l.l_type = F_UNLCK;
    l.l_whence = SEEK_SET;
    ret = fcntl(fd, F_SETLKW, &l);
#else
    ret = flock(fd, LOCK_UN);
#endif
    if (ret < 0)
	ret = errno;
    switch (ret) {
    case 0:
	break;
    case EINVAL: /* filesystem doesn't support locking, let the user have it */
	ret = 0;
	break;
    default: {
	char buf[128];
	rk_strerror_r(ret, buf, sizeof(buf));
	krb5_set_error_message(context, ret,
			       N_("Failed to unlock file: %s", ""), buf);
	break;
    }
    }
    return ret;
}

static krb5_error_code
write_storage(krb5_context context, krb5_storage *sp, int fd)
{
    krb5_error_code ret;
    krb5_data data;
    ssize_t sret;

    ret = krb5_storage_to_data(sp, &data);
    if (ret) {
	krb5_set_error_message(context, ret, N_("malloc: out of memory", ""));
	return ret;
    }
    sret = write(fd, data.data, data.length);
    ret = (sret != (ssize_t)data.length);
    krb5_data_free(&data);
    if (ret) {
	ret = errno;
	krb5_set_error_message(context, ret,
			       N_("Failed to write FILE credential data", ""));
	return ret;
    }
    return 0;
}


static krb5_error_code KRB5_CALLCONV
fcc_lock(krb5_context context, krb5_ccache id,
	 int fd, krb5_boolean exclusive)
{
    krb5_error_code ret;
    const char *name;

    if (exclusive == FALSE)
        return 0;
    ret = fcc_get_name(context, id, &name, NULL, NULL);
    if (ret == 0)
        ret = _krb5_xlock(context, fd, exclusive, name);
    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_resolve(krb5_context context,
            krb5_ccache *id,
            const char *res,
            const char *sub)
{
    krb5_fcache *f;

    if (sub && *sub) {
        krb5_set_error_message(context, KRB5_CC_NOSUPP,
                               N_("FILE ccache type is not a collection "
                                  "type", ""));
        return KRB5_CC_NOSUPP;
    }

    f = calloc(1, sizeof(*f));
    if(f == NULL) {
	krb5_set_error_message(context, KRB5_CC_NOMEM,
			       N_("malloc: out of memory", ""));
	return KRB5_CC_NOMEM;
    }
    f->tmpfn = NULL;
    f->filename = strdup(res);
    if(f->filename == NULL){
	free(f);
	krb5_set_error_message(context, KRB5_CC_NOMEM,
			       N_("malloc: out of memory", ""));
	return KRB5_CC_NOMEM;
    }
    f->version = 0;
    (*id)->data.data = f;
    (*id)->data.length = sizeof(*f);

    return 0;
}

/*
 * Try to scrub the contents of `filename' safely.
 */

static int
scrub_file (int fd)
{
    off_t pos;
    char buf[128];

    pos = lseek(fd, 0, SEEK_END);
    if (pos < 0)
        return errno;
    if (lseek(fd, 0, SEEK_SET) < 0)
        return errno;
    memset(buf, 0, sizeof(buf));
    while(pos > 0) {
	ssize_t tmp;
	size_t wr = sizeof(buf);
	if (wr > pos)
	    wr = (size_t)pos;
        tmp = write(fd, buf, wr);

	if (tmp < 0)
	    return errno;
	pos -= tmp;
    }
#ifdef _MSC_VER
    _commit (fd);
#else
    fsync (fd);
#endif
    return 0;
}

/*
 * Erase `filename' if it exists, trying to remove the contents if
 * it's `safe'.  We always try to remove the file, it it exists.  It's
 * only overwritten if it's a regular file (not a symlink and not a
 * hardlink)
 */

KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
_krb5_erase_file(krb5_context context, const char *filename)
{
    int fd;
    struct stat sb1, sb2;
    int ret;

    ret = lstat (filename, &sb1);
    if (ret < 0) {
	if(errno == ENOENT)
	    return 0;
	else
	    return errno;
    }

    fd = open(filename, O_RDWR | O_BINARY | O_CLOEXEC | O_NOFOLLOW);
    if(fd < 0) {
	if(errno == ENOENT)
	    return 0;
	else
	    return errno;
    }
    rk_cloexec(fd);
    ret = _krb5_xlock(context, fd, 1, filename);
    if (ret) {
	close(fd);
	return ret;
    }
    if (unlink(filename) < 0) {
	ret = errno;
        close (fd);
	krb5_set_error_message(context, errno,
	    N_("krb5_cc_destroy: unlinking \"%s\": %s", ""),
	    filename, strerror(ret));
        return ret;
    }
    ret = fstat(fd, &sb2);
    if (ret < 0) {
	ret = errno;
	close (fd);
	return ret;
    }

    /* check if someone was playing with symlinks */

    if (sb1.st_dev != sb2.st_dev || sb1.st_ino != sb2.st_ino) {
	close(fd);
	return EPERM;
    }

    /* there are still hard links to this file */

    if (sb2.st_nlink != 0) {
        close(fd);
        return 0;
    }

    ret = scrub_file(fd);
    close(fd);
    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_gen_new(krb5_context context, krb5_ccache *id)
{
    char *file = NULL, *exp_file = NULL;
    krb5_error_code ret;
    krb5_fcache *f;
    int fd;

    f = calloc(1, sizeof(*f));
    if(f == NULL) {
	krb5_set_error_message(context, KRB5_CC_NOMEM,
			       N_("malloc: out of memory", ""));
	return KRB5_CC_NOMEM;
    }
    f->tmpfn = NULL;
    ret = asprintf(&file, "%sXXXXXX", KRB5_DEFAULT_CCFILE_ROOT);
    if(ret < 0 || file == NULL) {
	free(f);
	krb5_set_error_message(context, KRB5_CC_NOMEM,
			       N_("malloc: out of memory", ""));
	return KRB5_CC_NOMEM;
    }
    ret = _krb5_expand_path_tokens(context, file, 1, &exp_file);
    free(file);
    if (ret) {
	free(f);
	return ret;
    }

    file = exp_file;

    fd = mkostemp(exp_file, O_CLOEXEC);
    if(fd < 0) {
	ret = (krb5_error_code)errno;
	krb5_set_error_message(context, ret, N_("mkstemp %s failed", ""), exp_file);
	free(f);
	free(exp_file);
	return ret;
    }
    close(fd);
    f->filename = exp_file;
    f->version = 0;
    (*id)->data.data = f;
    (*id)->data.length = sizeof(*f);
    return 0;
}

static void
storage_set_flags(krb5_context context, krb5_storage *sp, int vno)
{
    int flags = 0;
    switch(vno) {
    case KRB5_FCC_FVNO_1:
	flags |= KRB5_STORAGE_PRINCIPAL_WRONG_NUM_COMPONENTS;
	flags |= KRB5_STORAGE_PRINCIPAL_NO_NAME_TYPE;
	flags |= KRB5_STORAGE_HOST_BYTEORDER;
	break;
    case KRB5_FCC_FVNO_2:
	flags |= KRB5_STORAGE_HOST_BYTEORDER;
	break;
    case KRB5_FCC_FVNO_3:
	flags |= KRB5_STORAGE_KEYBLOCK_KEYTYPE_TWICE;
	break;
    case KRB5_FCC_FVNO_4:
	break;
    default:
	krb5_abortx(context,
		    "storage_set_flags called with bad vno (%x)", vno);
    }
    krb5_storage_set_flags(sp, flags);
}

static krb5_error_code KRB5_CALLCONV
fcc_open(krb5_context context,
	 krb5_ccache id,
	 const char *operation,
	 int *fd_ret,
	 int flags,
	 mode_t mode)
{
    krb5_boolean exclusive = ((flags | O_WRONLY) == flags ||
			      (flags | O_RDWR) == flags);
    krb5_error_code ret;
    const char *filename;
    struct stat sb1, sb2;
#ifndef _WIN32
    struct stat sb3;
    size_t tries = 3;
#endif
    int strict_checking;
    int fd;

    flags |= O_BINARY | O_CLOEXEC | O_NOFOLLOW;

    *fd_ret = -1;

    if (FCACHE(id) == NULL)
        return krb5_einval(context, 2);

    if ((flags & O_EXCL)) {
        flags &= ~O_EXCL;
        /*
         * FIXME Instead of mkostemp()... we could instead try to use a .new
         * file... with care.  Or the O_TMPFILE / linkat() extensions.  We need
         * a roken / heimbase abstraction for that.
         */
        if (TMPFILENAME(id))
            (void) unlink(TMPFILENAME(id));
        free(TMPFILENAME(id));
        TMPFILENAME(id) = NULL;
        if (asprintf(&TMPFILENAME(id), "%s-XXXXXX", FILENAME(id)) < 0 ||
            TMPFILENAME(id) == NULL)
            return krb5_enomem(context);
        if ((fd = mkostemp(TMPFILENAME(id), O_CLOEXEC)) == -1) {
            krb5_set_error_message(context, ret = errno,
                                   N_("Could not make temp ccache FILE:%s", ""),
                                   TMPFILENAME(id));
            free(TMPFILENAME(id));
            TMPFILENAME(id) = NULL;
            return ret;
        }
        goto out;
    }

    filename = TMPFILENAME(id) ? TMPFILENAME(id) : FILENAME(id);
    strict_checking = (flags & O_CREAT) == 0 &&
	(context->flags & KRB5_CTX_F_FCACHE_STRICT_CHECKING) != 0;

again:
    memset(&sb1, 0, sizeof(sb1));
    ret = lstat(filename, &sb1);
    if (ret == 0) {
	if (!S_ISREG(sb1.st_mode)) {
	    krb5_set_error_message(context, EPERM,
				   N_("Refuses to open symlinks for caches FILE:%s", ""), filename);
	    return EPERM;
	}
    } else if (errno != ENOENT || !(flags & O_CREAT)) {
	krb5_set_error_message(context, errno, N_("%s lstat(%s)", "file, error"),
			       operation, filename);
	return errno;
    }

    fd = open(filename, flags, mode);
    if(fd < 0) {
	char buf[128];
	ret = errno;
	rk_strerror_r(ret, buf, sizeof(buf));
	krb5_set_error_message(context, ret, N_("%s open(%s): %s", "file, error"),
			       operation, filename, buf);
	return ret;
    }
    rk_cloexec(fd);

    ret = fstat(fd, &sb2);
    if (ret < 0) {
	krb5_clear_error_message(context);
	close(fd);
	return errno;
    }

    if (!S_ISREG(sb2.st_mode)) {
	krb5_set_error_message(context, EPERM, N_("Refuses to open non files caches: FILE:%s", ""), filename);
	close(fd);
	return EPERM;
    }

#ifndef _WIN32
    if (sb1.st_dev && sb1.st_ino &&
	(sb1.st_dev != sb2.st_dev || sb1.st_ino != sb2.st_ino)) {
	/*
	 * Perhaps we raced with a rename().  To complain about
	 * symlinks in that case would cause unnecessary concern, so
	 * we check for that possibility and loop.  This has no
	 * TOCTOU problems because we redo the open().  We could also
	 * not do any of this checking if O_NOFOLLOW != 0...
	 */
	close(fd);
	ret = lstat(filename, &sb3);
	if (ret || sb1.st_dev != sb2.st_dev ||
	    sb3.st_dev != sb2.st_dev || sb3.st_ino != sb2.st_ino) {
	    krb5_set_error_message(context, EPERM, N_("Refuses to open possible symlink for caches: FILE:%s", ""), filename);
	    return EPERM;
	}
	if (--tries == 0) {
	    krb5_set_error_message(context, EPERM, N_("Raced too many times with renames of FILE:%s", ""), filename);
	    return EPERM;
	}
	goto again;
    }
#endif

    /*
     * /tmp (or wherever default ccaches go) might not be on its own
     * filesystem, or on a filesystem different /etc, say, and even if
     * it were, suppose a user hard-links another's ccache to her
     * default ccache, then runs a set-uid program that will user her
     * default ccache (even if it ignores KRB5CCNAME)...
     *
     * Default ccache locations should really be on per-user non-tmp
     * locations on tmpfs "run" directories.  But we don't know here
     * that this is the case.  Thus: no hard-links, no symlinks.
     */
    if (sb2.st_nlink != 1) {
	krb5_set_error_message(context, EPERM, N_("Refuses to open hardlinks for caches FILE:%s", ""), filename);
	close(fd);
	return EPERM;
    }

    if (strict_checking) {
#ifndef _WIN32
	/*
	 * XXX WIN32: Needs to have ACL checking code!
	 * st_mode comes out as 100666, and st_uid is no use.
	 */
	/*
	 * XXX Should probably add options to improve control over this
	 * check.  We might want strict checking of everything except
	 * this.
	 */
	if (sb2.st_uid != geteuid()) {
	    krb5_set_error_message(context, EPERM, N_("Refuses to open cache files not own by myself FILE:%s (owned by %d)", ""), filename, (int)sb2.st_uid);
	    close(fd);
	    return EPERM;
	}
	if ((sb2.st_mode & 077) != 0) {
	    krb5_set_error_message(context, EPERM,
				   N_("Refuses to open group/other readable files FILE:%s", ""), filename);
	    close(fd);
	    return EPERM;
	}
#endif
    }

out:
    if((ret = fcc_lock(context, id, fd, exclusive)) != 0) {
	close(fd);
	return ret;
    }
    *fd_ret = fd;
    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_initialize(krb5_context context,
	       krb5_ccache id,
	       krb5_principal primary_principal)
{
    krb5_fcache *f = FCACHE(id);
    int ret = 0;
    int fd;

    if (f == NULL)
        return krb5_einval(context, 2);

    /*
     * fcc_open() will notice the O_EXCL and will make a temporary file that
     * will later be renamed into place.
     */
    ret = fcc_open(context, id, "initialize", &fd, O_RDWR | O_CREAT | O_EXCL, 0600);
    if(ret)
	return ret;
    {
	krb5_storage *sp;
	sp = krb5_storage_emem();
	if (sp == NULL)
	    return krb5_enomem(context);
	krb5_storage_set_eof_code(sp, KRB5_CC_END);
	if(context->fcache_vno != 0)
	    f->version = context->fcache_vno;
	else
	    f->version = KRB5_FCC_FVNO_4;
        if (ret == 0)
            ret = krb5_store_int8(sp, 5);
        if (ret == 0)
            ret = krb5_store_int8(sp, f->version);
	storage_set_flags(context, sp, f->version);
	if(f->version == KRB5_FCC_FVNO_4 && ret == 0) {
	    /* V4 stuff */
	    if (context->kdc_sec_offset) {
                if (ret == 0)
                    ret = krb5_store_int16 (sp, 12); /* length */
                if (ret == 0)
                    ret = krb5_store_int16 (sp, FCC_TAG_DELTATIME); /* Tag */
                if (ret == 0)
                    ret = krb5_store_int16 (sp, 8); /* length of data */
                if (ret == 0)
                    ret = krb5_store_int32 (sp, context->kdc_sec_offset);
                if (ret == 0)
                    ret = krb5_store_int32 (sp, context->kdc_usec_offset);
	    } else {
                if (ret == 0)
                    ret = krb5_store_int16 (sp, 0);
	    }
	}
        if (ret == 0)
            ret = krb5_store_principal(sp, primary_principal);

        if (ret == 0)
            ret = write_storage(context, sp, fd);

	krb5_storage_free(sp);
    }
    if (close(fd) < 0)
	if (ret == 0) {
	    char buf[128];
	    ret = errno;
	    rk_strerror_r(ret, buf, sizeof(buf));
	    krb5_set_error_message(context, ret, N_("close %s: %s", ""),
				   FILENAME(id), buf);
	}
    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_close(krb5_context context,
	  krb5_ccache id)
{
    if (FCACHE(id) == NULL)
        return krb5_einval(context, 2);

    if (TMPFILENAME(id))
        (void) unlink(TMPFILENAME(id));
    free(TMPFILENAME(id));
    free(FILENAME(id));
    krb5_data_free(&id->data);
    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_destroy(krb5_context context,
	    krb5_ccache id)
{
    if (FCACHE(id) == NULL)
        return krb5_einval(context, 2);

    if (TMPFILENAME(id))
        (void) _krb5_erase_file(context, TMPFILENAME(id));
    return _krb5_erase_file(context, FILENAME(id));
}

static krb5_error_code KRB5_CALLCONV
fcc_store_cred(krb5_context context,
	       krb5_ccache id,
	       krb5_creds *creds)
{
    int ret;
    int fd;

    ret = fcc_open(context, id, "store", &fd, O_WRONLY | O_APPEND, 0);
    if(ret)
	return ret;
    {
	krb5_storage *sp;

	sp = krb5_storage_emem();
	if (sp == NULL)
	    return krb5_enomem(context);
	krb5_storage_set_eof_code(sp, KRB5_CC_END);
	storage_set_flags(context, sp, FCACHE(id)->version);
	ret = krb5_store_creds(sp, creds);
	if (ret == 0)
	    ret = write_storage(context, sp, fd);
	krb5_storage_free(sp);
    }
    if (close(fd) < 0) {
	if (ret == 0) {
	    char buf[128];
	    ret = errno;
	    rk_strerror_r(ret, buf, sizeof(buf));
	    krb5_set_error_message(context, ret, N_("close %s: %s", ""),
				   FILENAME(id), buf);
	}
    }
    if (ret == 0 && TMPFILENAME(id) &&
        !krb5_is_config_principal(context, creds->server)) {

        /*
         * Portability note: there's no need to have WIN32 or other code here
         * for odd rename cases because rk_rename() is meant to handle that.
         */
        ret = rk_rename(TMPFILENAME(id), FILENAME(id));
        if (ret == 0) {
            free(TMPFILENAME(id));
            TMPFILENAME(id) = NULL;
        } else {
            ret = errno;
        }
    }
    return ret;
}

static krb5_error_code
init_fcc(krb5_context context,
	 krb5_ccache id,
	 const char *operation,
	 krb5_storage **ret_sp,
	 int *ret_fd,
	 krb5_deltat *kdc_offset)
{
    int fd;
    int8_t pvno, tag;
    krb5_storage *sp;
    krb5_error_code ret;

    *ret_fd = -1;
    *ret_sp = NULL;
    if (kdc_offset)
	*kdc_offset = 0;

    ret = fcc_open(context, id, operation, &fd, O_RDONLY, 0);
    if(ret)
	return ret;

    sp = krb5_storage_stdio_from_fd(fd, "r");
    if(sp == NULL) {
	krb5_clear_error_message(context);
	ret = ENOMEM;
	goto out;
    }
    krb5_storage_set_eof_code(sp, KRB5_CC_END);
    ret = krb5_ret_int8(sp, &pvno);
    if (ret != 0) {
	if(ret == KRB5_CC_END) {
	    ret = ENOENT;
	    krb5_set_error_message(context, ret,
				   N_("Empty credential cache file: %s", ""),
				   FILENAME(id));
	} else
	    krb5_set_error_message(context, ret, N_("Error reading pvno "
						    "in cache file: %s", ""),
				   FILENAME(id));
	goto out;
    }
    if (pvno != 5) {
	ret = KRB5_CCACHE_BADVNO;
	krb5_set_error_message(context, ret, N_("Bad version number in credential "
						"cache file: %s", ""),
			       FILENAME(id));
	goto out;
    }
    ret = krb5_ret_int8(sp, &tag); /* should not be host byte order */
    if (ret != 0) {
	ret = KRB5_CC_FORMAT;
	krb5_set_error_message(context, ret, "Error reading tag in "
			      "cache file: %s", FILENAME(id));
	goto out;
    }
    FCACHE(id)->version = tag;
    storage_set_flags(context, sp, FCACHE(id)->version);
    switch (tag) {
    case KRB5_FCC_FVNO_4: {
	int16_t length;

	ret = krb5_ret_int16 (sp, &length);
	if(ret) {
	    ret = KRB5_CC_FORMAT;
	    krb5_set_error_message(context, ret,
				   N_("Error reading tag length in "
				      "cache file: %s", ""), FILENAME(id));
	    goto out;
	}
	while(length > 0) {
	    int16_t dtag, data_len;
	    int i;
	    int8_t dummy;

	    ret = krb5_ret_int16 (sp, &dtag);
	    if(ret) {
		ret = KRB5_CC_FORMAT;
		krb5_set_error_message(context, ret, N_("Error reading dtag in "
							"cache file: %s", ""),
				       FILENAME(id));
		goto out;
	    }
	    ret = krb5_ret_int16 (sp, &data_len);
	    if(ret) {
		ret = KRB5_CC_FORMAT;
		krb5_set_error_message(context, ret,
				       N_("Error reading dlength "
					  "in cache file: %s",""),
				       FILENAME(id));
		goto out;
	    }
	    switch (dtag) {
	    case FCC_TAG_DELTATIME : {
		int32_t offset;

		ret = krb5_ret_int32 (sp, &offset);
		ret |= krb5_ret_int32 (sp, &context->kdc_usec_offset);
		if(ret) {
		    ret = KRB5_CC_FORMAT;
		    krb5_set_error_message(context, ret,
					   N_("Error reading kdc_sec in "
					      "cache file: %s", ""),
					   FILENAME(id));
		    goto out;
		}
		context->kdc_sec_offset = offset;
		if (kdc_offset)
		    *kdc_offset = offset;
		break;
	    }
	    default :
		for (i = 0; i < data_len; ++i) {
		    ret = krb5_ret_int8 (sp, &dummy);
		    if(ret) {
			ret = KRB5_CC_FORMAT;
			krb5_set_error_message(context, ret,
					       N_("Error reading unknown "
						  "tag in cache file: %s", ""),
					       FILENAME(id));
			goto out;
		    }
		}
		break;
	    }
	    length -= 4 + data_len;
	}
	break;
    }
    case KRB5_FCC_FVNO_3:
    case KRB5_FCC_FVNO_2:
    case KRB5_FCC_FVNO_1:
	break;
    default :
	ret = KRB5_CCACHE_BADVNO;
	krb5_set_error_message(context, ret,
			       N_("Unknown version number (%d) in "
				  "credential cache file: %s", ""),
			       (int)tag, FILENAME(id));
	goto out;
    }
    *ret_sp = sp;
    *ret_fd = fd;

    return 0;
  out:
    if(sp != NULL)
	krb5_storage_free(sp);
    close(fd);
    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_get_principal(krb5_context context,
		  krb5_ccache id,
		  krb5_principal *principal)
{
    krb5_error_code ret;
    int fd;
    krb5_storage *sp;

    ret = init_fcc (context, id, "get-principal", &sp, &fd, NULL);
    if (ret)
	return ret;
    ret = krb5_ret_principal(sp, principal);
    if (ret)
	krb5_clear_error_message(context);
    krb5_storage_free(sp);
    close(fd);
    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_end_get (krb5_context context,
	     krb5_ccache id,
	     krb5_cc_cursor *cursor);

static krb5_error_code KRB5_CALLCONV
fcc_get_first (krb5_context context,
	       krb5_ccache id,
	       krb5_cc_cursor *cursor)
{
    krb5_error_code ret;
    krb5_principal principal;

    if (FCACHE(id) == NULL)
        return krb5_einval(context, 2);

    *cursor = calloc(1, sizeof(struct fcc_cursor));
    if (*cursor == NULL) {
        krb5_set_error_message(context, ENOMEM, N_("malloc: out of memory", ""));
	return ENOMEM;
    }

    ret = init_fcc(context, id, "get-first", &FCC_CURSOR(*cursor)->sp,
		   &FCC_CURSOR(*cursor)->fd, NULL);
    if (ret) {
	free(*cursor);
	*cursor = NULL;
	return ret;
    }
    ret = krb5_ret_principal (FCC_CURSOR(*cursor)->sp, &principal);
    if(ret) {
	krb5_clear_error_message(context);
	fcc_end_get(context, id, cursor);
	return ret;
    }
    krb5_free_principal (context, principal);
    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_get_next (krb5_context context,
	      krb5_ccache id,
	      krb5_cc_cursor *cursor,
	      krb5_creds *creds)
{
    krb5_error_code ret;

    if (FCACHE(id) == NULL)
        return krb5_einval(context, 2);

    if (FCC_CURSOR(*cursor) == NULL)
        return krb5_einval(context, 3);

    FCC_CURSOR(*cursor)->cred_start =
        krb5_storage_seek(FCC_CURSOR(*cursor)->sp, 0, SEEK_CUR);

    ret = krb5_ret_creds(FCC_CURSOR(*cursor)->sp, creds);
    if (ret)
	krb5_clear_error_message(context);

    FCC_CURSOR(*cursor)->cred_end =
        krb5_storage_seek(FCC_CURSOR(*cursor)->sp, 0, SEEK_CUR);

    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_end_get (krb5_context context,
	     krb5_ccache id,
	     krb5_cc_cursor *cursor)
{

    if (FCACHE(id) == NULL)
        return krb5_einval(context, 2);

    if (FCC_CURSOR(*cursor) == NULL)
        return krb5_einval(context, 3);

    krb5_storage_free(FCC_CURSOR(*cursor)->sp);
    close (FCC_CURSOR(*cursor)->fd);
    free(*cursor);
    *cursor = NULL;
    return 0;
}

static void KRB5_CALLCONV
cred_delete(krb5_context context,
	    krb5_ccache id,
	    krb5_cc_cursor *cursor,
	    krb5_creds *cred)
{
    krb5_error_code ret;
    krb5_storage *sp;
    krb5_data orig_cred_data;
    unsigned char *cred_data_in_file = NULL;
    off_t new_cred_sz;
    struct stat sb1, sb2;
    int fd = -1;
    ssize_t bytes;
    krb5_const_realm srealm = krb5_principal_get_realm(context, cred->server);

    /* This is best-effort code; if we lose track of errors here it's OK */

    heim_assert(FCC_CURSOR(*cursor)->cred_start < FCC_CURSOR(*cursor)->cred_end,
		"fcache internal error");

    krb5_data_zero(&orig_cred_data);

    sp = krb5_storage_emem();
    if (sp == NULL)
	return;
    krb5_storage_set_eof_code(sp, KRB5_CC_END);
    storage_set_flags(context, sp, FCACHE(id)->version);

    /* Get a copy of what the cred should look like in the file; see below */
    ret = krb5_store_creds(sp, cred);
    if (ret)
	goto out;

    ret = krb5_storage_to_data(sp, &orig_cred_data);
    if (ret)
	goto out;
    krb5_storage_free(sp);

    cred_data_in_file = malloc(orig_cred_data.length);
    if (cred_data_in_file == NULL)
	goto out;

    /*
     * Mark the cred expired; krb5_cc_retrieve_cred() callers should use
     * KRB5_TC_MATCH_TIMES, so this should be good enough...
     */
    cred->times.endtime = 0;

    /* ...except for config creds because we don't check their endtimes */
    if (srealm && strcmp(srealm, "X-CACHECONF:") == 0) {
	ret = krb5_principal_set_realm(context, cred->server, "X-RMED-CONF:");
	if (ret)
	    goto out;
    }

    sp = krb5_storage_emem();
    if (sp == NULL)
	goto out;
    krb5_storage_set_eof_code(sp, KRB5_CC_END);
    storage_set_flags(context, sp, FCACHE(id)->version);

    ret = krb5_store_creds(sp, cred);

    /* The new cred must be the same size as the old cred */
    new_cred_sz = krb5_storage_seek(sp, 0, SEEK_END);
    if (new_cred_sz != orig_cred_data.length || new_cred_sz !=
	(FCC_CURSOR(*cursor)->cred_end - FCC_CURSOR(*cursor)->cred_start)) {
	/* XXX This really can't happen.  Assert like above? */
	krb5_set_error_message(context, EINVAL,
			       N_("Credential deletion failed on ccache "
				  "FILE:%s: new credential size did not "
				  "match old credential size", ""),
			       FILENAME(id));
	goto out;
    }

    ret = fcc_open(context, id, "remove_cred", &fd, O_RDWR, 0);
    if (ret)
	goto out;

    /*
     * Check that we're updating the same file where we got the
     * cred's offset, else we'd be corrupting a new ccache.
     */
    if (fstat(FCC_CURSOR(*cursor)->fd, &sb1) == -1 ||
	fstat(fd, &sb2) == -1)
	goto out;
    if (sb1.st_dev != sb2.st_dev || sb1.st_ino != sb2.st_ino)
	goto out;

    /*
     * Make sure what we overwrite is what we expected.
     *
     * FIXME: We *really* need the ccache v4 tag for ccache ID.  This
     * check that we're only overwriting something that looks exactly
     * like what we want to is probably good enough in practice, but
     * it's not guaranteed to work.
     */
    if (lseek(fd, FCC_CURSOR(*cursor)->cred_start, SEEK_SET) == (off_t)-1)
	goto out;
    bytes = read(fd, cred_data_in_file, orig_cred_data.length);
    if (bytes != orig_cred_data.length)
	goto out;
    if (memcmp(orig_cred_data.data, cred_data_in_file, bytes) != 0)
	goto out;
    if (lseek(fd, FCC_CURSOR(*cursor)->cred_start, SEEK_SET) == (off_t)-1)
	goto out;
    ret = write_storage(context, sp, fd);
out:
    if (fd > -1) {
	if (close(fd) < 0 && ret == 0) {
	    krb5_set_error_message(context, errno, N_("close %s", ""),
				   FILENAME(id));
	}
    }
    krb5_data_free(&orig_cred_data);
    free(cred_data_in_file);
    krb5_storage_free(sp);
    return;
}

static krb5_error_code KRB5_CALLCONV
fcc_remove_cred(krb5_context context,
		krb5_ccache id,
		krb5_flags which,
		krb5_creds *mcred)
{
    krb5_error_code ret, ret2;
    krb5_cc_cursor cursor;
    krb5_creds found_cred;

    if (FCACHE(id) == NULL)
	return krb5_einval(context, 2);

    ret = krb5_cc_start_seq_get(context, id, &cursor);
    if (ret)
	return ret;
    while ((ret = krb5_cc_next_cred(context, id, &cursor, &found_cred)) == 0) {
	if (!krb5_compare_creds(context, which, mcred, &found_cred)) {
            krb5_free_cred_contents(context, &found_cred);
	    continue;
        }
	cred_delete(context, id, &cursor, &found_cred);
	krb5_free_cred_contents(context, &found_cred);
    }
    ret2 = krb5_cc_end_seq_get(context, id, &cursor);
    if (ret == 0)
	return ret2;
    if (ret == KRB5_CC_END)
	return 0;
    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_set_flags(krb5_context context,
	      krb5_ccache id,
	      krb5_flags flags)
{
    if (FCACHE(id) == NULL)
        return krb5_einval(context, 2);

    return 0; /* XXX */
}

static int KRB5_CALLCONV
fcc_get_version(krb5_context context,
		krb5_ccache id)
{
    if (FCACHE(id) == NULL)
        return -1;

    return FCACHE(id)->version;
}

struct fcache_iter {
    int first;
};

static krb5_error_code KRB5_CALLCONV
fcc_get_cache_first(krb5_context context, krb5_cc_cursor *cursor)
{
    struct fcache_iter *iter;

    iter = calloc(1, sizeof(*iter));
    if (iter == NULL) {
	krb5_set_error_message(context, ENOMEM, N_("malloc: out of memory", ""));
	return ENOMEM;
    }
    iter->first = 1;
    *cursor = iter;
    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_get_cache_next(krb5_context context, krb5_cc_cursor cursor, krb5_ccache *id)
{
    struct fcache_iter *iter = cursor;
    krb5_error_code ret;
    const char *fn, *cc_type;
    krb5_ccache cc;

    if (iter == NULL)
        return krb5_einval(context, 2);

    if (!iter->first) {
	krb5_clear_error_message(context);
	return KRB5_CC_END;
    }
    iter->first = 0;

    /*
     * Note: do not allow krb5_cc_default_name() to recurse via
     * krb5_cc_cache_match().
     * Note that context->default_cc_name will be NULL even though
     * KRB5CCNAME is set in the environment if
     * krb5_cc_set_default_name() hasn't
     */
    fn = krb5_cc_default_name(context);
    ret = krb5_cc_resolve(context, fn, &cc);
    if (ret != 0)
        return ret;
    cc_type = krb5_cc_get_type(context, cc);
    if (strcmp(cc_type, "FILE") != 0) {
        krb5_cc_close(context, cc);
        return KRB5_CC_END;
    }

    *id = cc;

    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_end_cache_get(krb5_context context, krb5_cc_cursor cursor)
{
    struct fcache_iter *iter = cursor;

    if (iter == NULL)
        return krb5_einval(context, 2);

    free(iter);
    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_move(krb5_context context, krb5_ccache from, krb5_ccache to)
{
    krb5_error_code ret = 0;

    if ((ret = rk_rename(FILENAME(from), FILENAME(to))))
        ret = errno;
    /*
     * We need only close from -- we can't destroy it since the rename
     * succeeded, which "destroyed" it at its old name.
     */
    if (ret == 0)
        krb5_cc_close(context, from);
    return ret;
}

static krb5_error_code KRB5_CALLCONV
fcc_get_default_name(krb5_context context, char **str)
{
    return _krb5_expand_default_cc_name(context,
					KRB5_DEFAULT_CCNAME_FILE,
					str);
}

static krb5_error_code KRB5_CALLCONV
fcc_lastchange(krb5_context context, krb5_ccache id, krb5_timestamp *mtime)
{
    krb5_error_code ret;
    struct stat sb;
    int fd;

    ret = fcc_open(context, id, "lastchange", &fd, O_RDONLY, 0);
    if(ret)
	return ret;
    ret = fstat(fd, &sb);
    close(fd);
    if (ret) {
	ret = errno;
	krb5_set_error_message(context, ret, N_("Failed to stat cache file", ""));
	return ret;
    }
    *mtime = sb.st_mtime;
    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_set_kdc_offset(krb5_context context, krb5_ccache id, krb5_deltat kdc_offset)
{
    return 0;
}

static krb5_error_code KRB5_CALLCONV
fcc_get_kdc_offset(krb5_context context, krb5_ccache id, krb5_deltat *kdc_offset)
{
    krb5_error_code ret;
    krb5_storage *sp = NULL;
    int fd;
    ret = init_fcc(context, id, "get-kdc-offset", &sp, &fd, kdc_offset);
    if (sp)
	krb5_storage_free(sp);
    close(fd);

    return ret;
}


/**
 * Variable containing the FILE based credential cache implemention.
 *
 * @ingroup krb5_ccache
 */

KRB5_LIB_VARIABLE const krb5_cc_ops krb5_fcc_ops = {
    KRB5_CC_OPS_VERSION,
    "FILE",
    fcc_get_name,
    fcc_resolve,
    fcc_gen_new,
    fcc_initialize,
    fcc_destroy,
    fcc_close,
    fcc_store_cred,
    NULL, /* fcc_retrieve */
    fcc_get_principal,
    fcc_get_first,
    fcc_get_next,
    fcc_end_get,
    fcc_remove_cred,
    fcc_set_flags,
    fcc_get_version,
    fcc_get_cache_first,
    fcc_get_cache_next,
    fcc_end_cache_get,
    fcc_move,
    fcc_get_default_name,
    NULL,
    fcc_lastchange,
    fcc_set_kdc_offset,
    fcc_get_kdc_offset
};