fs.d/autofs/ns_fnmount.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * ns_fnmount.c
 *
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <syslog.h>
#include <rpc/rpc.h>
#include <rpcsvc/nis.h>
#include <xfn/xfn.h>
#include "automount.h"
#include "ns_fnutils.h"


/*
 * The maximum sizes of map names, key names, composite names, and status
 * descriptions, including the trailing '\0'.
 */
#define MAPNAMESZ   (size_t)(AUTOFS_MAXCOMPONENTLEN + 1)
#define KEYNAMESZ   (size_t)(AUTOFS_MAXCOMPONENTLEN + 1)
#define COMPNAMESZ  (size_t)(MAPNAMESZ - FNPREFIXLEN + KEYNAMESZ - 2)
#define DESCSZ      (size_t)512

typedef struct mapent   mapent;
typedef struct mapline  mapline;


/*
 * The name of an attribute.
 */
static const FN_identifier_t attr_exported = {FN_ID_STRING, 8, "exported"};


/*
 * Given a request by a particular user to mount the name "key" under
 * map/context "map", and a set of default mount options, return (in
 * "res") either a list of mapents giving the mounts that need to be
 * performed, or a symbolic link to be created for a user-relative
 * context.  If "shallow" is true return, in place of the list of
 * mapents, a single mapent representing an indirect mount point.
 *
 *  void
 *  getmapent_fn(char *key, char *map, char *opts, uid_t uid,
 *        bool_t shallow, getmapent_fn_res *res);
 */

/*
 * Given a reference, its composite name, default mount options, and a
 * mapent root, return a list of mapents to mount.  If "shallow" is
 * true return, in place of the list of mapents, a single mapent
 * representing an indirect mount point.  The map and key strings are
 * pieces of the composite name such that:
 * "FNPREFIX/cname" == "map/key".
 */
static mapent *
process_ref(const FN_ref_t *ref, const char *cname, char *map, char *key,
    char *opts, char *root, bool_t shallow, FN_status_t *status);

/*
 * Traverse the namespace to find a frontier below ref along which
 * future mounts may need to be triggered.  Add to mapents the
 * corresponding direct autofs mount points.
 *     map: map name for ref
 *     maplen:  strlen(map)
 *     mntpnt:  suffix of map where the current mount request begins
 *      (starts off as "", and grows as we traverse the namespace)
 *     opts:    default mount options
 *     status:  passed from above to avoid having to allocate one on each call
 * Works by calling frontier_aux() on each name bound under ref.
 * Return the new mapents, or free mapents and return NULL on failure.
 */
static mapent *
frontier(mapent *mapents, const FN_ref_t *ref, char *map, size_t maplen,
    char *mntpnt, char *opts, FN_status_t *status);

/*
 * Called by frontier(), once for each "name" that it finds.  map is
 * passed unchanged from frontier().  ref is the reference named by
 * "map/name".  If ref is found to be along the frontier, add the
 * corresponding direct autofs mount point to mapents.  Otherwise
 * continue traversing the namespace to find the frontier.  Other
 * arguments and the return value are as for frontier().
 */
static mapent *
frontier_aux(mapent *mapents, const FN_ref_t *ref, char *map, size_t maplen,
    char *mntpnt, const char *name, char *opts, FN_status_t *status);

/*
 * Given a reference with an address type of ADDR_HOST and its
 * composite name, check the attr_exported attribute to determine if
 * the corresponding directory is exported.  Return FALSE on error.
 */
static bool_t
exported(const FN_ref_t *ref, const char *cname, FN_status_t *status);

/*
 * Find a reference's address type and, if "data" is not NULL, its
 * data string.  If there is no address of a known type, set *typep to
 * NUM_ADDRTYPES; if there are several, stop after finding the first.
 * Return 0 on success.
 */
static int
addr_from_ref(const FN_ref_t *ref, const char *cname, addrtype_t *typep,
    char *data, size_t datasz);

/*
 * Decode an address's data into a string.  Return 0 on success.
 */
static int
str_from_addr(const char *cname, const FN_ref_addr_t *addr, char str[],
    size_t strsz);

/*
 * Given a map name and its current length, append "/name".  Return
 * the new length.  On error, syslog a warning and return 0.
 */
static size_t
append_mapname(char *map, size_t maplen, const char *name);

/*
 * Concatenate two strings using the given separator.  The result is a
 * newly-allocated string, or NULL on error.
 */
static char *
concat(const char *s1, char sep, const char *s2);

/*
 * Add the "nosuid" option to a mapent.  Also check for a sneaky
 * hacker trying to override this option by manually inserting a
 * multiple mount entry into the XFN namespace.  Return FALSE on error.
 */
static bool_t
safe_mapent(mapent *me);

/*
 * Append "nosuid" to a list of options.  The result is a
 * newly-allocated string, or NULL on error.
 */
static char *
safe_opts(const char *opts);

/*
 * Trim comments and trailing whitespace from ml->linebuf, then
 * unquote it and leave the result in ml.  Return 0 on success.
 */
static int
trim_line(mapline *ml);

/*
 * Determine whether ml contains an option string (such as "-ro") and
 * nothing else.
 */
static bool_t
opts_only(const mapline *ml);

/*
 * Allocate a new mapent structure.  The arguments must have been
 * malloc'ed, and are owned by the mapent; they are freed if
 * new_mapent() fails.  If any argument is NULL, the call fails and a
 * memory allocation failure is logged.  A root argument of 'noroot'
 * indicates that the map_root field does not need to be set (it's
 * only needed in the first of a list of mapents).
 */
static char *noroot = "[no root]";
static mapent *
new_mapent(char *root, char *mntpnt, char *fstype, char *mntopts, char *host,
    char *dir);

/*
 * Determine whether cname is a user-relative binding -- such as "myself" --
 * in the initial context.
 */
static bool_t
is_user_relative(const char *cname);

/*
 * Given the name of a user-relative binding, return an equivalent
 * name that is not user-relative.
 */
static char *
equiv_name(FN_ctx_t *, const char *cname, FN_status_t *);

void
getmapent_fn(char *key, char *map, char *opts, uid_t uid, bool_t shallow,
    getmapent_fn_res *res)
{
    size_t          maplen;
    FN_status_t     *status;
    FN_ctx_t        *init_ctx = NULL;
    int         statcode;
    char            cname[COMPNAMESZ];
    FN_composite_name_t *compname;
    FN_ref_t        *ref;
    char            mapname[MAPNAMESZ];
    char            *root;

    res->type = FN_NONE;
    res->m_or_l.mapents = NULL;

    if (init_fn() != 0) {
        return;
    }

    /*
     * For direct mounts, the key is the entire path, and the map
     * name already has the final key component appended.  Split
     * apart the map name and key.  The "root" of the mapent is
     * "/key" for indirect mounts, and "" for direct mounts.
     */
    strcpy(mapname, map);
    if (key[0] == '/') {
        key = strrchr(key, '/') + 1;
        *strrchr(mapname, '/') = '\0';
        root = strdup("");
    } else {
        root = concat("", '/', key);
    }
    map = mapname;
    maplen = strlen(map);

    if ((maplen - FNPREFIXLEN + strlen(key)) >= COMPNAMESZ) {
        if (verbose) {
            syslog(LOG_ERR, "name %s/%s too long", map, key);
        }
        return;
    }
    if (maplen == FNPREFIXLEN) {
        strcpy(cname, key);
    } else {
        sprintf(cname, "%s/%s", map + FNPREFIXLEN + 1, key);
    }

    status = fn_status_create();
    if (status == NULL) {
        if (verbose) {
            syslog(LOG_ERR, "Could not create FNS status object");
        }
        return;
    }
    init_ctx = _fn_ctx_handle_from_initial_with_uid(uid, 0, status);
    if (init_ctx == NULL) {
        logstat(status, "", "No initial context");
        goto done;
    }

#ifndef XFN1ENV
    if (is_user_relative(cname)) {
        res->type = FN_SYMLINK;
        res->m_or_l.symlink = equiv_name(init_ctx, cname, status);
        goto done;
    }
#endif

    if ((compname = new_cname(cname)) == NULL) {
        goto done;
    }
    ref = fn_ctx_lookup(init_ctx, compname, status);
    statcode = fn_status_code(status);
    fn_composite_name_destroy(compname);

    if (trace > 1 && !shallow) {
        trace_prt(1, "  FNS traversal: %s\n", cname);
    }

    if (ref == NULL) {
        if ((statcode != FN_E_NAME_NOT_FOUND) &&
            (statcode != FN_E_NOT_A_CONTEXT)) {
            logstat(status, "lookup failed on", cname);
        }
        goto done;
    }

    res->type = FN_MAPENTS;
    res->m_or_l.mapents =
        process_ref(ref, cname, map, key, opts, root, shallow, status);
    fn_ref_destroy(ref);
done:
    fn_ctx_handle_destroy(init_ctx);
    fn_status_destroy(status);
}


static mapent *
process_ref(const FN_ref_t *ref, const char *cname, char *map, char *key,
    char *opts, char *root, bool_t shallow, FN_status_t *status)
{
    addrtype_t  addrtype;
    mapline     ml;
    char        *addrdata = ml.linebuf;
    mapent      *mapents;
    bool_t      self;
    char        *homedir;
    size_t      maplen;
    char        *colon;
    char        *nfshost;
    char        *nfsdir;

    if ((reftype(ref) < NUM_REFTYPES) &&
        (addr_from_ref(ref, cname, &addrtype, addrdata, LINESZ) == 0)) {

        switch (addrtype) {
        case ADDR_MOUNT:
            if (trim_line(&ml) != 0) {
                return (NULL);
            }
            if (opts_only(&ml)) {
                /* parse_entry() can't handle such lines */
                if (macro_expand("&", ml.linebuf,
                    ml.lineqbuf, LINESZ)) {
                    syslog(LOG_ERR,
                    "%s/%s: opts too long (max %d chars)",
                        FNPREFIX, cname, LINESZ - 1);
                    return (NULL);
                }
                opts = ml.linebuf + 1;  /* skip '-' */
                goto indirect;
            }
            mapents = parse_entry(key, map, opts, &ml, NULL, 0,
                TRUE);
            if (mapents == NULL || !safe_mapent(mapents)) {
                free_mapent(mapents);
                return (NULL);
            }
            free(mapents->map_root);
            mapents->map_root = root;
            break;

        case ADDR_HOST:
            /*
             * Address is of the form "host:dir".
             * If "dir" is not supplied, it defaults to "/".
             */
            colon = strchr(addrdata, ':');
            if (colon == NULL || colon[1] == '\0') {
                nfsdir = strdup("/");
            } else {
                *colon = '\0';
                nfsdir = strdup(colon + 1);
            }
            nfshost = strdup(addrdata);
            /*
             * If nfshost is the local host, the NFS mount
             * request will be converted to a loopback
             * mount.  Otherwise check that the file system
             * is exported.
             */
            if (nfshost != NULL) {
                self = self_check(nfshost);
                if (!self && !exported(ref, cname, status)) {
                    if (transient(status)) {
                        return (NULL);
                    } else {
                        goto indirect;
                    }
                }
            }
            mapents = new_mapent(root, strdup(""), strdup("nfs"),
                safe_opts(opts), nfshost, nfsdir);
            if (self && !shallow) {
                return (mapents);
            }
            break;

        case ADDR_USER:
            homedir = strdup(addrdata);
            homedir[strcspn(homedir, " \t\r\n")] = '\0';
            mapents = new_mapent(root, strdup(""), strdup("lofs"),
                strdup(opts), strdup(""), homedir);
            break;
        }

        if (mapents == NULL) {
            return (NULL);
        }
        if (shallow) {
            mapents->map_root = NULL;   /* don't free "root" */
            free_mapent(mapents);
            goto indirect;
        }

        /* "map" => "map/key" */
        if ((maplen = append_mapname(map, strlen(map), key)) == 0) {
            return (mapents);
        }
        return (frontier(mapents, ref, map, maplen, map + maplen,
            opts, status));
    }

    /* Ref type wasn't recognized. */

indirect:
    /* Install an indirect autofs mount point. */
    return (new_mapent(root, strdup(""), strdup("autofs"), strdup(opts),
        strdup(""), concat(map, '/', key)));
}


/*
 * All that this function really does is call frontier_aux() on every
 * name bound under ref.  The rest is error checking(!)
 *
 * The error handling strategy is to reject the entire mount request
 * (by freeing mapents) if any (potentially) transient error occurs,
 * and to treat nontransient errors as holes in the affected portions
 * of the namespace.
 */
static mapent *
frontier(mapent *mapents, const FN_ref_t *ref, char *map, size_t maplen,
    char *mntpnt, char *opts, FN_status_t *status)
{
    FN_ctx_t        *ctx;
    FN_bindinglist_t    *bindings = NULL;
    FN_ref_t        *child_ref;
    FN_string_t     *child_s;
    const char      *child;
    unsigned int        statcode;

    ctx = fn_ctx_handle_from_ref(ref, XFN2(0) status);
    if (ctx == NULL) {
        if (fn_status_code(status) != FN_E_NO_SUPPORTED_ADDRESS) {
            logstat(status, "from_ref failed for", map);
        }
        goto checkerr_return;
    }

    bindings = fn_ctx_list_bindings(ctx, empty_cname, status);
    fn_ctx_handle_destroy(ctx);
    if (bindings == NULL) {
        logstat(status, "list_bindings failed for", map);
        goto checkerr_return;
    }

    while ((child_s = fn_bindinglist_next(bindings, &child_ref, status))
        != NULL) {
        child = (const char *)fn_string_str(child_s, &statcode);
        if (child == NULL) {
            if (verbose) {
                syslog(LOG_ERR,
                    "FNS string error listing %s", map);
            }
            fn_string_destroy(child_s);
            goto err_return;
        }
        mapents = frontier_aux(mapents, child_ref, map, maplen,
            mntpnt, child, opts, status);
        fn_string_destroy(child_s);
        fn_ref_destroy(child_ref);
        if (mapents == NULL) {
            goto noerr_return;
        }
    }
    if (fn_status_is_success(status)) {
        goto noerr_return;
    } else {
        logstat(status, "error while listing", map);
        /* Fall through to checkerr_return. */
    }

checkerr_return:
    if (!transient(status)) {
        goto noerr_return;
    }
err_return:
    free_mapent(mapents);
    mapents = NULL;
noerr_return:
    fn_bindinglist_destroy(bindings XFN1(status));
    return (mapents);
}


static mapent *
frontier_aux(mapent *mapents, const FN_ref_t *ref, char *map, size_t maplen,
    char *mntpnt, const char *name, char *opts, FN_status_t *status)
{
    addrtype_t  addrtype;
    bool_t      at_frontier;
    mapent      *me;
    size_t      maplen_save = maplen;
    char        *cname = map + FNPREFIXLEN + 1; /* for error msgs */

    if (reftype(ref) >= NUM_REFTYPES) {
        /*
         * We could instead install an indirect autofs mount point
         * here.  That would allow, for example, a user to be bound
         * beneath a file system.
         */
        return (mapents);
    }

    /* "map" => "map/name" */
    if ((maplen = append_mapname(map, maplen, name)) == 0) {
        return (mapents);
    }
    if (trace > 1) {
        trace_prt(1, "  FNS traversal: %s/\n", cname);
    }

    /*
     * If this is an address type that we know how to mount, then
     * we have reached the frontier.
     */
    at_frontier = (addr_from_ref(ref, cname, &addrtype, NULL, 0) == 0);
    /*
     * For an ADDR_HOST address, treat a non-exported directory as
     * if the address type were not known:  continue searching for
     * exported subdirectories.
     */
    if (at_frontier && (addrtype == ADDR_HOST)) {
        if (!exported(ref, cname, status)) {
            if (transient(status)) {
                free_mapent(mapents);
                return (NULL);
            } else {
                at_frontier = FALSE;
            }
        }
    }
    /*
     * If we have reached the frontier, install a direct autofs
     * mount point (which will trigger the actual mount if the
     * user steps on it later).  Otherwise, continue traversing
     * the namespace looking for known address types.
     */
    if (at_frontier) {
        opts = (opts[0] != '\0')
            ? concat(opts, ',', "direct")
            : strdup("direct");
        me = new_mapent(noroot, strdup(mntpnt), strdup("autofs"), opts,
            strdup(""), strdup(map));
        if (me != NULL) {
            /* Link new mapent into list (not at the head). */
            me->map_next = mapents->map_next;
            mapents->map_next = me;
        } else {
            free_mapent(mapents);
            mapents = NULL;
        }
    } else {
        mapents =
            frontier(mapents, ref, map, maplen, mntpnt, opts, status);
    }
    map[maplen_save] = '\0';    /* "map/name" => "map" */
    return (mapents);
}


static bool_t
exported(const FN_ref_t *ref, const char *cname, FN_status_t *status)
{
    FN_ctx_t        *ctx;
    FN_attribute_t      *attr;

    ctx = fn_ctx_handle_from_ref(ref, XFN2(0) status);
    if (ctx == NULL) {
        logstat(status, "from_ref failed for", cname);
        return (FALSE);
    }
    attr = fn_attr_get(ctx, empty_cname, &attr_exported, XFN2(1) status);
    fn_ctx_handle_destroy(ctx);

    switch (fn_status_code(status)) {
    case FN_SUCCESS:
        fn_attribute_destroy(attr);
        break;
    case FN_E_NO_SUCH_ATTRIBUTE:
        break;
    default:
        logstat(status, "could not get attributes for", cname);
    }
    return (attr != NULL);
}


static int
addr_from_ref(const FN_ref_t *ref, const char *cname, addrtype_t *typep,
    char *data, size_t datasz)
{
    const FN_ref_addr_t *addr;
    void            *iter_pos;

    addr = fn_ref_first(ref, &iter_pos);
    if (addr == NULL) {
        if (verbose) {
            syslog(LOG_ERR, "FNS ref with no address: %s", cname);
        }
        return (-1);
    }
    while (addr != NULL) {
        *typep = addrtype(addr);
        if (*typep < NUM_ADDRTYPES) {
            return ((data != NULL)
                ? str_from_addr(cname, addr, data, datasz)
                : 0);
        }
        addr = fn_ref_next(ref, &iter_pos);
    }
    return (-1);
}


static int
str_from_addr(const char *cname, const FN_ref_addr_t *addr, char str[],
    size_t strsz)
{
    XDR xdr;
    int res;

    xdrmem_create(&xdr, (caddr_t)fn_ref_addr_data(addr),
        fn_ref_addr_length(addr), XDR_DECODE);
    if (!xdr_string(&xdr, &str, strsz)) {
        if (verbose) {
            syslog(LOG_ERR,
                "Could not decode FNS address for %s", cname);
        }
        res = -1;
    } else {
        res = 0;
    }
    xdr_destroy(&xdr);
    return (res);
}

static size_t
append_mapname(char *map, size_t maplen, const char *name)
{
    size_t namelen = strlen(name);

    if (maplen + 1 + namelen >= MAPNAMESZ) {
        if (verbose) {
            syslog(LOG_ERR, "FNS name %s/%s too long",
                map + FNPREFIXLEN + 1, name);
        }
        return (0);
    }
    sprintf(map + maplen, "/%s", name);
    return (maplen + 1 + namelen);
}


static char *
concat(const char *s1, char sep, const char *s2)
{
    char *s = malloc(strlen(s1) + 1 + strlen(s2) + 1);

    if (s != NULL) {
        sprintf(s, "%s%c%s", s1, sep, s2);
    }
    return (s);
}


static bool_t
safe_mapent(mapent *me)
{
    char    *opts;

    if (me->map_next != NULL) {
        /* Multiple mounts don't belong in XFN namespace. */
        return (NULL);
    }
    opts = me->map_mntopts;
    me->map_mntopts = safe_opts(opts);
    free(opts);
    return (me->map_mntopts != NULL);
}


static char *
safe_opts(const char *opts)
{
    char    *start;
    size_t  len;

    if (opts[0] == '\0') {
        return (strdup(MNTOPT_NOSUID));
    }

    /* A quick-and-dirty check to see if "nosuid" is already there. */
    start = strstr(opts, MNTOPT_NOSUID);
    len = sizeof (MNTOPT_NOSUID) - 1;   /* "-1" for trailing '\0' */
    if (start != NULL) {
        while (start > opts && isspace(*(start - 1))) {
            start--;
        }
        if ((start == opts || *(start - 1) == ',') &&
            opts[len] == ',' || opts[len] == '\0') {
            return (strdup(opts));
        }
    }
    return (concat(opts, ',', MNTOPT_NOSUID));
}


static int
trim_line(mapline *ml)
{
    char    *end;   /* pointer to '\0' at end of linebuf */

    end = ml->linebuf + strcspn(ml->linebuf, "#");
    while ((end > ml->linebuf) && isspace(end[-1])) {
        end--;
    }
    if (end <= ml->linebuf) {
        return (-1);
    }
    *end = '\0';
    unquote(ml->linebuf, ml->lineqbuf);
    return (0);
}


static bool_t
opts_only(const mapline *ml)
{
    const char *s = ml->linebuf;
    const char *q = ml->lineqbuf;

    if (*s != '-') {
        return (FALSE);
    }
    for (; *s != '\0'; s++, q++) {
        if (isspace(*s) && (*q == ' ')) {
            return (FALSE);
        }
    }
    return (TRUE);
}


static mapent *
new_mapent(char *root, char *mntpnt, char *fstype, char *mntopts, char *host,
    char *dir)
{
    mapent      *me;
    struct mapfs    *mfs;
    char        *mounter = NULL;

    me = calloc(1, sizeof (*me));
    mfs = calloc(1, sizeof (*mfs));
    if (fstype != NULL) {
        mounter = strdup(fstype);
    }
    if ((mntpnt == NULL) || (fstype == NULL) || (mntopts == NULL) ||
        (host == NULL) || (dir == NULL) || (me == NULL) || (mfs == NULL) ||
        (mounter == NULL) || (root == NULL)) {
        log_mem_failure();
        free(me);
        free(mfs);
        free(mounter);
        free(root);
        free(mntpnt);
        free(fstype);
        free(mntopts);
        free(host);
        free(dir);
        return (NULL);
    }
    me->map_root    = (root != noroot) ? root : NULL;
    me->map_fstype  = fstype;
    me->map_mounter = mounter;
    me->map_mntpnt  = mntpnt;
    me->map_mntopts = mntopts;
    me->map_fsw = NULL;
    me->map_fswq    = NULL;
    me->map_fs  = mfs;
    mfs->mfs_host   = host;
    mfs->mfs_dir    = dir;
    me->map_mntlevel = -1;
    me->map_modified = FALSE;
    me->map_faked = FALSE;
    me->map_err = 0;        /* MAPENT_NOERR */
    return (me);
}


#ifndef XFN1ENV

/*
 * User-relative bindings in the initial context, and the leading components
 * of their non-user-relative equivalents.  Leading components are listed in
 * the order in which they should be tried.  Each list is NULL-terminated
 * (the compiler generously does this for us).
 * For "myorgunit", for example, we first check if it is equivalent to
 * "thisorgunit".  If not, we translate it into "org/<something>".
 */
#define MAX_LEADS 3

static struct {
    const char  *binding;
    const char  *leads[MAX_LEADS + 1];
} user_rel[] = {
    {"thisuser",    {"user", "thisorgunit", "org"}},
    {"myself",  {"user", "thisorgunit", "org"}},
    {"_myself", {"_user", "_thisorgunit", "_orgunit"}},
    {"myorgunit",   {"thisorgunit", "org"}},
    {"_myorgunit",  {"_thisorgunit", "_orgunit"}},
    {"myens",   {"thisens"}},
    {"_myens",  {"_thisens"}}
};


static bool_t
is_user_relative(const char *cname)
{
    int i;

    for (i = 0; i < sizeof (user_rel) / sizeof (user_rel[0]); i++) {
        if (strcmp(cname, user_rel[i].binding) == 0) {
            return (TRUE);
        }
    }
    return (FALSE);
}


static char *
equiv_name(FN_ctx_t *ctx, const char *cname, FN_status_t *status)
{
    FN_composite_name_t *name;
    FN_string_t     *leading_name;
    FN_composite_name_t *equiv;
    FN_string_t     *equiv_string;
    const char      *equiv_str;
    char            *equiv_str_dup;
    const char      **leads;
    unsigned int        stat;
    int         i;

    for (i = 0; i < sizeof (user_rel) / sizeof (user_rel[0]); i++) {
        if (strcmp(cname, user_rel[i].binding) == 0) {
            break;
        }
    }
    if ((name = new_cname(cname)) == NULL) {
        return (NULL);
    }
    leads = user_rel[i].leads;  /* array of leading names to try */
    do {
        leading_name = fn_string_from_str((unsigned char *)*leads);
        if (leading_name == NULL) {
            log_mem_failure();
            fn_composite_name_destroy(name);
            return (NULL);
        }
        equiv = prelim_fn_ctx_equivalent_name(ctx, name, leading_name,
            status);
        fn_string_destroy(leading_name);
    } while (equiv == NULL && *++leads != NULL);

    fn_composite_name_destroy(name);

    if (equiv == NULL) {
        if (transient(status)) {
            logstat(status, "could not find equivalent of", cname);
        }
        return (NULL);
    }
    equiv_string = fn_string_from_composite_name(equiv, &stat);
    fn_composite_name_destroy(equiv);
    if (equiv_string == NULL) {
        log_mem_failure();
        return (NULL);
    }
    equiv_str = (const char *)fn_string_str(equiv_string, &stat);
    if (equiv_str == NULL ||
        (equiv_str_dup = strdup(equiv_str)) == NULL) {
        log_mem_failure();
        fn_string_destroy(equiv_string);
        return (NULL);
    }
    fn_string_destroy(equiv_string);
    return (equiv_str_dup);
}

#endif  /* XFN1ENV */