util.c

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/*
 * util.c       Various utility functions.
 *
 * Version:     $Id: 7f5c2d4a90910e9bc2e5593729b491d3676283c3 $
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 *
 
 */
 
RCSID("$Id: 7f5c2d4a90910e9bc2e5593729b491d3676283c3 $")
 
#include <freeradius-devel/server/base.h>
 
#include <freeradius-devel/util/base16.h>
#include <freeradius-devel/util/perm.h>
 
 
#include <fcntl.h>
 
static bool suid_down_permanent = false;        //!< Record whether we've permanently dropped privilledges
 
/*
 *      The signal() function in Solaris 2.5.1 sets SA_NODEFER in
 *      sa_flags, which causes grief if signal() is called in the
 *      handler before the cause of the signal has been cleared.
 *      (Infinite recursion).
 *
 *      The same problem appears on HPUX, so we avoid it, if we can.
 *
 *      Using sigaction() to reset the signal handler fixes the problem,
 *      so where available, we prefer that solution.
 */
 
void (*reset_signal(int signo, void (*func)(int)))(int)
{
#ifdef HAVE_SIGACTION
        struct sigaction act, oact;
 
        memset(&act, 0, sizeof(act));
        act.sa_handler = func;
        sigemptyset(&act.sa_mask);
        act.sa_flags = 0;
#ifdef  SA_INTERRUPT            /* SunOS */
        act.sa_flags |= SA_INTERRUPT;
#endif
        if (sigaction(signo, &act, &oact) < 0)
                return SIG_ERR;
        return oact.sa_handler;
#else
 
        /*
         *      re-set by calling the 'signal' function, which
         *      may cause infinite recursion and core dumps due to
         *      stack growth.
         *
         *      However, the system is too dumb to implement sigaction(),
         *      so we don't have a choice.
         */
        signal(signo, func);
 
        return NULL;
#endif
}
 
/** Ensures that a filename cannot walk up the directory structure
 *
 * Also sanitizes control chars.
 *
 * @param request Current request (may be NULL).
 * @param out Output buffer.
 * @param outlen Size of the output buffer.
 * @param in string to escape.
 * @param arg Context arguments (unused, should be NULL).
 */
ssize_t rad_filename_make_safe(UNUSED request_t *request, char *out, size_t outlen, char const *in, UNUSED void *arg)
{
        char const *q = in;
        char *p = out;
        size_t left = outlen;
 
        while (*q) {
                if (*q != '/') {
                        if (left < 2) break;
 
                        /*
                         *      Smash control characters and spaces to
                         *      something simpler.
                         */
                        if (*q < ' ') {
                                *(p++) = '_';
                                q++;
                                continue;
                        }
 
                        *(p++) = *(q++);
                        left--;
                        continue;
                }
 
                /*
                 *      For now, allow slashes in the expanded
                 *      filename.  This allows the admin to set
                 *      attributes which create sub-directories.
                 *      Unfortunately, it also allows users to send
                 *      attributes which *may* end up creating
                 *      sub-directories.
                 */
                if (left < 2) break;
                *(p++) = *(q++);
 
                /*
                 *      Get rid of ////../.././///.///..//
                 */
        redo:
                /*
                 *      Get rid of ////
                 */
                if (*q == '/') {
                        q++;
                        goto redo;
                }
 
                /*
                 *      Get rid of /./././
                 */
                if ((q[0] == '.') &&
                    (q[1] == '/')) {
                        q += 2;
                        goto redo;
                }
 
                /*
                 *      Get rid of /../../../
                 */
                if ((q[0] == '.') && (q[1] == '.') &&
                    (q[2] == '/')) {
                        q += 3;
                        goto redo;
                }
        }
        *p = '\0';
 
        return (p - out);
}
 
int rad_filename_box_make_safe(fr_value_box_t *vb, UNUSED void *uxtc)
{
        char                    *escaped;
        size_t                  len;
 
        if (vb->vb_length == 0) return 0;
 
        fr_assert(!fr_value_box_is_safe_for(vb, rad_filename_box_make_safe));
 
        /*
         *      Allocate an output buffer, only ever the same or shorter than the input
         */
        MEM(escaped = talloc_array(vb, char, vb->vb_length + 1));
 
        len = rad_filename_make_safe(NULL, escaped, (vb->vb_length + 1), vb->vb_strvalue, NULL);
 
        fr_value_box_strdup_shallow_replace(vb, escaped, len);
 
        return 0;
}
 
/** Escapes the raw string such that it should be safe to use as part of a file path
 *
 * This function is designed to produce a string that's still readable but portable
 * across the majority of file systems.
 *
 * For security reasons it cannot remove characters from the name, and must not allow
 * collisions to occur between different strings.
 *
 * With that in mind '-' has been chosen as the escape character, and will be double
 * escaped '-' -> '--' to avoid collisions.
 *
 * Escaping should be reversible if the original string needs to be extracted.
 *
 * @note function takes additional arguments so that it may be used as an xlat escape
 *      function but it's fine to call it directly.
 *
 * @note OSX/Unix/NTFS/VFAT have a max filename size of 255 bytes.
 *
 * @param request Current request (may be NULL).
 * @param out Output buffer.
 * @param outlen Size of the output buffer.
 * @param in string to escape.
 * @param arg Context arguments (unused, should be NULL).
 */
ssize_t rad_filename_escape(UNUSED request_t *request, char *out, size_t outlen, char const *in, UNUSED void *arg)
{
        size_t freespace = outlen;
 
        while (*in != '\0') {
                size_t utf8_len;
 
                /*
                 *      Encode multibyte UTF8 chars
                 */
                utf8_len = fr_utf8_char((uint8_t const *) in, -1);
                if (utf8_len > 1) {
                        if (freespace <= (utf8_len * 3)) break;
 
                        switch (utf8_len) {
                        case 2:
                                snprintf(out, freespace, "-%x-%x", (uint8_t)in[0], (uint8_t)in[1]);
                                break;
 
                        case 3:
                                snprintf(out, freespace, "-%x-%x-%x", (uint8_t)in[0], (uint8_t)in[1], (uint8_t)in[2]);
                                break;
 
                        case 4:
                                snprintf(out, freespace, "-%x-%x-%x-%x", (uint8_t)in[0], (uint8_t)in[1], (uint8_t)in[2], (uint8_t)in[3]);
                                break;
                        }
 
                        freespace -= (utf8_len * 3);
                        out += (utf8_len * 3);
                        in += utf8_len;
 
                        continue;
                }
 
                /*
                 *      Safe chars
                 */
                if (((*in >= 'A') && (*in <= 'Z')) ||
                    ((*in >= 'a') && (*in <= 'z')) ||
                    ((*in >= '0') && (*in <= '9')) ||
                    (*in == '_')) {
                        if (freespace <= 1) break;
 
                        *out++ = *in++;
                        freespace--;
                        continue;
                }
                if (freespace <= 2) break;
 
                /*
                 *      Double escape '-' (like \\‍)
                 */
                if (*in == '-') {
                        *out++ = '-';
                        *out++ = '-';
 
                        freespace -= 2;
                        in++;
                        continue;
                }
 
                /*
                 *      Unsafe chars
                 */
                *out++ = '-';
                fr_base16_encode(&FR_SBUFF_OUT(out, freespace), &FR_DBUFF_TMP((uint8_t const *)in, 1));
                in++;
                out += 2;
                freespace -= 3;
        }
        *out = '\0';
 
        return outlen - freespace;
}
 
int rad_filename_box_escape(fr_value_box_t *vb, UNUSED void *uxtc)
{
        char                    *escaped;
        size_t                  len;
 
        if (vb->vb_length == 0) return 0;
 
        fr_assert(!fr_value_box_is_safe_for(vb, rad_filename_box_escape));
 
        /*
         *      Allocate an output buffer, if every character is escaped,
         *      it will be 3 times the input
         */
        MEM(escaped = talloc_array(vb, char, vb->vb_length * 3 + 1));
 
        len = rad_filename_escape(NULL, escaped, (vb->vb_length * 3 + 1), vb->vb_strvalue, NULL);
 
        /*
         *      If the escaped length == input length, no changes were done.
         */
        if (len == vb->vb_length) {
                talloc_free(escaped);
                return 0;
        }
 
        fr_value_box_strdup_shallow_replace(vb, escaped, len);
 
        return 0;
}
 
/** Converts data stored in a file name back to its original form
 *
 * @param out Where to write the unescaped string (may be the same as in).
 * @param outlen Length of the output buffer.
 * @param in Input filename.
 * @param inlen Length of input.
 * @return
 *      - Number of bytes written to output buffer
 *      - offset where parse error occurred on failure.
 */
ssize_t rad_filename_unescape(char *out, size_t outlen, char const *in, size_t inlen)
{
        char const *p, *end = in + inlen;
        size_t freespace = outlen;
 
        for (p = in; p < end; p++) {
                if (freespace <= 1) break;
 
                if (((*p >= 'A') && (*p <= 'Z')) ||
                    ((*p >= 'a') && (*p <= 'z')) ||
                    ((*p >= '0') && (*p <= '9')) ||
                    (*p == '_')) {
                        *out++ = *p;
                        freespace--;
                        continue;
                }
 
                if (p[0] == '-') {
                        /*
                         *      End of input, '-' needs at least one extra char after
                         *      it to be valid.
                         */
                        if ((end - p) < 2) return in - p;
                        if (p[1] == '-') {
                                p++;
                                *out++ = '-';
                                freespace--;
                                continue;
                        }
 
                        /*
                         *      End of input, '-' must be followed by <hex><hex>
                         *      but there aren't enough chars left
                         */
                        if ((end - p) < 3) return in - p;
 
                        /*
                         *      If hex2bin returns 0 the next two chars weren't hexits.
                         */
                        if (fr_base16_decode(NULL,
                                       &FR_DBUFF_TMP((uint8_t *) out, 1),
                                       &FR_SBUFF_IN(in, 1), false) == 0) return in - (p + 1);
                        in += 2;
                        out++;
                        freespace--;
                }
 
                return in - p; /* offset we found the bad char at */
        }
        *out = '\0';
 
        return outlen - freespace;      /* how many bytes were written */
}
 
/** talloc a buffer to hold the concatenated value of all elements of argv
 *
 * @param ctx to allocate buffer in.
 * @param argv array of substrings.
 * @param argc length of array.
 * @param c separation character. Optional, may be '\0' for no separator.
 * @return the concatenation of the elements of argv, separated by c.
 */
char *rad_ajoin(TALLOC_CTX *ctx, char const **argv, int argc, char c)
{
        char *buff, *p;
        int i;
        size_t total = 0, freespace;
 
        if (!*argv) {
                goto null;
        }
 
        for (i = 0; i < argc; i++) total += (strlen(argv[i]) + ((c == '\0') ? 0 : 1));
        if (!total) {
        null:
                return talloc_zero_array(ctx, char, 1);
        }
 
        if (c == '\0') total++;
 
        freespace = total;
        buff = p = talloc_array(ctx, char, total);
        for (i = 0; i < argc; i++) {
                size_t len;
 
                len = strlcpy(p, argv[i], freespace);
                p += len;
                freespace -= len;
 
                *p++ = c;
                freespace--;
        }
        buff[total] = '\0';
 
        return buff;
}
 
/*
 *      Copy a quoted string.
 */
static int rad_copy_string(char *to, char const *from)
{
        int length = 0;
        char quote = *from;
 
        do {
                if (*from == '\\') {
                        *(to++) = *(from++);
                        length++;
                }
                *(to++) = *(from++);
                length++;
        } while (*from && (*from != quote));
 
        if (*from != quote) return -1; /* not properly quoted */
 
        *(to++) = quote;
        length++;
        *to = '\0';
 
        return length;
}
 
/*
 *      Copy a quoted string but without the quotes. The length
 *      returned is the number of chars written; the number of
 *      characters consumed is 2 more than this.
 */
static int rad_copy_string_bare(char *to, char const *from)
{
        int length = 0;
        char quote = *from;
 
        from++;
        while (*from && (*from != quote)) {
                if (*from == '\\') {
                        *(to++) = *(from++);
                        length++;
                }
                *(to++) = *(from++);
                length++;
        }
 
        if (*from != quote) return -1; /* not properly quoted */
 
        *to = '\0';
 
        return length;
}
 
 
/*
 *      Copy a %{} string.
 */
static int rad_copy_variable(char *to, char const *from)
{
        int length = 0;
        int sublen;
 
        *(to++) = *(from++);
        length++;
 
        while (*from) {
                switch (*from) {
                case '"':
                case '\'':
                        sublen = rad_copy_string(to, from);
                        if (sublen < 0) return sublen;
                        from += sublen;
                        to += sublen;
                        length += sublen;
                        break;
 
                case '}':       /* end of variable expansion */
                        *(to++) = *(from++);
                        *to = '\0';
                        length++;
                        return length; /* proper end of variable */
 
                case '\\':
                        *(to++) = *(from++);
                        *(to++) = *(from++);
                        length += 2;
                        break;
 
                case '%':       /* start of variable expansion */
                        if (from[1] == '{') {
                                *(to++) = *(from++);
                                length++;
 
                                sublen = rad_copy_variable(to, from);
                                if (sublen < 0) return sublen;
                                from += sublen;
                                to += sublen;
                                length += sublen;
                                break;
                        } /* else FIXME: catch %%{ ?*/
 
                        FALL_THROUGH;
                default:
                        *(to++) = *(from++);
                        length++;
                        break;
                }
        } /* loop over the input string */
 
        /*
         *      We ended the string before a trailing '}'
         */
 
        return -1;
}
 
uint32_t rad_pps(uint32_t *past, uint32_t *present, time_t *then, struct timeval *now)
{
        uint32_t pps;
 
        if (*then != now->tv_sec) {
                *then = now->tv_sec;
                *past = *present;
                *present = 0;
        }
 
        /*
         *      Bootstrap PPS by looking at a percentage of
         *      the previous PPS.  This lets us take a moving
         *      count, without doing a moving average.  If
         *      we're a fraction "f" (0..1) into the current
         *      second, we can get a good guess for PPS by
         *      doing:
         *
         *      PPS = pps_now + pps_old * (1 - f)
         *
         *      It's an instantaneous measurement, rather than
         *      a moving average.  This will hopefully let it
         *      respond better to sudden spikes.
         *
         *      Doing the calculations by thousands allows us
         *      to not overflow 2^32, AND to not underflow
         *      when we divide by USEC.
         */
        pps = USEC - now->tv_usec; /* useconds left in previous second */
        pps /= 1000;               /* scale to milliseconds */
        pps *= *past;              /* multiply by past count to get fraction */
        pps /= 1000;               /* scale to usec again */
        pps += *present;           /* add in current count */
 
        return pps;
}
 
/** Split string into words and expand each one
 *
 * @param request Current request.
 * @param cmd string to split.
 * @param max_argc the maximum number of arguments to split into.
 * @param argv Where to write the pointers into argv_buf.
 * @param can_fail If false, stop processing if any of the xlat expansions fail.
 * @param argv_buflen size of argv_buf.
 * @param argv_buf temporary buffer we used to mangle/expand cmd.
 *      Pointers to offsets of this buffer will be written to argv.
 * @return argc or -1 on failure.
 */
 
int rad_expand_xlat(request_t *request, char const *cmd,
                    int max_argc, char const *argv[], bool can_fail,
                    size_t argv_buflen, char *argv_buf)
{
        char const *from;
        char *to;
        int argc = -1;
        int i;
        int left;
 
        if (strlen(cmd) > (argv_buflen - 1)) {
                fr_strerror_const("Expansion string is too long for output buffer");
                return -1;
        }
 
        /*
         *      Check for bad escapes.
         */
        if (cmd[strlen(cmd) - 1] == '\\') {
                fr_strerror_const("Expansion string ends with a trailing backslash - invalid escape sequence");
                return -1;
        }
 
        strlcpy(argv_buf, cmd, argv_buflen);
 
        /*
         *      Split the string into argv's BEFORE doing xlat_eval...
         */
        from = cmd;
        to = argv_buf;
        argc = 0;
        while (*from) {
                int length;
 
                fr_skip_whitespace(from);
 
                argv[argc] = to;
                argc++;
 
                if (argc >= (max_argc - 1)) break;
 
                /*
                 *      Copy the argv over to our buffer.
                 */
                while (*from && (*from != ' ') && (*from != '\t')) {
                        if (to >= argv_buf + argv_buflen - 1) {
                                fr_strerror_const("Expansion string is too long for output buffer");
                                return -1;
                        }
 
                        switch (*from) {
                        case '"':
                        case '\'':
                                length = rad_copy_string_bare(to, from);
                                if (length < 0) {
                                        fr_strerror_const("Invalid quoted string in expansion");
                                        return -1;
                                }
                                from += length+2;
                                to += length;
                                break;
 
                        case '%':
                                if (from[1] == '{') {
                                        *(to++) = *(from++);
 
                                        length = rad_copy_variable(to, from);
                                        if (length < 0) {
                                                fr_strerror_const("Invalid variable in expansion");
                                                return -1;
                                        }
                                        from += length;
                                        to += length;
                                } else { /* FIXME: catch %%{ ? */
                                        *(to++) = *(from++);
                                }
                                break;
 
                        case '\\':
                                if (from[1] == ' ') from++;
                                FALL_THROUGH;
 
                        default:
                                *(to++) = *(from++);
                        }
                } /* end of string, or found a space */
 
                *(to++) = '\0'; /* terminate the string */
        }
 
        /*
         *      We have to have SOMETHING, at least.
         */
        if (argc <= 0) {
                fr_strerror_const("Expansion string is empty");
                return -1;
        }
 
        /*
         *      Expand each string, as appropriate.
         */
        left = argv_buf + argv_buflen - to;
        for (i = 0; i < argc; i++) {
                int sublen;
 
                /*
                 *      Don't touch argv's which won't be translated.
                 */
                if (strchr(argv[i], '%') == NULL) continue;
 
                if (!request) continue;
 
                sublen = xlat_eval(to, left - 1, request, argv[i], NULL, NULL);
                if (sublen <= 0) {
                        if (can_fail) {
                                /*
                                 *      Fail to be backwards compatible.
                                 *
                                 *      It's yucky, but it won't break anything,
                                 *      and it won't cause security problems.
                                 */
                                sublen = 0;
                        } else {
                                fr_strerror_const("Failed expanding substring");
                                return -1;
                        }
                }
 
                argv[i] = to;
                to += sublen;
                *(to++) = '\0';
                left -= sublen;
                left--;
 
                if (left <= 0) {
                        fr_strerror_const("Ran out of space while expanding arguments");
                        return -1;
                }
        }
        argv[argc] = NULL;
 
        return argc;
}
 
#ifdef HAVE_SETUID
static bool doing_setuid = false;
static uid_t suid_down_uid = (uid_t)-1;
 
/** Set the uid and gid used when dropping privileges
 *
 * @note if this function hasn't been called, rad_suid_down will have no effect.
 *
 * @param uid to drop down to.
 */
void rad_suid_set_down_uid(uid_t uid)
{
        suid_down_uid = uid;
        doing_setuid = true;
}
 
#  if defined(HAVE_SETRESUID) && defined (HAVE_GETRESUID)
void rad_suid_up(void)
{
        uid_t ruid, euid, suid;
 
        if (getresuid(&ruid, &euid, &suid) < 0) {
                ERROR("Failed getting saved UID's");
                fr_exit_now(EXIT_FAILURE);
        }
 
        if (setresuid(-1, suid, -1) < 0) {
                ERROR("Failed switching to privileged user");
                fr_exit_now(EXIT_FAILURE);
        }
 
        if (geteuid() != suid) {
                ERROR("Switched to unknown UID");
                fr_exit_now(EXIT_FAILURE);
        }
}
 
void rad_suid_down(void)
{
        if (!doing_setuid) return;
 
        if (setresuid(-1, suid_down_uid, geteuid()) < 0) {
                struct passwd *passwd;
                char const *name;
 
                name = (fr_perm_getpwuid(NULL, &passwd, suid_down_uid) < 0) ? "unknown" : passwd->pw_name;
                ERROR("Failed switching to uid %s: %s", name, fr_syserror(errno));
                talloc_free(passwd);
                fr_exit_now(EXIT_FAILURE);
        }
 
        if (geteuid() != suid_down_uid) {
                ERROR("Failed switching uid: UID is incorrect");
                fr_exit_now(EXIT_FAILURE);
        }
 
        fr_reset_dumpable();
}
 
void rad_suid_down_permanent(void)
{
        if (!doing_setuid) return;
 
        if (setresuid(suid_down_uid, suid_down_uid, suid_down_uid) < 0) {
                struct passwd *passwd;
                char const *name;
 
                name = (fr_perm_getpwuid(NULL, &passwd, suid_down_uid) < 0) ? "unknown" : passwd->pw_name;
                ERROR("Failed in permanent switch to uid %s: %s", name, fr_syserror(errno));
                talloc_free(passwd);
                fr_exit_now(EXIT_FAILURE);
        }
 
        if (geteuid() != suid_down_uid) {
                ERROR("Switched to unknown uid");
                fr_exit_now(EXIT_FAILURE);
        }
 
        fr_reset_dumpable();
 
        suid_down_permanent = true;
}
#  else
/*
 *      Much less secure...
 */
void rad_suid_up(void)
{
        if (!doing_setuid) return;
 
        if (seteuid(0) < 0) {
                ERROR("Failed switching up to euid 0: %s", fr_syserror(errno));
                fr_exit_now(EXIT_FAILURE);
        }
 
}
 
void rad_suid_down(void)
{
        if (!doing_setuid) return;
 
        if (geteuid() == suid_down_uid) return;
 
        if (seteuid(suid_down_uid) < 0) {
                struct passwd *passwd;
                char const *name;
 
                name = (fr_perm_getpwuid(NULL, &passwd, suid_down_uid) < 0) ? "unknown": passwd->pw_name;
                ERROR("Failed switching to euid %s: %s", name, fr_syserror(errno));
                talloc_free(passwd);
                fr_exit_now(EXIT_FAILURE);
        }
 
        fr_reset_dumpable();
}
 
void rad_suid_down_permanent(void)
{
        if (!doing_setuid) return;
 
        /*
         *      Already done.  Don't do anything else.
         */
        if (getuid() == suid_down_uid) return;
 
        /*
         *      We're root, but running as a normal user.  Fix that,
         *      so we can call setuid().
         */
        if (geteuid() == suid_down_uid) {
                rad_suid_up();
        }
 
        if (setuid(suid_down_uid) < 0) {
                struct passwd *passwd;
                char const *name;
 
                name = (fr_perm_getpwuid(NULL, &passwd, suid_down_uid) < 0) ? "unknown": passwd->pw_name;
                ERROR("Failed switching permanently to uid %s: %s", name, fr_syserror(errno));
                talloc_free(passwd);
                fr_exit_now(EXIT_FAILURE);
        }
 
        fr_reset_dumpable();
 
        suid_down_permanent = true;
}
#  endif /* HAVE_SETRESUID && HAVE_GETRESUID */
#else  /* HAVE_SETUID */
void rad_suid_set_down_uid(uid_t uid)
{
}
 
void rad_suid_up(void)
{
}
 
void rad_suid_down(void)
{
        fr_reset_dumpable();
}
 
void rad_suid_down_permanent(void)
{
        fr_reset_dumpable();
}
#endif /* HAVE_SETUID */
 
/** Return whether we've permanently dropped root privileges
 *
 * @return
 *      - true if root privileges have been dropped.
 *      - false if root privileges have not been dropped.
 */
bool rad_suid_is_down_permanent(void)
{
        return suid_down_permanent;
}
 
/** Alter the effective user id
 *
 * @param uid to set
 * @return
 *      - 0 on success.
 *      - -1 on failure.
 */
int rad_seuid(uid_t uid)
{
        if (seteuid(uid) < 0) {
                int sete_errno = errno; /* errno sets overwritten by fr_perm_getpwuid */
                struct passwd *passwd;
 
                if (fr_perm_getpwuid(NULL, &passwd, uid) < 0) return -1;
                fr_strerror_printf("%s", fr_syserror(sete_errno));
                talloc_free(passwd);
 
                return -1;
        }
        return 0;
}
 
/** Alter the effective user id
 *
 * @param gid to set
 * @return
 *      - 0 on success.
 *      - -1 on failure.
 */
int rad_segid(gid_t gid)
{
        if (setegid(gid) < 0) {
                int sete_errno = errno; /* errno sets overwritten by fr_perm_getgrgid */
                struct group *group;
 
                if (fr_perm_getgrgid(NULL, &group, gid) < 0) return -1;
                fr_strerror_printf("%s", fr_syserror(sete_errno));
                talloc_free(group);
 
                return -1;
        }
        return 0;
}