/*
 * Copyright (c) 2013 Larisa Grigore <larisagrigore@gmail.com>.
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Herb Peyerl.
 * 4. The name of Herb Peyerl may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 <unistd.h>

#include "perm.h"
#include <errno.h>

static int
is_root(struct cmsgcred *cred) {
        return (cred->cmcred_euid == 0);
}

static int
is_grpmember(gid_t gid, struct cmsgcred *cred) {
        int n;

        if (cred->cmcred_gid == gid)
                return (1);

        for (n = 0 ; n < cred->cmcred_ngroups ; n++) {
                if (cred->cmcred_groups[n] == gid)
                        return (1);
        }

        return (0);
}

int
ipcperm(struct cmsgcred *cred, struct ipc_perm *perm, int mode) {
        if (cred == NULL)
                return (0);

        if (cred->cmcred_euid != perm->cuid
                        && cred->cmcred_euid != perm->uid) {
                /* In order to modify control info the caller must be
                 * owner, creator or privileged.
                 */
                if (mode & IPC_M)
                        return (is_root(cred) ? 0 : EACCES);

                /* Check for group match. */
                mode >>= 3;
                if (!is_grpmember(perm->gid, cred) &&
                                !is_grpmember(perm->cgid, cred))
                        mode >>= 3;
        }

        if (mode & IPC_M)
                return (0);

        if ((mode & perm->mode) == mode)
                return (0);

        if (is_root(cred))
                return (0);

        return (EACCES);
}