// SPDX-License-Identifier: GPL-2.0-or-later
/* Key permission checking
 *
 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/export.h>
#include <linux/security.h>
#include "internal.h"

/**
 * key_task_permission - Check a key can be used
 * @key_ref: The key to check.
 * @cred: The credentials to use.
 * @need_perm: The permission required.
 *
 * Check to see whether permission is granted to use a key in the desired way,
 * but permit the security modules to override.
 *
 * The caller must hold either a ref on cred or must hold the RCU readlock.
 *
 * Returns 0 if successful, -EACCES if access is denied based on the
 * permissions bits or the LSM check.
 */
int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
                        enum key_need_perm need_perm)
{
        struct key *key;
        key_perm_t kperm, mask;
        int ret;

        switch (need_perm) {
        default:
                WARN_ON(1);
                return -EACCES;
        case KEY_NEED_UNLINK:
        case KEY_SYSADMIN_OVERRIDE:
        case KEY_AUTHTOKEN_OVERRIDE:
        case KEY_DEFER_PERM_CHECK:
                goto lsm;

        case KEY_NEED_VIEW:     mask = KEY_OTH_VIEW;    break;
        case KEY_NEED_READ:     mask = KEY_OTH_READ;    break;
        case KEY_NEED_WRITE:    mask = KEY_OTH_WRITE;   break;
        case KEY_NEED_SEARCH:   mask = KEY_OTH_SEARCH;  break;
        case KEY_NEED_LINK:     mask = KEY_OTH_LINK;    break;
        case KEY_NEED_SETATTR:  mask = KEY_OTH_SETATTR; break;
        }

        key = key_ref_to_ptr(key_ref);

        /* use the second 8-bits of permissions for keys the caller owns */
        if (uid_eq(key->uid, cred->fsuid)) {
                kperm = key->perm >> 16;
                goto use_these_perms;
        }

        /* use the third 8-bits of permissions for keys the caller has a group
         * membership in common with */
        if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
                if (gid_eq(key->gid, cred->fsgid)) {
                        kperm = key->perm >> 8;
                        goto use_these_perms;
                }

                ret = groups_search(cred->group_info, key->gid);
                if (ret) {
                        kperm = key->perm >> 8;
                        goto use_these_perms;
                }
        }

        /* otherwise use the least-significant 8-bits */
        kperm = key->perm;

use_these_perms:

        /* use the top 8-bits of permissions for keys the caller possesses
         * - possessor permissions are additive with other permissions
         */
        if (is_key_possessed(key_ref))
                kperm |= key->perm >> 24;

        if ((kperm & mask) != mask)
                return -EACCES;

        /* let LSM be the final arbiter */
lsm:
        return security_key_permission(key_ref, cred, need_perm);
}
EXPORT_SYMBOL(key_task_permission);

/**
 * key_validate - Validate a key.
 * @key: The key to be validated.
 *
 * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
 * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
 * the key has been revoked or -EKEYEXPIRED if the key has expired.
 */
int key_validate(const struct key *key)
{
        unsigned long flags = READ_ONCE(key->flags);
        time64_t expiry = READ_ONCE(key->expiry);

        if (flags & (1 << KEY_FLAG_INVALIDATED))
                return -ENOKEY;

        /* check it's still accessible */
        if (flags & ((1 << KEY_FLAG_REVOKED) |
                     (1 << KEY_FLAG_DEAD)))
                return -EKEYREVOKED;

        /* check it hasn't expired */
        if (expiry) {
                if (ktime_get_real_seconds() >= expiry)
                        return -EKEYEXPIRED;
        }

        return 0;
}
EXPORT_SYMBOL(key_validate);