security/keys/permission.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /* Key permission checking
0003  *
0004  * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
0005  * Written by David Howells (dhowells@redhat.com)
0006  */
0007
0008 #include <linux/export.h>
0009 #include <linux/security.h>
0010 #include "internal.h"
0011
0012 /**
0013  * key_task_permission - Check a key can be used
0014  * @key_ref: The key to check.
0015  * @cred: The credentials to use.
0016  * @need_perm: The permission required.
0017  *
0018  * Check to see whether permission is granted to use a key in the desired way,
0019  * but permit the security modules to override.
0020  *
0021  * The caller must hold either a ref on cred or must hold the RCU readlock.
0022  *
0023  * Returns 0 if successful, -EACCES if access is denied based on the
0024  * permissions bits or the LSM check.
0025  */
0026 int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
0027             enum key_need_perm need_perm)
0028 {
0029     struct key *key;
0030     key_perm_t kperm, mask;
0031     int ret;
0032
0033     switch (need_perm) {
0034     default:
0035         WARN_ON(1);
0036         return -EACCES;
0037     case KEY_NEED_UNLINK:
0038     case KEY_SYSADMIN_OVERRIDE:
0039     case KEY_AUTHTOKEN_OVERRIDE:
0040     case KEY_DEFER_PERM_CHECK:
0041         goto lsm;
0042
0043     case KEY_NEED_VIEW: mask = KEY_OTH_VIEW;    break;
0044     case KEY_NEED_READ: mask = KEY_OTH_READ;    break;
0045     case KEY_NEED_WRITE:    mask = KEY_OTH_WRITE;   break;
0046     case KEY_NEED_SEARCH:   mask = KEY_OTH_SEARCH;  break;
0047     case KEY_NEED_LINK: mask = KEY_OTH_LINK;    break;
0048     case KEY_NEED_SETATTR:  mask = KEY_OTH_SETATTR; break;
0049     }
0050
0051     key = key_ref_to_ptr(key_ref);
0052
0053     /* use the second 8-bits of permissions for keys the caller owns */
0054     if (uid_eq(key->uid, cred->fsuid)) {
0055         kperm = key->perm >> 16;
0056         goto use_these_perms;
0057     }
0058
0059     /* use the third 8-bits of permissions for keys the caller has a group
0060      * membership in common with */
0061     if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
0062         if (gid_eq(key->gid, cred->fsgid)) {
0063             kperm = key->perm >> 8;
0064             goto use_these_perms;
0065         }
0066
0067         ret = groups_search(cred->group_info, key->gid);
0068         if (ret) {
0069             kperm = key->perm >> 8;
0070             goto use_these_perms;
0071         }
0072     }
0073
0074     /* otherwise use the least-significant 8-bits */
0075     kperm = key->perm;
0076
0077 use_these_perms:
0078
0079     /* use the top 8-bits of permissions for keys the caller possesses
0080      * - possessor permissions are additive with other permissions
0081      */
0082     if (is_key_possessed(key_ref))
0083         kperm |= key->perm >> 24;
0084
0085     if ((kperm & mask) != mask)
0086         return -EACCES;
0087
0088     /* let LSM be the final arbiter */
0089 lsm:
0090     return security_key_permission(key_ref, cred, need_perm);
0091 }
0092 EXPORT_SYMBOL(key_task_permission);
0093
0094 /**
0095  * key_validate - Validate a key.
0096  * @key: The key to be validated.
0097  *
0098  * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
0099  * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
0100  * the key has been revoked or -EKEYEXPIRED if the key has expired.
0101  */
0102 int key_validate(const struct key *key)
0103 {
0104     unsigned long flags = READ_ONCE(key->flags);
0105     time64_t expiry = READ_ONCE(key->expiry);
0106
0107     if (flags & (1 << KEY_FLAG_INVALIDATED))
0108         return -ENOKEY;
0109
0110     /* check it's still accessible */
0111     if (flags & ((1 << KEY_FLAG_REVOKED) |
0112              (1 << KEY_FLAG_DEAD)))
0113         return -EKEYREVOKED;
0114
0115     /* check it hasn't expired */
0116     if (expiry) {
0117         if (ktime_get_real_seconds() >= expiry)
0118             return -EKEYEXPIRED;
0119     }
0120
0121     return 0;
0122 }
0123 EXPORT_SYMBOL(key_validate);