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8c0637e950
Since the meaning of combining the KEY_NEED_* constants is undefined, make
it so that you can't do that by turning them into an enum.
The enum is also given some extra values to represent special
circumstances, such as:
(1) The '0' value is reserved and causes a warning to trap the parameter
being unset.
(2) The key is to be unlinked and we require no permissions on it, only
the keyring, (this replaces the KEY_LOOKUP_FOR_UNLINK flag).
(3) An override due to CAP_SYS_ADMIN.
(4) An override due to an instantiation token being present.
(5) The permissions check is being deferred to later key_permission()
calls.
The extra values give the opportunity for LSMs to audit these situations.
[Note: This really needs overhauling so that lookup_user_key() tells
key_task_permission() and the LSM what operation is being done and leaves
it to those functions to decide how to map that onto the available
permits. However, I don't really want to make these change in the middle
of the notifications patchset.]
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
cc: Paul Moore <paul@paul-moore.com>
cc: Stephen Smalley <stephen.smalley.work@gmail.com>
cc: Casey Schaufler <casey@schaufler-ca.com>
cc: keyrings@vger.kernel.org
cc: selinux@vger.kernel.org
124 lines
3.2 KiB
C
124 lines
3.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* Key permission checking
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*
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* Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#include <linux/export.h>
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#include <linux/security.h>
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#include "internal.h"
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/**
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* key_task_permission - Check a key can be used
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* @key_ref: The key to check.
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* @cred: The credentials to use.
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* @need_perm: The permission required.
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*
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* Check to see whether permission is granted to use a key in the desired way,
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* but permit the security modules to override.
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*
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* The caller must hold either a ref on cred or must hold the RCU readlock.
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*
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* Returns 0 if successful, -EACCES if access is denied based on the
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* permissions bits or the LSM check.
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*/
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int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
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enum key_need_perm need_perm)
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{
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struct key *key;
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key_perm_t kperm, mask;
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int ret;
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switch (need_perm) {
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default:
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WARN_ON(1);
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return -EACCES;
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case KEY_NEED_UNLINK:
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case KEY_SYSADMIN_OVERRIDE:
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case KEY_AUTHTOKEN_OVERRIDE:
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case KEY_DEFER_PERM_CHECK:
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goto lsm;
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case KEY_NEED_VIEW: mask = KEY_OTH_VIEW; break;
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case KEY_NEED_READ: mask = KEY_OTH_READ; break;
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case KEY_NEED_WRITE: mask = KEY_OTH_WRITE; break;
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case KEY_NEED_SEARCH: mask = KEY_OTH_SEARCH; break;
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case KEY_NEED_LINK: mask = KEY_OTH_LINK; break;
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case KEY_NEED_SETATTR: mask = KEY_OTH_SETATTR; break;
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}
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key = key_ref_to_ptr(key_ref);
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/* use the second 8-bits of permissions for keys the caller owns */
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if (uid_eq(key->uid, cred->fsuid)) {
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kperm = key->perm >> 16;
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goto use_these_perms;
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}
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/* use the third 8-bits of permissions for keys the caller has a group
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* membership in common with */
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if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
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if (gid_eq(key->gid, cred->fsgid)) {
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kperm = key->perm >> 8;
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goto use_these_perms;
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}
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ret = groups_search(cred->group_info, key->gid);
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if (ret) {
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kperm = key->perm >> 8;
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goto use_these_perms;
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}
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}
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/* otherwise use the least-significant 8-bits */
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kperm = key->perm;
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use_these_perms:
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/* use the top 8-bits of permissions for keys the caller possesses
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* - possessor permissions are additive with other permissions
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*/
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if (is_key_possessed(key_ref))
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kperm |= key->perm >> 24;
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if ((kperm & mask) != mask)
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return -EACCES;
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/* let LSM be the final arbiter */
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lsm:
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return security_key_permission(key_ref, cred, need_perm);
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}
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EXPORT_SYMBOL(key_task_permission);
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/**
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* key_validate - Validate a key.
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* @key: The key to be validated.
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*
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* Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
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* key is invalidated, -EKEYREVOKED if the key's type has been removed or if
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* the key has been revoked or -EKEYEXPIRED if the key has expired.
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*/
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int key_validate(const struct key *key)
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{
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unsigned long flags = READ_ONCE(key->flags);
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time64_t expiry = READ_ONCE(key->expiry);
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if (flags & (1 << KEY_FLAG_INVALIDATED))
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return -ENOKEY;
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/* check it's still accessible */
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if (flags & ((1 << KEY_FLAG_REVOKED) |
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(1 << KEY_FLAG_DEAD)))
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return -EKEYREVOKED;
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/* check it hasn't expired */
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if (expiry) {
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if (ktime_get_real_seconds() >= expiry)
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return -EKEYEXPIRED;
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}
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return 0;
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}
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EXPORT_SYMBOL(key_validate);
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