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watch_queue: Add a key/keyring notification facility

Browse Source 
Add a key/keyring change notification facility whereby notifications about
changes in key and keyring content and attributes can be received.

Firstly, an event queue needs to be created:

	pipe2(fds, O_NOTIFICATION_PIPE);
	ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, 256);

then a notification can be set up to report notifications via that queue:

	struct watch_notification_filter filter = {
		.nr_filters = 1,
		.filters = {
			[0] = {
				.type = WATCH_TYPE_KEY_NOTIFY,
				.subtype_filter[0] = UINT_MAX,
			},
		},
	};
	ioctl(fds[1], IOC_WATCH_QUEUE_SET_FILTER, &filter);
	keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);

After that, records will be placed into the queue when events occur in
which keys are changed in some way.  Records are of the following format:

	struct key_notification {
		struct watch_notification watch;
		__u32	key_id;
		__u32	aux;
	} *n;

Where:

	n->watch.type will be WATCH_TYPE_KEY_NOTIFY.

	n->watch.subtype will indicate the type of event, such as
	NOTIFY_KEY_REVOKED.

	n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
	record.

	n->watch.info & WATCH_INFO_ID will be the second argument to
	keyctl_watch_key(), shifted.

	n->key will be the ID of the affected key.

	n->aux will hold subtype-dependent information, such as the key
	being linked into the keyring specified by n->key in the case of
	NOTIFY_KEY_LINKED.

Note that it is permissible for event records to be of variable length -
or, at least, the length may be dependent on the subtype.  Note also that
the queue can be shared between multiple notifications of various types.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
This commit is contained in:
David Howells 2020-01-14 17:07:11 +00:00
parent 998f50407f
commit f7e47677e3
12 changed files with 269 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
Documentation/security/keys/core.rst
View File

@ -1026,6 +1026,63 @@ The keyctl syscall functions are:
written into the output buffer. Verification returns 0 on success.
* Watch a key or keyring for changes::
long keyctl(KEYCTL_WATCH_KEY, key_serial_t key, int queue_fd,
const struct watch_notification_filter *filter);
This will set or remove a watch for changes on the specified key or
keyring.
"key" is the ID of the key to be watched.
"queue_fd" is a file descriptor referring to an open "/dev/watch_queue"
which manages the buffer into which notifications will be delivered.
"filter" is either NULL to remove a watch or a filter specification to
indicate what events are required from the key.
See Documentation/watch_queue.rst for more information.
Note that only one watch may be emplaced for any particular { key,
queue_fd } combination.
Notification records look like::
struct key_notification {
struct watch_notification watch;
__u32 key_id;
__u32 aux;
};
In this, watch::type will be "WATCH_TYPE_KEY_NOTIFY" and subtype will be
one of::
NOTIFY_KEY_INSTANTIATED
NOTIFY_KEY_UPDATED
NOTIFY_KEY_LINKED
NOTIFY_KEY_UNLINKED
NOTIFY_KEY_CLEARED
NOTIFY_KEY_REVOKED
NOTIFY_KEY_INVALIDATED
NOTIFY_KEY_SETATTR
Where these indicate a key being instantiated/rejected, updated, a link
being made in a keyring, a link being removed from a keyring, a keyring
being cleared, a key being revoked, a key being invalidated or a key
having one of its attributes changed (user, group, perm, timeout,
restriction).
If a watched key is deleted, a basic watch_notification will be issued
with "type" set to WATCH_TYPE_META and "subtype" set to
watch_meta_removal_notification. The watchpoint ID will be set in the
"info" field.
This needs to be configured by enabling:
"Provide key/keyring change notifications" (KEY_NOTIFICATIONS)
Kernel Services
===============

3
include/linux/key.h
View File

@ -176,6 +176,9 @@ struct key {
struct list_head graveyard_link;
struct rb_node serial_node;
};
#ifdef CONFIG_KEY_NOTIFICATIONS
struct watch_list *watchers; /* Entities watching this key for changes */
#endif
struct rw_semaphore sem; /* change vs change sem */
struct key_user *user; /* owner of this key */
void *security; /* security data for this key */

2
include/uapi/linux/keyctl.h
View File

@ -69,6 +69,7 @@
#define KEYCTL_RESTRICT_KEYRING 29 /* Restrict keys allowed to link to a keyring */
#define KEYCTL_MOVE 30 /* Move keys between keyrings */
#define KEYCTL_CAPABILITIES 31 /* Find capabilities of keyrings subsystem */
#define KEYCTL_WATCH_KEY 32 /* Watch a key or ring of keys for changes */
/* keyctl structures */
struct keyctl_dh_params {
@ -130,5 +131,6 @@ struct keyctl_pkey_params {
#define KEYCTL_CAPS0_MOVE 0x80 /* KEYCTL_MOVE supported */
#define KEYCTL_CAPS1_NS_KEYRING_NAME 0x01 /* Keyring names are per-user_namespace */
#define KEYCTL_CAPS1_NS_KEY_TAG 0x02 /* Key indexing can include a namespace tag */
#define KEYCTL_CAPS1_NOTIFICATIONS 0x04 /* Keys generate watchable notifications */
#endif /* _LINUX_KEYCTL_H */

28
include/uapi/linux/watch_queue.h
View File

@ -13,7 +13,8 @@
enum watch_notification_type {
WATCH_TYPE_META = 0, /* Special record */
WATCH_TYPE__NR = 1
WATCH_TYPE_KEY_NOTIFY = 1, /* Key change event notification */
WATCH_TYPE__NR = 2
};
enum watch_meta_notification_subtype {
@ -75,4 +76,29 @@ struct watch_notification_removal {
__u64 id; /* Type-dependent identifier */
};
/*
* Type of key/keyring change notification.
*/
enum key_notification_subtype {
NOTIFY_KEY_INSTANTIATED = 0, /* Key was instantiated (aux is error code) */
NOTIFY_KEY_UPDATED = 1, /* Key was updated */
NOTIFY_KEY_LINKED = 2, /* Key (aux) was added to watched keyring */
NOTIFY_KEY_UNLINKED = 3, /* Key (aux) was removed from watched keyring */
NOTIFY_KEY_CLEARED = 4, /* Keyring was cleared */
NOTIFY_KEY_REVOKED = 5, /* Key was revoked */
NOTIFY_KEY_INVALIDATED = 6, /* Key was invalidated */
NOTIFY_KEY_SETATTR = 7, /* Key's attributes got changed */
};
/*
* Key/keyring notification record.
* - watch.type = WATCH_TYPE_KEY_NOTIFY
* - watch.subtype = enum key_notification_type
*/
struct key_notification {
struct watch_notification watch;
__u32 key_id; /* The key/keyring affected */
__u32 aux; /* Per-type auxiliary data */
};
#endif /* _UAPI_LINUX_WATCH_QUEUE_H */

9
security/keys/Kconfig
View File

@ -116,3 +116,12 @@ config KEY_DH_OPERATIONS
in the kernel.
If you are unsure as to whether this is required, answer N.
config KEY_NOTIFICATIONS
bool "Provide key/keyring change notifications"
depends on KEYS && WATCH_QUEUE
help
This option provides support for getting change notifications on keys
and keyrings on which the caller has View permission. This makes use
of the /dev/watch_queue misc device to handle the notification
buffer and provides KEYCTL_WATCH_KEY to enable/disable watches.

3
security/keys/compat.c
View File

@ -156,6 +156,9 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,
case KEYCTL_CAPABILITIES:
return keyctl_capabilities(compat_ptr(arg2), arg3);
case KEYCTL_WATCH_KEY:
return keyctl_watch_key(arg2, arg3, arg4);
default:
return -EOPNOTSUPP;
}

5
security/keys/gc.c
View File

@ -131,6 +131,11 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
kdebug("- %u", key->serial);
key_check(key);
#ifdef CONFIG_KEY_NOTIFICATIONS
remove_watch_list(key->watchers, key->serial);
key->watchers = NULL;
#endif
/* Throw away the key data if the key is instantiated */
if (state == KEY_IS_POSITIVE && key->type->destroy)
key->type->destroy(key);

30
security/keys/internal.h
View File

@ -15,6 +15,7 @@
#include <linux/task_work.h>
#include <linux/keyctl.h>
#include <linux/refcount.h>
#include <linux/watch_queue.h>
#include <linux/compat.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
@ -99,7 +100,8 @@ extern int __key_link_begin(struct key *keyring,
const struct keyring_index_key *index_key,
struct assoc_array_edit **_edit);
extern int __key_link_check_live_key(struct key *keyring, struct key *key);
extern void __key_link(struct key *key, struct assoc_array_edit **_edit);
extern void __key_link(struct key *keyring, struct key *key,
struct assoc_array_edit **_edit);
extern void __key_link_end(struct key *keyring,
const struct keyring_index_key *index_key,
struct assoc_array_edit *edit);
@ -183,6 +185,23 @@ extern int key_task_permission(const key_ref_t key_ref,
const struct cred *cred,
key_perm_t perm);
static inline void notify_key(struct key *key,
enum key_notification_subtype subtype, u32 aux)
{
#ifdef CONFIG_KEY_NOTIFICATIONS
struct key_notification n = {
.watch.type = WATCH_TYPE_KEY_NOTIFY,
.watch.subtype = subtype,
.watch.info = watch_sizeof(n),
.key_id = key_serial(key),
.aux = aux,
};
post_watch_notification(key->watchers, &n.watch, current_cred(),
n.key_id);
#endif
}
/*
* Check to see whether permission is granted to use a key in the desired way.
*/
@ -333,6 +352,15 @@ static inline long keyctl_pkey_e_d_s(int op,
extern long keyctl_capabilities(unsigned char __user *_buffer, size_t buflen);
#ifdef CONFIG_KEY_NOTIFICATIONS
extern long keyctl_watch_key(key_serial_t, int, int);
#else
static inline long keyctl_watch_key(key_serial_t key_id, int watch_fd, int watch_id)
{
return -EOPNOTSUPP;
}
#endif
/*
* Debugging key validation
*/

36
security/keys/key.c
View File

@ -444,6 +444,7 @@ static int __key_instantiate_and_link(struct key *key,
/* mark the key as being instantiated */
atomic_inc(&key->user->nikeys);
mark_key_instantiated(key, 0);
notify_key(key, NOTIFY_KEY_INSTANTIATED, 0);
if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
awaken = 1;
@ -453,7 +454,7 @@ static int __key_instantiate_and_link(struct key *key,
if (test_bit(KEY_FLAG_KEEP, &keyring->flags))
set_bit(KEY_FLAG_KEEP, &key->flags);
__key_link(key, _edit);
__key_link(keyring, key, _edit);
}
/* disable the authorisation key */
@ -601,6 +602,7 @@ int key_reject_and_link(struct key *key,
/* mark the key as being negatively instantiated */
atomic_inc(&key->user->nikeys);
mark_key_instantiated(key, -error);
notify_key(key, NOTIFY_KEY_INSTANTIATED, -error);
key->expiry = ktime_get_real_seconds() + timeout;
key_schedule_gc(key->expiry + key_gc_delay);
@ -611,7 +613,7 @@ int key_reject_and_link(struct key *key,
/* and link it into the destination keyring */
if (keyring && link_ret == 0)
__key_link(key, &edit);
__key_link(keyring, key, &edit);
/* disable the authorisation key */
if (authkey)
@ -764,9 +766,11 @@ static inline key_ref_t __key_update(key_ref_t key_ref,
down_write(&key->sem);
ret = key->type->update(key, prep);
if (ret == 0)
if (ret == 0) {
/* Updating a negative key positively instantiates it */
mark_key_instantiated(key, 0);
notify_key(key, NOTIFY_KEY_UPDATED, 0);
}
up_write(&key->sem);
@ -1023,9 +1027,11 @@ int key_update(key_ref_t key_ref, const void *payload, size_t plen)
down_write(&key->sem);
ret = key->type->update(key, &prep);
if (ret == 0)
if (ret == 0) {
/* Updating a negative key positively instantiates it */
mark_key_instantiated(key, 0);
notify_key(key, NOTIFY_KEY_UPDATED, 0);
}
up_write(&key->sem);
@ -1057,15 +1063,17 @@ void key_revoke(struct key *key)
* instantiated
*/
down_write_nested(&key->sem, 1);
if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags) &&
key->type->revoke)
key->type->revoke(key);
if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags)) {
notify_key(key, NOTIFY_KEY_REVOKED, 0);
if (key->type->revoke)
key->type->revoke(key);
/* set the death time to no more than the expiry time */
time = ktime_get_real_seconds();
if (key->revoked_at == 0 || key->revoked_at > time) {
key->revoked_at = time;
key_schedule_gc(key->revoked_at + key_gc_delay);
/* set the death time to no more than the expiry time */
time = ktime_get_real_seconds();
if (key->revoked_at == 0 || key->revoked_at > time) {
key->revoked_at = time;
key_schedule_gc(key->revoked_at + key_gc_delay);
}
}
up_write(&key->sem);
@ -1087,8 +1095,10 @@ void key_invalidate(struct key *key)
if (!test_bit(KEY_FLAG_INVALIDATED, &key->flags)) {
down_write_nested(&key->sem, 1);
if (!test_and_set_bit(KEY_FLAG_INVALIDATED, &key->flags))
if (!test_and_set_bit(KEY_FLAG_INVALIDATED, &key->flags)) {
notify_key(key, NOTIFY_KEY_INVALIDATED, 0);
key_schedule_gc_links();
}
up_write(&key->sem);
}
}

99
security/keys/keyctl.c
View File

@ -37,7 +37,9 @@ static const unsigned char keyrings_capabilities[2] = {
KEYCTL_CAPS0_MOVE
),
[1] = (KEYCTL_CAPS1_NS_KEYRING_NAME |
KEYCTL_CAPS1_NS_KEY_TAG),
KEYCTL_CAPS1_NS_KEY_TAG |
(IS_ENABLED(CONFIG_KEY_NOTIFICATIONS) ? KEYCTL_CAPS1_NOTIFICATIONS : 0)
),
};
static int key_get_type_from_user(char *type,
@ -1039,6 +1041,7 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
if (group != (gid_t) -1)
key->gid = gid;
notify_key(key, NOTIFY_KEY_SETATTR, 0);
ret = 0;
error_put:
@ -1089,6 +1092,7 @@ long keyctl_setperm_key(key_serial_t id, key_perm_t perm)
/* if we're not the sysadmin, we can only change a key that we own */
if (capable(CAP_SYS_ADMIN) || uid_eq(key->uid, current_fsuid())) {
key->perm = perm;
notify_key(key, NOTIFY_KEY_SETATTR, 0);
ret = 0;
}
@ -1480,10 +1484,12 @@ long keyctl_set_timeout(key_serial_t id, unsigned timeout)
okay:
key = key_ref_to_ptr(key_ref);
ret = 0;
if (test_bit(KEY_FLAG_KEEP, &key->flags))
if (test_bit(KEY_FLAG_KEEP, &key->flags)) {
ret = -EPERM;
else
} else {
key_set_timeout(key, timeout);
notify_key(key, NOTIFY_KEY_SETATTR, 0);
}
key_put(key);
error:
@ -1757,6 +1763,90 @@ long keyctl_restrict_keyring(key_serial_t id, const char __user *_type,
return ret;
}
#ifdef CONFIG_KEY_NOTIFICATIONS
/*
* Watch for changes to a key.
*
* The caller must have View permission to watch a key or keyring.
*/
long keyctl_watch_key(key_serial_t id, int watch_queue_fd, int watch_id)
{
struct watch_queue *wqueue;
struct watch_list *wlist = NULL;
struct watch *watch = NULL;
struct key *key;
key_ref_t key_ref;
long ret;
if (watch_id < -1 || watch_id > 0xff)
return -EINVAL;
key_ref = lookup_user_key(id, KEY_LOOKUP_CREATE, KEY_NEED_VIEW);
if (IS_ERR(key_ref))
return PTR_ERR(key_ref);
key = key_ref_to_ptr(key_ref);
wqueue = get_watch_queue(watch_queue_fd);
if (IS_ERR(wqueue)) {
ret = PTR_ERR(wqueue);
goto err_key;
}
if (watch_id >= 0) {
ret = -ENOMEM;
if (!key->watchers) {
wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
if (!wlist)
goto err_wqueue;
init_watch_list(wlist, NULL);
}
watch = kzalloc(sizeof(*watch), GFP_KERNEL);
if (!watch)
goto err_wlist;
init_watch(watch, wqueue);
watch->id = key->serial;
watch->info_id = (u32)watch_id << WATCH_INFO_ID__SHIFT;
ret = security_watch_key(key);
if (ret < 0)
goto err_watch;
down_write(&key->sem);
if (!key->watchers) {
key->watchers = wlist;
wlist = NULL;
}
ret = add_watch_to_object(watch, key->watchers);
up_write(&key->sem);
if (ret == 0)
watch = NULL;
} else {
ret = -EBADSLT;
if (key->watchers) {
down_write(&key->sem);
ret = remove_watch_from_object(key->watchers,
wqueue, key_serial(key),
false);
up_write(&key->sem);
}
}
err_watch:
kfree(watch);
err_wlist:
kfree(wlist);
err_wqueue:
put_watch_queue(wqueue);
err_key:
key_put(key);
return ret;
}
#endif /* CONFIG_KEY_NOTIFICATIONS */
/*
* Get keyrings subsystem capabilities.
*/
@ -1926,6 +2016,9 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
case KEYCTL_CAPABILITIES:
return keyctl_capabilities((unsigned char __user *)arg2, (size_t)arg3);
case KEYCTL_WATCH_KEY:
return keyctl_watch_key((key_serial_t)arg2, (int)arg3, (int)arg4);
default:
return -EOPNOTSUPP;
}

20
security/keys/keyring.c
View File

@ -1056,12 +1056,14 @@ int keyring_restrict(key_ref_t keyring_ref, const char *type,
down_write(&keyring->sem);
down_write(&keyring_serialise_restrict_sem);
if (keyring->restrict_link)
if (keyring->restrict_link) {
ret = -EEXIST;
else if (keyring_detect_restriction_cycle(keyring, restrict_link))
} else if (keyring_detect_restriction_cycle(keyring, restrict_link)) {
ret = -EDEADLK;
else
} else {
keyring->restrict_link = restrict_link;
notify_key(keyring, NOTIFY_KEY_SETATTR, 0);
}
up_write(&keyring_serialise_restrict_sem);
up_write(&keyring->sem);
@ -1362,12 +1364,14 @@ int __key_link_check_live_key(struct key *keyring, struct key *key)
* holds at most one link to any given key of a particular type+description
* combination.
*/
void __key_link(struct key *key, struct assoc_array_edit **_edit)
void __key_link(struct key *keyring, struct key *key,
struct assoc_array_edit **_edit)
{
__key_get(key);
assoc_array_insert_set_object(*_edit, keyring_key_to_ptr(key));
assoc_array_apply_edit(*_edit);
*_edit = NULL;
notify_key(keyring, NOTIFY_KEY_LINKED, key_serial(key));
}
/*
@ -1451,7 +1455,7 @@ int key_link(struct key *keyring, struct key *key)
if (ret == 0)
ret = __key_link_check_live_key(keyring, key);
if (ret == 0)
__key_link(key, &edit);
__key_link(keyring, key, &edit);
error_end:
__key_link_end(keyring, &key->index_key, edit);
@ -1483,7 +1487,7 @@ static int __key_unlink_begin(struct key *keyring, struct key *key,
struct assoc_array_edit *edit;
BUG_ON(*_edit != NULL);
edit = assoc_array_delete(&keyring->keys, &keyring_assoc_array_ops,
&key->index_key);
if (IS_ERR(edit))
@ -1503,6 +1507,7 @@ static void __key_unlink(struct key *keyring, struct key *key,
struct assoc_array_edit **_edit)
{
assoc_array_apply_edit(*_edit);
notify_key(keyring, NOTIFY_KEY_UNLINKED, key_serial(key));
*_edit = NULL;
key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
}
@ -1621,7 +1626,7 @@ int key_move(struct key *key,
goto error;
__key_unlink(from_keyring, key, &from_edit);
__key_link(key, &to_edit);
__key_link(to_keyring, key, &to_edit);
error:
__key_link_end(to_keyring, &key->index_key, to_edit);
__key_unlink_end(from_keyring, key, from_edit);
@ -1655,6 +1660,7 @@ int keyring_clear(struct key *keyring)
} else {
if (edit)
assoc_array_apply_edit(edit);
notify_key(keyring, NOTIFY_KEY_CLEARED, 0);
key_payload_reserve(keyring, 0);
ret = 0;
}

4
security/keys/request_key.c
View File

@ -418,7 +418,7 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
goto key_already_present;
if (dest_keyring)
__key_link(key, &edit);
__key_link(dest_keyring, key, &edit);
mutex_unlock(&key_construction_mutex);
if (dest_keyring)
@ -437,7 +437,7 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
if (dest_keyring) {
ret = __key_link_check_live_key(dest_keyring, key);
if (ret == 0)
__key_link(key, &edit);
__key_link(dest_keyring, key, &edit);
__key_link_end(dest_keyring, &ctx->index_key, edit);
if (ret < 0)
goto link_check_failed;