watch_queue: Add a key/keyring notification facility

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>

1 files changed, 29 insertions, 1 deletions

diff --git a/security/keys/internal.h b/security/keys/internal.h
index 6d0ca48ae9a5..28e17f4f3328 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -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
  */