KEYS: Add garbage collection for dead, revoked and expired keys. [try #6] (5d135440) · Commits · e / devices / android_kernel_fairphone_FP5

Documentation/keys.txt

+18 −1

Original line number	Diff line number	Diff line
		@@ -26,7 +26,7 @@ This document has the following sections:
		- Notes on accessing payload contents
		- Defining a key type
		- Request-key callback service
		- Key access filesystem
		- Garbage collection


		============
		@@ -113,6 +113,9 @@ Each key has a number of attributes:

		(*) Dead. The key's type was unregistered, and so the key is now useless.

		Keys in the last three states are subject to garbage collection. See the
		section on "Garbage collection".


		====================
		KEY SERVICE OVERVIEW
		@@ -1231,3 +1234,17 @@ by executing:

		In this case, the program isn't required to actually attach the key to a ring;
		the rings are provided for reference.


		==================
		GARBAGE COLLECTION
		==================

		Dead keys (for which the type has been removed) will be automatically unlinked
		from those keyrings that point to them and deleted as soon as possible by a
		background garbage collector.

		Similarly, revoked and expired keys will be garbage collected, but only after a
		certain amount of time has passed. This time is set as a number of seconds in:

		/proc/sys/kernel/keys/gc_delay

include/linux/key.h

+4 −1

Original line number	Diff line number	Diff line
		@@ -129,7 +129,10 @@ struct key {
		struct rw_semaphore sem; /* change vs change sem */
		struct key_user user; / owner of this key */
		void security; / security data for this key */
		union {
		time_t expiry; /* time at which key expires (or 0) */
		time_t revoked_at; /* time at which key was revoked */
		};
		uid_t uid;
		gid_t gid;
		key_perm_t perm; /* access permissions */

security/keys/Makefile

+1 −0

Original line number	Diff line number	Diff line
		@@ -3,6 +3,7 @@
		#

		obj-y := \
		gc.o \
		key.o \
		keyring.o \
		keyctl.o \

security/keys/gc.c

0 → 100644

+193 −0

Original line number	Diff line number	Diff line
		/* Key garbage collector
		*
		* Copyright (C) 2009 Red Hat, Inc. All Rights Reserved.
		* Written by David Howells (dhowells@redhat.com)
		*
		* This program is free software; you can redistribute it and/or
		* modify it under the terms of the GNU General Public Licence
		* as published by the Free Software Foundation; either version
		* 2 of the Licence, or (at your option) any later version.
		*/

		#include <linux/module.h>
		#include <keys/keyring-type.h>
		#include "internal.h"

		/*
		* Delay between key revocation/expiry in seconds
		*/
		unsigned key_gc_delay = 5 * 60;

		/*
		* Reaper
		*/
		static void key_gc_timer_func(unsigned long);
		static void key_garbage_collector(struct work_struct *);
		static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
		static DECLARE_WORK(key_gc_work, key_garbage_collector);
		static key_serial_t key_gc_cursor; /* the last key the gc considered */
		static unsigned long key_gc_executing;
		static time_t key_gc_next_run = LONG_MAX;

		/*
		* Schedule a garbage collection run
		* - precision isn't particularly important
		*/
		void key_schedule_gc(time_t gc_at)
		{
		unsigned long expires;
		time_t now = current_kernel_time().tv_sec;

		kenter("%ld", gc_at - now);

		gc_at += key_gc_delay;

		if (now >= gc_at) {
		schedule_work(&key_gc_work);
		} else if (gc_at < key_gc_next_run) {
		expires = jiffies + (gc_at - now) * HZ;
		mod_timer(&key_gc_timer, expires);
		}
		}

		/*
		* The garbage collector timer kicked off
		*/
		static void key_gc_timer_func(unsigned long data)
		{
		kenter("");
		key_gc_next_run = LONG_MAX;
		schedule_work(&key_gc_work);
		}

		/*
		* Garbage collect pointers from a keyring
		* - return true if we altered the keyring
		*/
		static bool key_gc_keyring(struct key *keyring, time_t limit)
		{
		struct keyring_list *klist;
		struct key *key;
		int loop;

		kenter("%x", key_serial(keyring));

		if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
		goto dont_gc;

		/* scan the keyring looking for dead keys */
		klist = rcu_dereference(keyring->payload.subscriptions);
		if (!klist)
		goto dont_gc;

		for (loop = klist->nkeys - 1; loop >= 0; loop--) {
		key = klist->keys[loop];
		if (test_bit(KEY_FLAG_DEAD, &key->flags) \|\|
		(key->expiry > 0 && key->expiry <= limit))
		goto do_gc;
		}

		dont_gc:
		kleave(" = false");
		return false;

		do_gc:
		key_gc_cursor = keyring->serial;
		key_get(keyring);
		spin_unlock(&key_serial_lock);
		keyring_gc(keyring, limit);
		key_put(keyring);
		kleave(" = true");
		return true;
		}

		/*
		* Garbage collector for keys
		* - this involves scanning the keyrings for dead, expired and revoked keys
		* that have overstayed their welcome
		*/
		static void key_garbage_collector(struct work_struct *work)
		{
		struct rb_node *rb;
		key_serial_t cursor;
		struct key key, xkey;
		time_t new_timer = LONG_MAX, limit;

		kenter("");

		if (test_and_set_bit(0, &key_gc_executing)) {
		key_schedule_gc(current_kernel_time().tv_sec);
		return;
		}

		limit = current_kernel_time().tv_sec;
		if (limit > key_gc_delay)
		limit -= key_gc_delay;
		else
		limit = key_gc_delay;

		spin_lock(&key_serial_lock);

		if (RB_EMPTY_ROOT(&key_serial_tree))
		goto reached_the_end;

		cursor = key_gc_cursor;
		if (cursor < 0)
		cursor = 0;

		/* find the first key above the cursor */
		key = NULL;
		rb = key_serial_tree.rb_node;
		while (rb) {
		xkey = rb_entry(rb, struct key, serial_node);
		if (cursor < xkey->serial) {
		key = xkey;
		rb = rb->rb_left;
		} else if (cursor > xkey->serial) {
		rb = rb->rb_right;
		} else {
		rb = rb_next(rb);
		if (!rb)
		goto reached_the_end;
		key = rb_entry(rb, struct key, serial_node);
		break;
		}
		}

		if (!key)
		goto reached_the_end;

		/* trawl through the keys looking for keyrings */
		for (;;) {
		if (key->expiry > 0 && key->expiry < new_timer)
		new_timer = key->expiry;

		if (key->type == &key_type_keyring &&
		key_gc_keyring(key, limit)) {
		/* the gc ate our lock */
		schedule_work(&key_gc_work);
		goto no_unlock;
		}

		rb = rb_next(&key->serial_node);
		if (!rb) {
		key_gc_cursor = 0;
		break;
		}
		key = rb_entry(rb, struct key, serial_node);
		}

		out:
		spin_unlock(&key_serial_lock);
		no_unlock:
		clear_bit(0, &key_gc_executing);
		if (new_timer < LONG_MAX)
		key_schedule_gc(new_timer);

		kleave("");
		return;

		reached_the_end:
		key_gc_cursor = 0;
		goto out;
		}

security/keys/internal.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -132,6 +132,10 @@ extern key_ref_t lookup_user_key(key_serial_t id, unsigned long flags,

		extern long join_session_keyring(const char *name);

		extern unsigned key_gc_delay;
		extern void keyring_gc(struct key *keyring, time_t limit);
		extern void key_schedule_gc(time_t expiry_at);

		/*
		* check to see whether permission is granted to use a key in the desired way
		*/