auditfilter.c

Kernel code of linux kernel

/* auditfilter.c -- filtering of audit events
 *
 * Copyright 2003-2004 Red Hat, Inc.
 * Copyright 2005 Hewlett-Packard Development Company, L.P.
 * Copyright 2005 IBM Corporation
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/kernel.h>
#include <linux/audit.h>
#include <linux/kthread.h>
#include <linux/mutex.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/netlink.h>
#include <linux/sched.h>
#include <linux/inotify.h>
#include <linux/security.h>
#include "audit.h"

/*
 * Locking model:
 *
 * audit_filter_mutex:
 * 		Synchronizes writes and blocking reads of audit's filterlist
 * 		data.  Rcu is used to traverse the filterlist and access
 * 		contents of structs audit_entry, audit_watch and opaque
 * 		LSM rules during filtering.  If modified, these structures
 * 		must be copied and replace their counterparts in the filterlist.
 * 		An audit_parent struct is not accessed during filtering, so may
 * 		be written directly provided audit_filter_mutex is held.
 */

/*
 * Reference counting:
 *
 * audit_parent: lifetime is from audit_init_parent() to receipt of an IN_IGNORED
 * 	event.  Each audit_watch holds a reference to its associated parent.
 *
 * audit_watch: if added to lists, lifetime is from audit_init_watch() to
 * 	audit_remove_watch().  Additionally, an audit_watch may exist
 * 	temporarily to assist in searching existing filter data.  Each
 * 	audit_krule holds a reference to its associated watch.
 */

struct audit_parent {
	struct list_head	ilist;	/* entry in inotify registration list */
	struct list_head	watches; /* associated watches */
	struct inotify_watch	wdata;	/* inotify watch data */
	unsigned		flags;	/* status flags */
};

/*
 * audit_parent status flags:
 *
 * AUDIT_PARENT_INVALID - set anytime rules/watches are auto-removed due to
 * a filesystem event to ensure we're adding audit watches to a valid parent.
 * Technically not needed for IN_DELETE_SELF or IN_UNMOUNT events, as we cannot
 * receive them while we have nameidata, but must be used for IN_MOVE_SELF which
 * we can receive while holding nameidata.
 */
#define AUDIT_PARENT_INVALID	0x001

/* Audit filter lists, defined in <linux/audit.h> */
struct list_head audit_filter_list[AUDIT_NR_FILTERS] = {
	LIST_HEAD_INIT(audit_filter_list[0]),
	LIST_HEAD_INIT(audit_filter_list[1]),
	LIST_HEAD_INIT(audit_filter_list[2]),
	LIST_HEAD_INIT(audit_filter_list[3]),
	LIST_HEAD_INIT(audit_filter_list[4]),
	LIST_HEAD_INIT(audit_filter_list[5]),
#if AUDIT_NR_FILTERS != 6
#error Fix audit_filter_list initialiser
#endif
};

DEFINE_MUTEX(audit_filter_mutex);

/* Inotify events we care about. */
#define AUDIT_IN_WATCH IN_MOVE|IN_CREATE|IN_DELETE|IN_DELETE_SELF|IN_MOVE_SELF

void audit_free_parent(struct inotify_watch *i_watch)
{
	struct audit_parent *parent;

	parent = container_of(i_watch, struct audit_parent, wdata);
	WARN_ON(!list_empty(&parent->watches));
	kfree(parent);
}

static inline void audit_get_watch(struct audit_watch *watch)
{
	atomic_inc(&watch->count);
}

static void audit_put_watch(struct audit_watch *watch)
{
	if (atomic_dec_and_test(&watch->count)) {
		WARN_ON(watch->parent);
		WARN_ON(!list_empty(&watch->rules));
		kfree(watch->path);
		kfree(watch);
	}
}

static void audit_remove_watch(struct audit_watch *watch)
{
	list_del(&watch->wlist);
	put_inotify_watch(&watch->parent->wdata);
	watch->parent = NULL;
	audit_put_watch(watch); /* match initial get */
}

static inline void audit_free_rule(struct audit_entry *e)
{
	int i;

	/* some rules don't have associated watches */
	if (e->rule.watch)
		audit_put_watch(e->rule.watch);
	if (e->rule.fields)
		for (i = 0; i < e->rule.field_count; i++) {
			struct audit_field *f = &e->rule.fields[i];
			kfree(f->lsm_str);
			security_audit_rule_free(f->lsm_rule);
		}
	kfree(e->rule.fields);
	kfree(e->rule.filterkey);
	kfree(e);
}

void audit_free_rule_rcu(struct rcu_head *head)
{
	struct audit_entry *e = container_of(head, struct audit_entry, rcu);
	audit_free_rule(e);
}

/* Initialize a parent watch entry. */
static struct audit_parent *audit_init_parent(struct nameidata *ndp)
{
	struct audit_parent *parent;
	s32 wd;

	parent = kzalloc(sizeof(*parent), GFP_KERNEL);
	if (unlikely(!parent))
		return ERR_PTR(-ENOMEM);

	INIT_LIST_HEAD(&parent->watches);
	parent->flags = 0;

	inotify_init_watch(&parent->wdata);
	/* grab a ref so inotify watch hangs around until we take audit_filter_mutex */
	get_inotify_watch(&parent->wdata);
	wd = inotify_add_watch(audit_ih, &parent->wdata,
			       ndp->path.dentry->d_inode, AUDIT_IN_WATCH);
	if (wd < 0) {
		audit_free_parent(&parent->wdata);
		return ERR_PTR(wd);
	}

	return parent;
}

/* Initialize a watch entry. */
static struct audit_watch *audit_init_watch(char *path)
{
	struct audit_watch *watch;

	watch = kzalloc(sizeof(*watch), GFP_KERNEL);
	if (unlikely(!watch))
		return ERR_PTR(-ENOMEM);

	INIT_LIST_HEAD(&watch->rules);
	atomic_set(&watch->count, 1);
	watch->path = path;
	watch->dev = (dev_t)-1;
	watch->ino = (unsigned long)-1;

	return watch;
}

/* Initialize an audit filterlist entry. */
static inline struct audit_entry *audit_init_entry(u32 field_count)
{
	struct audit_entry *entry;
	struct audit_field *fields;

	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
	if (unlikely(!entry))
		return NULL;

	fields = kzalloc(sizeof(*fields) * field_count, GFP_KERNEL);
	if (unlikely(!fields)) {
		kfree(entry);
		return NULL;
	}
	entry->rule.fields = fields;

	return entry;
}

/* Unpack a filter field's string representation from user-space
 * buffer. */
char *audit_unpack_string(void **bufp, size_t *remain, size_t len)
{
	char *str;

	if (!*bufp || (len == 0) || (len > *remain))
		return ERR_PTR(-EINVAL);

	/* Of the currently implemented string fields, PATH_MAX
	 * defines the longest valid length.
	 */
	if (len > PATH_MAX)
		return ERR_PTR(-ENAMETOOLONG);

	str = kmalloc(len + 1, GFP_KERNEL);
	if (unlikely(!str))
		return ERR_PTR(-ENOMEM);

	memcpy(str, *bufp, len);
	str[len] = 0;
	*bufp += len;
	*remain -= len;

	return str;
}

/* Translate an inode field to kernel respresentation. */
static inline int audit_to_inode(struct audit_krule *krule,
				 struct audit_field *f)
{
	if (krule->listnr != AUDIT_FILTER_EXIT ||
	    krule->watch || krule->inode_f || krule->tree)
		return -EINVAL;

	krule->inode_f = f;
	return 0;
}

/* Translate a watch string to kernel respresentation. */
static int audit_to_watch(struct audit_krule *krule, char *path, int len,
			  u32 op)
{
	struct audit_watch *watch;

	if (!audit_ih)
		return -EOPNOTSUPP;

	if (path[0] != '/' || path[len-1] == '/' ||
	    krule->listnr != AUDIT_FILTER_EXIT ||
	    op & ~AUDIT_EQUAL ||
	    krule->inode_f || krule->watch || krule->tree)
		return -EINVAL;

	watch = audit_init_watch(path);
	if (IS_ERR(watch))
		return PTR_ERR(watch);

	audit_get_watch(watch);
	krule->watch = watch;

	return 0;
}

static __u32 *classes[AUDIT_SYSCALL_CLASSES];

int __init audit_register_class(int class, unsigned *list)
{
	__u32 *p = kzalloc(AUDIT_BITMASK_SIZE * sizeof(__u32), GFP_KERNEL);
	if (!p)
		return -ENOMEM;
	while (*list != ~0U) {
		unsigned n = *list++;
		if (n >= AUDIT_BITMASK_SIZE * 32 - AUDIT_SYSCALL_CLASSES) {
			kfree(p);
			return -EINVAL;
		}
		p[AUDIT_WORD(n)] |= AUDIT_BIT(n);
	}
	if (class >= AUDIT_SYSCALL_CLASSES || classes[class]) {
		kfree(p);
		return -EINVAL;
	}
	classes[class] = p;
	return 0;
}

int audit_match_class(int class, unsigned syscall)
{
	if (unlikely(syscall >= AUDIT_BITMASK_SIZE * 32))
		return 0;
	if (unlikely(class >= AUDIT_SYSCALL_CLASSES || !classes[class]))
		return 0;
	return classes[class][AUDIT_WORD(syscall)] & AUDIT_BIT(syscall);
}

#ifdef CONFIG_AUDITSYSCALL
static inline int audit_match_class_bits(int class, u32 *mask)
{
	int i;

	if (classes[class]) {
		for (i = 0; i < AUDIT_BITMASK_SIZE; i++)
			if (mask[i] & classes[class][i])
				return 0;
	}
	return 1;
}

static int audit_match_signal(struct audit_entry *entry)
{
	struct audit_field *arch = entry->rule.arch_f;

	if (!arch) {
		/* When arch is unspecified, we must check both masks on biarch
		 * as syscall number alone is ambiguous. */
		return (audit_match_class_bits(AUDIT_CLASS_SIGNAL,
					       entry->rule.mask) &&
			audit_match_class_bits(AUDIT_CLASS_SIGNAL_32,
					       entry->rule.mask));
	}

	switch(audit_classify_arch(arch->val)) {
	case 0: /* native */
		return (audit_match_class_bits(AUDIT_CLASS_SIGNAL,
					       entry->rule.mask));
	case 1: /* 32bit on biarch */
		return (audit_match_class_bits(AUDIT_CLASS_SIGNAL_32,
					       entry->rule.mask));
	default:
		return 1;
	}
}
#endif

/* Common user-space to kernel rule translation. */
static inline struct audit_entry *audit_to_entry_common(struct audit_rule *rule)
{
	unsigned listnr;
	struct audit_entry *entry;
	int i, err;

	err = -EINVAL;
	listnr = rule->flags & ~AUDIT_FILTER_PREPEND;
	switch(listnr) {
	default:
		goto exit_err;
	case AUDIT_FILTER_USER:
	case AUDIT_FILTER_TYPE:
#ifdef CONFIG_AUDITSYSCALL
	case AUDIT_FILTER_ENTRY:
	case AUDIT_FILTER_EXIT:
	case AUDIT_FILTER_TASK:
#endif
		;
	}
	if (unlikely(rule->action == AUDIT_POSSIBLE)) {
		printk(KERN_ERR "AUDIT_POSSIBLE is deprecated\n");
		goto exit_err;
	}
	if (rule->action != AUDIT_NEVER && rule->action != AUDIT_ALWAYS)
		goto exit_err;
	if (rule->field_count > AUDIT_MAX_FIELDS)
		goto exit_err;

	err = -ENOMEM;
	entry = audit_init_entry(rule->field_count);
	if (!entry)
		goto exit_err;

	entry->rule.flags = rule->flags & AUDIT_FILTER_PREPEND;
	entry->rule.listnr = listnr;
	entry->rule.action = rule->action;
	entry->rule.field_count = rule->field_count;

	for (i = 0; i < AUDIT_BITMASK_SIZE; i++)
		entry->rule.mask[i] = rule->mask[i];

	for (i = 0; i < AUDIT_SYSCALL_CLASSES; i++) {
		int bit = AUDIT_BITMASK_SIZE * 32 - i - 1;
		__u32 *p = &entry->rule.mask[AUDIT_WORD(bit)];
		__u32 *class;

		if (!(*p & AUDIT_BIT(bit)))
			continue;
		*p &= ~AUDIT_BIT(bit);
		class = classes[i];
		if (class) {
			int j;
			for (j = 0; j < AUDIT_BITMASK_SIZE; j++)
				entry->rule.mask[j] |= class[j];
		}
	}

	return entry;

exit_err:
	return ERR_PTR(err);
}

/* Translate struct audit_rule to kernel's rule respresentation.
 * Exists for backward compatibility with userspace. */
static struct audit_entry *audit_rule_to_entry(struct audit_rule *rule)
{
	struct audit_entry *entry;
	struct audit_field *ino_f;
	int err = 0;
	int i;

	entry = audit_to_entry_common(rule);
	if (IS_ERR(entry))
		goto exit_nofree;

	for (i = 0; i < rule->field_count; i++) {
		struct audit_field *f = &entry->rule.fields[i];

		f->op = rule->fields[i] & (AUDIT_NEGATE|AUDIT_OPERATORS);
		f->type = rule->fields[i] & ~(AUDIT_NEGATE|AUDIT_OPERATORS);
		f->val = rule->values[i];

		err = -EINVAL;
		switch(f->type) {
		default:
			goto exit_free;
		case AUDIT_PID:
		case AUDIT_UID:
		case AUDIT_EUID:
		case AUDIT_SUID:
		case AUDIT_FSUID:
		case AUDIT_GID:
		case AUDIT_EGID:
		case AUDIT_SGID:
		case AUDIT_FSGID:
		case AUDIT_LOGINUID:
		case AUDIT_PERS:
		case AUDIT_MSGTYPE:
		case AUDIT_PPID:
		case AUDIT_DEVMAJOR:
		case AUDIT_DEVMINOR:
		case AUDIT_EXIT:
		case AUDIT_SUCCESS:
			/* bit ops are only useful on syscall args */
			if (f->op == AUDIT_BIT_MASK ||
						f->op == AUDIT_BIT_TEST) {
				err = -EINVAL;
				goto exit_free;
			}
			break;
		case AUDIT_ARG0: