path: root/fs/posix_acl.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2002,2003 by Andreas Gruenbacher <a.gruenbacher@computer.org>
 *
 * Fixes from William Schumacher incorporated on 15 March 2001.
 *    (Reported by Charles Bertsch, <CBertsch@microtest.com>).
 */

/*
 *  This file contains generic functions for manipulating
 *  POSIX 1003.1e draft standard 17 ACLs.
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/atomic.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/cred.h>
#include <linux/posix_acl.h>
#include <linux/posix_acl_xattr.h>
#include <linux/xattr.h>
#include <linux/export.h>
#include <linux/user_namespace.h>
#include <linux/namei.h>

static struct posix_acl **acl_by_type(struct inode *inode, int type)
{
	switch (type) {
	case ACL_TYPE_ACCESS:
		return &inode->i_acl;
	case ACL_TYPE_DEFAULT:
		return &inode->i_default_acl;
	default:
		BUG();
	}
}

struct posix_acl *get_cached_acl(struct inode *inode, int type)
{
	struct posix_acl **p = acl_by_type(inode, type);
	struct posix_acl *acl;

	for (;;) {
		rcu_read_lock();
		acl = rcu_dereference(*p);
		if (!acl || is_uncached_acl(acl) ||
		    refcount_inc_not_zero(&acl->a_refcount))
			break;
		rcu_read_unlock();
		cpu_relax();
	}
	rcu_read_unlock();
	return acl;
}
EXPORT_SYMBOL(get_cached_acl);

struct posix_acl *get_cached_acl_rcu(struct inode *inode, int type)
{
	struct posix_acl *acl = rcu_dereference(*acl_by_type(inode, type));

	if (acl == ACL_DONT_CACHE) {
		struct posix_acl *ret;

		ret = inode->i_op->get_acl(inode, type, LOOKUP_RCU);
		if (!IS_ERR(ret))
			acl = ret;
	}

	return acl;
}
EXPORT_SYMBOL(get_cached_acl_rcu);

void set_cached_acl(struct inode *inode, int type, struct posix_acl *acl)
{
	struct posix_acl **p = acl_by_type(inode, type);
	struct posix_acl *old;

	old = xchg(p, posix_acl_dup(acl));
	if (!is_uncached_acl(old))
		posix_acl_release(old);
}
EXPORT_SYMBOL(set_cached_acl);

static void __forget_cached_acl(struct posix_acl **p)
{
	struct posix_acl *old;

	old = xchg(p, ACL_NOT_CACHED);
	if (!is_uncached_acl(old))
		posix_acl_release(old);
}

void forget_cached_acl(struct inode *inode, int type)
{
	__forget_cached_acl(acl_by_type(inode, type));
}
EXPORT_SYMBOL(forget_cached_acl);

void forget_all_cached_acls(struct inode *inode)
{
	__forget_cached_acl(&inode->i_acl);
	__forget_cached_acl(&inode->i_default_acl);
}
EXPORT_SYMBOL(forget_all_cached_acls);

struct posix_acl *get_acl(struct inode *inode, int type)
{
	void *sentinel;
	struct posix_acl **p;
	struct posix_acl *acl;

	/*
	 * The sentinel is used to detect when another operation like
	 * set_cached_acl() or forget_cached_acl() races with get_acl().
	 * It is guaranteed that is_uncached_acl(sentinel) is true.
	 */

	acl = get_cached_acl(inode, type);
	if (!is_uncached_acl(acl))
		return acl;

	if (!IS_POSIXACL(inode))
		return NULL;

	sentinel = uncached_acl_sentinel(current);
	p = acl_by_type(inode, type);

	/*
	 * If the ACL isn't being read yet, set our sentinel.  Otherwise, the
	 * current value of the ACL will not be ACL_NOT_CACHED and so our own
	 * sentinel will not be set; another task will update the cache.  We
	 * could wait for that other task to complete its job, but it's easier
	 * to just call ->get_acl to fetch the ACL ourself.  (This is going to
	 * be an unlikely race.)
	 */
	if (cmpxchg(p, ACL_NOT_CACHED, sentinel) != ACL_NOT_CACHED)
		/* fall through */ ;

	/*
	 * Normally, the ACL returned by ->get_acl will be cached.
	 * A filesystem can prevent that by calling
	 * forget_cached_acl(inode, type) in ->get_acl.
	 *
	 * If the filesystem doesn't have a get_acl() function at all, we'll
	 * just create the negative cache entry.
	 */
	if (!inode->i_op->get_acl) {
		set_cached_acl(inode, type, NULL);
		return NULL;
	}
	acl = inode->i_op->get_acl(inode, type, false);

	if (IS_ERR(acl)) {
		/*
		 * Remove our sentinel so that we don't block future attempts
		 * to cache the ACL.
		 */
		cmpxchg(p, sentinel, ACL_NOT_CACHED);
		return acl;
	}

	/*
	 * Cache the result, but only if our sentinel is still in place.
	 */
	posix_acl_dup(acl);
	if (unlikely(cmpxchg(p, sentinel, acl) != sentinel))
		posix_acl_release(acl);
	return acl;
}
EXPORT_SYMBOL(get_acl);

/*
 * Init a fresh posix_acl
 */
void
posix_acl_init(struct posix_acl *acl, int count)
{
	refcount_set(&acl->a_refcount, 1);
	acl->a_count = count;
}
EXPORT_SYMBOL(posix_acl_init);

/*
 * Allocate a new ACL with the specified number of entries.
 */
struct posix_acl *
posix_acl_alloc(int count, gfp_t flags)
{
	const size_t size = sizeof(struct posix_acl) +
	                    count * sizeof(struct posix_acl_entry);
	struct posix_acl *acl = kmalloc(size, flags);
	if (acl)
		posix_acl_init(acl, count);
	return acl;
}
EXPORT_SYMBOL(posix_acl_alloc);

/*
 * Clone an ACL.
 */
static struct posix_acl *
posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
{
	struct posix_acl *clone = NULL;

	if (acl) {
		int size = sizeof(struct posix_acl) + acl->a_count *
		           sizeof(struct posix_acl_entry);
		clone = kmemdup(acl