namei.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* CacheFiles path walking and related routines
 *
 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/fs.h>
#include <linux/namei.h>
#include "internal.h"

/*
 * Mark the backing file as being a cache file if it's not already in use.  The
 * mark tells the culling request command that it's not allowed to cull the
 * file or directory.  The caller must hold the inode lock.
 */
static bool __cachefiles_mark_inode_in_use(struct cachefiles_object *object,
					   struct dentry *dentry)
{
	struct inode *inode = d_backing_inode(dentry);
	bool can_use = false;

	if (!(inode->i_flags & S_KERNEL_FILE)) {
		inode->i_flags |= S_KERNEL_FILE;
		trace_cachefiles_mark_active(object, inode);
		can_use = true;
	} else {
		pr_notice("cachefiles: Inode already in use: %pd\n", dentry);
	}

	return can_use;
}

/*
 * Unmark a backing inode.  The caller must hold the inode lock.
 */
static void __cachefiles_unmark_inode_in_use(struct cachefiles_object *object,
					     struct dentry *dentry)
{
	struct inode *inode = d_backing_inode(dentry);

	inode->i_flags &= ~S_KERNEL_FILE;
	trace_cachefiles_mark_inactive(object, inode);
}

/*
 * get a subdirectory
 */
struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
					struct dentry *dir,
					const char *dirname,
					bool *_is_new)
{
	struct dentry *subdir;
	struct path path;
	int ret;

	_enter(",,%s", dirname);

	/* search the current directory for the element name */
	inode_lock_nested(d_inode(dir), I_MUTEX_PARENT);

retry:
	ret = cachefiles_inject_read_error();
	if (ret == 0)
		subdir = lookup_one_len(dirname, dir, strlen(dirname));
	else
		subdir = ERR_PTR(ret);
	if (IS_ERR(subdir)) {
		trace_cachefiles_vfs_error(NULL, d_backing_inode(dir),
					   PTR_ERR(subdir),
					   cachefiles_trace_lookup_error);
		if (PTR_ERR(subdir) == -ENOMEM)
			goto nomem_d_alloc;
		goto lookup_error;
	}

	_debug("subdir -> %pd %s",
	       subdir, d_backing_inode(subdir) ? "positive" : "negative");

	/* we need to create the subdir if it doesn't exist yet */
	if (d_is_negative(subdir)) {
		ret = cachefiles_has_space(cache, 1, 0);
		if (ret < 0)
			goto mkdir_error;

		_debug("attempt mkdir");

		path.mnt = cache->mnt;
		path.dentry = dir;
		ret = security_path_mkdir(&path, subdir, 0700);
		if (ret < 0)
			goto mkdir_error;
		ret = cachefiles_inject_write_error();
		if (ret == 0)
			ret = vfs_mkdir(&init_user_ns, d_inode(dir), subdir, 0700);
		if (ret < 0) {
			trace_cachefiles_vfs_error(NULL, d_inode(dir), ret,
						   cachefiles_trace_mkdir_error);
			goto mkdir_error;
		}

		if (unlikely(d_unhashed(subdir))) {
			cachefiles_put_directory(subdir);
			goto retry;
		}
		ASSERT(d_backing_inode(subdir));

		_debug("mkdir -> %pd{ino=%lu}",
		       subdir, d_backing_inode(subdir)->i_ino);
		if (_is_new)
			*_is_new = true;
	}

	/* Tell rmdir() it's not allowed to delete the subdir */
	inode_lock(d_inode(subdir));
	inode_unlock(d_inode(dir));

	if (!__cachefiles_mark_inode_in_use(NULL, subdir))
		goto mark_error;

	inode_unlock(d_inode(subdir));

	/* we need to make sure the subdir is a directory */
	ASSERT(d_backing_inode(subdir));

	if (!d_can_lookup(subdir)) {
		pr_err("%s is not a directory\n", dirname);
		ret = -EIO;
		goto check_error;
	}

	ret = -EPERM;
	if (!(d_backing_inode(subdir)->i_opflags & IOP_XATTR) ||
	    !d_backing_inode(subdir)->i_op->lookup ||
	    !d_backing_inode(subdir)->i_op->mkdir ||
	    !d_backing_inode(subdir)->i_op->rename ||
	    !d_backing_inode(subdir)->i_op->rmdir ||
	    !d_backing_inode(subdir)->i_op->unlink)
		goto check_error;

	_leave(" = [%lu]", d_backing_inode(subdir)->i_ino);
	return subdir;

check_error:
	cachefiles_put_directory(subdir);
	_leave(" = %d [check]", ret);
	return ERR_PTR(ret);

mark_error:
	inode_unlock(d_inode(subdir));
	dput(subdir);
	return ERR_PTR(-EBUSY);

mkdir_error:
	inode_unlock(d_inode(dir));
	dput(subdir);
	pr_err("mkdir %s failed with error %d\n", dirname, ret);
	return ERR_PTR(ret);

lookup_error:
	inode_unlock(d_inode(dir));
	ret = PTR_ERR(subdir);
	pr_err("Lookup %s failed with error %d\n", dirname, ret);
	return ERR_PTR(ret);

nomem_d_alloc:
	inode_unlock(d_inode(dir));
	_leave(" = -ENOMEM");
	return ERR_PTR(-ENOMEM);
}

/*
 * Put a subdirectory.
 */
void cachefiles_put_directory(struct dentry *dir)
{
	if (dir) {
		inode_lock(dir->d_inode);
		__cachefiles_unmark_inode_in_use(NULL, dir);
		inode_unlock(dir->d_inode);
		dput(dir);
	}
}