path: root/fs/tracefs/event_inode.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  event_inode.c - part of tracefs, a pseudo file system for activating tracing
 *
 *  Copyright (C) 2020-23 VMware Inc, author: Steven Rostedt <rostedt@goodmis.org>
 *  Copyright (C) 2020-23 VMware Inc, author: Ajay Kaher <akaher@vmware.com>
 *  Copyright (C) 2023 Google, author: Steven Rostedt <rostedt@goodmis.org>
 *
 *  eventfs is used to dynamically create inodes and dentries based on the
 *  meta data provided by the tracing system.
 *
 *  eventfs stores the meta-data of files/dirs and holds off on creating
 *  inodes/dentries of the files. When accessed, the eventfs will create the
 *  inodes/dentries in a just-in-time (JIT) manner. The eventfs will clean up
 *  and delete the inodes/dentries when they are no longer referenced.
 */
#include <linux/fsnotify.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/workqueue.h>
#include <linux/security.h>
#include <linux/tracefs.h>
#include <linux/kref.h>
#include <linux/delay.h>
#include "internal.h"

/*
 * eventfs_mutex protects the eventfs_inode (ei) dentry. Any access
 * to the ei->dentry must be done under this mutex and after checking
 * if ei->is_freed is not set. The ei->dentry is released under the
 * mutex at the same time ei->is_freed is set. If ei->is_freed is set
 * then the ei->dentry is invalid.
 */
static DEFINE_MUTEX(eventfs_mutex);

/*
 * The eventfs_inode (ei) itself is protected by SRCU. It is released from
 * its parent's list and will have is_freed set (under eventfs_mutex).
 * After the SRCU grace period is over, the ei may be freed.
 */
DEFINE_STATIC_SRCU(eventfs_srcu);

/* Mode is unsigned short, use the upper bits for flags */
enum {
	EVENTFS_SAVE_MODE	= BIT(16),
	EVENTFS_SAVE_UID	= BIT(17),
	EVENTFS_SAVE_GID	= BIT(18),
};

#define EVENTFS_MODE_MASK	(EVENTFS_SAVE_MODE - 1)

static struct dentry *eventfs_root_lookup(struct inode *dir,
					  struct dentry *dentry,
					  unsigned int flags);
static int dcache_dir_open_wrapper(struct inode *inode, struct file *file);
static int dcache_readdir_wrapper(struct file *file, struct dir_context *ctx);
static int eventfs_release(struct inode *inode, struct file *file);

static void update_attr(struct eventfs_attr *attr, struct iattr *iattr)
{
	unsigned int ia_valid = iattr->ia_valid;

	if (ia_valid & ATTR_MODE) {
		attr->mode = (attr->mode & ~EVENTFS_MODE_MASK) |
			(iattr->ia_mode & EVENTFS_MODE_MASK) |
			EVENTFS_SAVE_MODE;
	}
	if (ia_valid & ATTR_UID) {
		attr->mode |= EVENTFS_SAVE_UID;
		attr->uid = iattr->ia_uid;
	}
	if (ia_valid & ATTR_GID) {
		attr->mode |= EVENTFS_SAVE_GID;
		attr->gid = iattr->ia_gid;
	}
}

static int eventfs_set_attr(struct mnt_idmap *idmap, struct dentry *dentry,
			    struct iattr *iattr)
{
	const struct eventfs_entry *entry;
	struct eventfs_inode *ei;
	const char *name;
	int ret;

	mutex_lock(&eventfs_mutex);
	ei = dentry->d_fsdata;
	if (ei->is_freed) {
		/* Do not allow changes if the event is about to be removed. */
		mutex_unlock(&eventfs_mutex);
		return -ENODEV;
	}

	/* Preallocate the children mode array if necessary */
	if (!(dentry->d_inode->i_mode & S_IFDIR)) {
		if (!ei->entry_attrs) {
			ei->entry_attrs = kzalloc(sizeof(*ei->entry_attrs) * ei->nr_entries,
						  GFP_KERNEL);
			if (!ei->entry_attrs) {
				ret = -ENOMEM;
				goto out;
			}
		}
	}

	ret = simple_setattr(idmap, dentry, iattr);
	if (ret < 0)
		goto out;

	/*
	 * If this is a dir, then update the ei cache, only the file
	 * mode is saved in the ei->m_children, and the ownership is
	 * determined by the parent directory.
	 */
	if (dentry->d_inode->i_mode & S_IFDIR) {
		update_attr(&ei->attr, iattr);

	} else {
		name = dentry->d_name.name;

		for (int i = 0; i < ei->nr_entries; i++) {
			entry = &ei->entries[i];
			if (strcmp(name, entry->name) == 0) {
				update_attr(&ei->entry_attrs[i], iattr);
				break;
			}
		}
	}
 out:
	mutex_unlock(&eventfs_mutex);
	return ret;
}

static const struct inode_operations eventfs_root_dir_inode_operations = {
	.lookup		= eventfs_root_lookup,
	.setattr	= eventfs_set_attr,
};

static const struct inode_operations eventfs_file_inode_operations = {
	.setattr	= eventfs_set_attr,
};

static const struct file_operations eventfs_file_operations = {
	.open		= dcache_dir_open_wrapper,
	.read		= generic_read_dir,
	.iterate_shared	= dcache_readdir_wrapper,
	.llseek		= generic_file_llseek,
	.release	= eventfs_release,
};

static void update_inode_attr(struct inode *inode, struct eventfs_attr *attr, umode_t mode)
{
	if (!attr) {
		inode->i_mode = mode;
		return;
	}

	if (attr->mode & EVENTFS_SAVE_MODE)
		inode->i_mode = attr->mode & EVENTFS_MODE_MASK;
	else
		inode->i_mode = mode;

	if (attr->mode & EVENTFS_SAVE_UID)
		inode->i_uid = attr->uid;

	if (attr->