fs/overlayfs/copy_up.c - kernel/windcharger - Git at Google

 /*
  *
  * Copyright (C) 2011 Novell Inc.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published by
  * the Free Software Foundation.
  */

 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/file.h>
 #include <linux/splice.h>
 #include <linux/xattr.h>
 #include <linux/security.h>
 #include <linux/uaccess.h>
 #include "overlayfs.h"

 #define OVL_COPY_UP_CHUNK_SIZE (1 << 20)

 static int ovl_copy_up_xattr(struct dentry *old, struct dentry *new)
 {
 	ssize_t list_size, size;
 	char *buf, *name, *value;
 	int error;

 	if (!old->d_inode->i_op->getxattr ||
 	    !new->d_inode->i_op->getxattr)
 		return 0;

 	list_size = vfs_listxattr(old, NULL, 0);
 	if (list_size <= 0) {
 		if (list_size == -EOPNOTSUPP)
 			return 0;
 		return list_size;
 	}

 	buf = kzalloc(list_size, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;

 	error = -ENOMEM;
 	value = kmalloc(XATTR_SIZE_MAX, GFP_KERNEL);
 	if (!value)
 		goto out;

 	list_size = vfs_listxattr(old, buf, list_size);
 	if (list_size <= 0) {
 		error = list_size;
 		goto out_free_value;
 	}

 	for (name = buf; name < (buf + list_size); name += strlen(name) + 1) {
 		size = vfs_getxattr(old, name, value, XATTR_SIZE_MAX);
 		if (size <= 0) {
 			error = size;
 			goto out_free_value;
 		}
 		error = vfs_setxattr(new, name, value, size, 0);
 		if (error)
 			goto out_free_value;
 	}

 out_free_value:
 	kfree(value);
 out:
 	kfree(buf);
 	return error;
 }

 static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
 {
 	struct file *old_file;
 	struct file *new_file;
 	int error = 0;

 	if (len == 0)
 		return 0;

 	old_file = ovl_path_open(old, O_RDONLY);
 	if (IS_ERR(old_file))
 		return PTR_ERR(old_file);

 	new_file = ovl_path_open(new, O_WRONLY);
 	if (IS_ERR(new_file)) {
 		error = PTR_ERR(new_file);
 		goto out_fput;
 	}

 	/* FIXME: copy up sparse files efficiently */
 	while (len) {
 		loff_t offset = new_file->f_pos;
 		size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
 		long bytes;

 		if (len < this_len)
 			this_len = len;

 		if (signal_pending_state(TASK_KILLABLE, current)) {
 			error = -EINTR;
 			break;
 		}

 		bytes = do_splice_direct(old_file, &offset, new_file, this_len,
 				 SPLICE_F_MOVE);
 		if (bytes <= 0) {
 			error = bytes;
 			break;
 		}

 		len -= bytes;
 	}

 	fput(new_file);
 out_fput:
 	fput(old_file);
 	return error;
 }

 static char *ovl_read_symlink(struct dentry *realdentry)
 {
 	int res;
 	char *buf;
 	struct inode *inode = realdentry->d_inode;
 	mm_segment_t old_fs;

 	res = -EINVAL;
 	if (!inode->i_op->readlink)
 		goto err;

 	res = -ENOMEM;
 	buf = (char *) __get_free_page(GFP_KERNEL);
 	if (!buf)
 		goto err;

 	old_fs = get_fs();
 	set_fs(get_ds());
 	/* The cast to a user pointer is valid due to the set_fs() */
 	res = inode->i_op->readlink(realdentry,
 				    (char __user *)buf, PAGE_SIZE - 1);
 	set_fs(old_fs);
 	if (res < 0) {
 		free_page((unsigned long) buf);
 		goto err;
 	}
 	buf[res] = '\0';

 	return buf;

 err:
 	return ERR_PTR(res);
 }

 static int ovl_set_timestamps(struct dentry *upperdentry, struct kstat *stat)
 {
 	struct iattr attr = {
 		.ia_valid =
 		     ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET,
 		.ia_atime = stat->atime,
 		.ia_mtime = stat->mtime,
 	};

 	return notify_change(upperdentry, &attr);
 }

 static int ovl_set_mode(struct dentry *upperdentry, umode_t mode)
 {
 	struct iattr attr = {
 		.ia_valid = ATTR_MODE,
 		.ia_mode = mode,
 	};

 	return notify_change(upperdentry, &attr);
 }

 static int ovl_copy_up_locked(struct dentry *upperdir, struct dentry *dentry,
 			      struct path *lowerpath, struct kstat *stat,
 			      const char *link)
 {
 	int err;
 	struct path newpath;
 	umode_t mode = stat->mode;

 	/* Can't properly set mode on creation because of the umask */
 	stat->mode &= S_IFMT;

 	ovl_path_upper(dentry, &newpath);
 	WARN_ON(newpath.dentry);
 	newpath.dentry = ovl_upper_create(upperdir, dentry, stat, link);
 	if (IS_ERR(newpath.dentry))
 		return PTR_ERR(newpath.dentry);

 	if (S_ISREG(stat->mode)) {
 		err = ovl_copy_up_data(lowerpath, &newpath, stat->size);
 		if (err)
 			goto err_remove;
 	}

 	err = ovl_copy_up_xattr(lowerpath->dentry, newpath.dentry);
 	if (err)
 		goto err_remove;

 	mutex_lock(&newpath.dentry->d_inode->i_mutex);
 	if (!S_ISLNK(stat->mode))
 		err = ovl_set_mode(newpath.dentry, mode);
 	if (!err)
 		err = ovl_set_timestamps(newpath.dentry, stat);
 	mutex_unlock(&newpath.dentry->d_inode->i_mutex);
 	if (err)
 		goto err_remove;

 	ovl_dentry_update(dentry, newpath.dentry);

 	/*
 	 * Easiest way to get rid of the lower dentry reference is to
 	 * drop this dentry.  This is neither needed nor possible for
 	 * directories.
 	 */
 	if (!S_ISDIR(stat->mode))
 		d_drop(dentry);

 	return 0;

 err_remove:
 	if (S_ISDIR(stat->mode))
 		vfs_rmdir(upperdir->d_inode, newpath.dentry);
 	else
 		vfs_unlink(upperdir->d_inode, newpath.dentry);

 	dput(newpath.dentry);

 	return err;
 }

 /*
  * Copy up a single dentry
  *
  * Directory renames only allowed on "pure upper" (already created on
  * upper filesystem, never copied up).  Directories which are on lower or
  * are merged may not be renamed.  For these -EXDEV is returned and
  * userspace has to deal with it.  This means, when copying up a
  * directory we can rely on it and ancestors being stable.
  *
  * Non-directory renames start with copy up of source if necessary.  The
  * actual rename will only proceed once the copy up was successful.  Copy
  * up uses upper parent i_mutex for exclusion.  Since rename can change
  * d_parent it is possible that the copy up will lock the old parent.  At
  * that point the file will have already been copied up anyway.
  */
 static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 			   struct path *lowerpath, struct kstat *stat)
 {
 	int err;
 	struct kstat pstat;
 	struct path parentpath;
 	struct dentry *upperdir;
 	const struct cred *old_cred;
 	struct cred *override_cred;
 	char *link = NULL;

 	ovl_path_upper(parent, &parentpath);
 	upperdir = parentpath.dentry;

 	err = vfs_getattr(parentpath.mnt, parentpath.dentry, &pstat);
 	if (err)
 		return err;

 	if (S_ISLNK(stat->mode)) {
 		link = ovl_read_symlink(lowerpath->dentry);
 		if (IS_ERR(link))
 			return PTR_ERR(link);
 	}

 	err = -ENOMEM;
 	override_cred = prepare_creds();
 	if (!override_cred)
 		goto out_free_link;

 	override_cred->fsuid = stat->uid;
 	override_cred->fsgid = stat->gid;
 	/*
 	 * CAP_SYS_ADMIN for copying up extended attributes
 	 * CAP_DAC_OVERRIDE for create
 	 * CAP_FOWNER for chmod, timestamp update
 	 * CAP_FSETID for chmod
 	 * CAP_MKNOD for mknod
 	 */
 	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
 	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
 	cap_raise(override_cred->cap_effective, CAP_FOWNER);
 	cap_raise(override_cred->cap_effective, CAP_FSETID);
 	cap_raise(override_cred->cap_effective, CAP_MKNOD);
 	old_cred = override_creds(override_cred);

 	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
 	if (ovl_path_type(dentry) != OVL_PATH_LOWER) {
 		err = 0;
 	} else {
 		err = ovl_copy_up_locked(upperdir, dentry, lowerpath,
 					 stat, link);
 		if (!err) {
 			/* Restore timestamps on parent (best effort) */
 			ovl_set_timestamps(upperdir, &pstat);
 		}
 	}

 	mutex_unlock(&upperdir->d_inode->i_mutex);

 	revert_creds(old_cred);
 	put_cred(override_cred);

 out_free_link:
 	if (link)
 		free_page((unsigned long) link);

 	return err;
 }

 int ovl_copy_up(struct dentry *dentry)
 {
 	int err;

 	err = 0;
 	while (!err) {
 		struct dentry *next;
 		struct dentry *parent;
 		struct path lowerpath;
 		struct kstat stat;
 		enum ovl_path_type type = ovl_path_type(dentry);

 		if (type != OVL_PATH_LOWER)
 			break;

 		next = dget(dentry);
 		/* find the topmost dentry not yet copied up */
 		for (;;) {
 			parent = dget_parent(next);

 			type = ovl_path_type(parent);
 			if (type != OVL_PATH_LOWER)
 				break;

 			dput(next);
 			next = parent;
 		}

 		ovl_path_lower(next, &lowerpath);
 		err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat);
 		if (!err)
 			err = ovl_copy_up_one(parent, next, &lowerpath, &stat);

 		dput(parent);
 		dput(next);
 	}

 	return err;
 }

 /* Optimize by not copying up the file first and truncating later */
 int ovl_copy_up_truncate(struct dentry *dentry, loff_t size)
 {
 	int err;
 	struct kstat stat;
 	struct path lowerpath;
 	struct dentry *parent = dget_parent(dentry);

 	err = ovl_copy_up(parent);
 	if (err)
 		goto out_dput_parent;

 	ovl_path_lower(dentry, &lowerpath);
 	err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat);
 	if (err)
 		goto out_dput_parent;

 	if (size < stat.size)
 		stat.size = size;

 	err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);

 out_dput_parent:
 	dput(parent);
 	return err;
 }
	/*
	*
	* Copyright (C) 2011 Novell Inc.
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 as published by
	* the Free Software Foundation.
	*/

	#include <linux/fs.h>
	#include <linux/slab.h>
	#include <linux/file.h>
	#include <linux/splice.h>
	#include <linux/xattr.h>
	#include <linux/security.h>
	#include <linux/uaccess.h>
	#include "overlayfs.h"

	#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)

	static int ovl_copy_up_xattr(struct dentry old, struct dentry new)
	{
	ssize_t list_size, size;
	char buf, name, *value;
	int error;

	if (!old->d_inode->i_op->getxattr \|\|
	!new->d_inode->i_op->getxattr)
	return 0;

	list_size = vfs_listxattr(old, NULL, 0);
	if (list_size <= 0) {
	if (list_size == -EOPNOTSUPP)
	return 0;
	return list_size;
	}

	buf = kzalloc(list_size, GFP_KERNEL);
	if (!buf)
	return -ENOMEM;

	error = -ENOMEM;
	value = kmalloc(XATTR_SIZE_MAX, GFP_KERNEL);
	if (!value)
	goto out;

	list_size = vfs_listxattr(old, buf, list_size);
	if (list_size <= 0) {
	error = list_size;
	goto out_free_value;
	}

	for (name = buf; name < (buf + list_size); name += strlen(name) + 1) {
	size = vfs_getxattr(old, name, value, XATTR_SIZE_MAX);
	if (size <= 0) {
	error = size;
	goto out_free_value;
	}
	error = vfs_setxattr(new, name, value, size, 0);
	if (error)
	goto out_free_value;
	}

	out_free_value:
	kfree(value);
	out:
	kfree(buf);
	return error;
	}

	static int ovl_copy_up_data(struct path old, struct path new, loff_t len)
	{
	struct file *old_file;
	struct file *new_file;
	int error = 0;

	if (len == 0)
	return 0;

	old_file = ovl_path_open(old, O_RDONLY);
	if (IS_ERR(old_file))
	return PTR_ERR(old_file);

	new_file = ovl_path_open(new, O_WRONLY);
	if (IS_ERR(new_file)) {
	error = PTR_ERR(new_file);
	goto out_fput;
	}

	/* FIXME: copy up sparse files efficiently */
	while (len) {
	loff_t offset = new_file->f_pos;
	size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
	long bytes;

	if (len < this_len)
	this_len = len;

	if (signal_pending_state(TASK_KILLABLE, current)) {
	error = -EINTR;
	break;
	}

	bytes = do_splice_direct(old_file, &offset, new_file, this_len,
	SPLICE_F_MOVE);
	if (bytes <= 0) {
	error = bytes;
	break;
	}

	len -= bytes;
	}

	fput(new_file);
	out_fput:
	fput(old_file);
	return error;
	}

	static char ovl_read_symlink(struct dentry realdentry)
	{
	int res;
	char *buf;
	struct inode *inode = realdentry->d_inode;
	mm_segment_t old_fs;

	res = -EINVAL;
	if (!inode->i_op->readlink)
	goto err;

	res = -ENOMEM;
	buf = (char *) __get_free_page(GFP_KERNEL);
	if (!buf)
	goto err;

	old_fs = get_fs();
	set_fs(get_ds());
	/* The cast to a user pointer is valid due to the set_fs() */
	res = inode->i_op->readlink(realdentry,
	(char __user *)buf, PAGE_SIZE - 1);
	set_fs(old_fs);
	if (res < 0) {
	free_page((unsigned long) buf);
	goto err;
	}
	buf[res] = '\0';

	return buf;

	err:
	return ERR_PTR(res);
	}

	static int ovl_set_timestamps(struct dentry upperdentry, struct kstat stat)
	{
	struct iattr attr = {
	.ia_valid =
	ATTR_ATIME \| ATTR_MTIME \| ATTR_ATIME_SET \| ATTR_MTIME_SET,
	.ia_atime = stat->atime,
	.ia_mtime = stat->mtime,
	};

	return notify_change(upperdentry, &attr);
	}

	static int ovl_set_mode(struct dentry *upperdentry, umode_t mode)
	{
	struct iattr attr = {
	.ia_valid = ATTR_MODE,
	.ia_mode = mode,
	};

	return notify_change(upperdentry, &attr);
	}

	static int ovl_copy_up_locked(struct dentry upperdir, struct dentry dentry,
	struct path lowerpath, struct kstat stat,
	const char *link)
	{
	int err;
	struct path newpath;
	umode_t mode = stat->mode;

	/* Can't properly set mode on creation because of the umask */
	stat->mode &= S_IFMT;

	ovl_path_upper(dentry, &newpath);
	WARN_ON(newpath.dentry);
	newpath.dentry = ovl_upper_create(upperdir, dentry, stat, link);
	if (IS_ERR(newpath.dentry))
	return PTR_ERR(newpath.dentry);

	if (S_ISREG(stat->mode)) {
	err = ovl_copy_up_data(lowerpath, &newpath, stat->size);
	if (err)
	goto err_remove;
	}

	err = ovl_copy_up_xattr(lowerpath->dentry, newpath.dentry);
	if (err)
	goto err_remove;

	mutex_lock(&newpath.dentry->d_inode->i_mutex);
	if (!S_ISLNK(stat->mode))
	err = ovl_set_mode(newpath.dentry, mode);
	if (!err)
	err = ovl_set_timestamps(newpath.dentry, stat);
	mutex_unlock(&newpath.dentry->d_inode->i_mutex);
	if (err)
	goto err_remove;

	ovl_dentry_update(dentry, newpath.dentry);

	/*
	* Easiest way to get rid of the lower dentry reference is to
	* drop this dentry. This is neither needed nor possible for
	* directories.
	*/
	if (!S_ISDIR(stat->mode))
	d_drop(dentry);

	return 0;

	err_remove:
	if (S_ISDIR(stat->mode))
	vfs_rmdir(upperdir->d_inode, newpath.dentry);
	else
	vfs_unlink(upperdir->d_inode, newpath.dentry);

	dput(newpath.dentry);

	return err;
	}

	/*
	* Copy up a single dentry
	*
	* Directory renames only allowed on "pure upper" (already created on
	* upper filesystem, never copied up). Directories which are on lower or
	* are merged may not be renamed. For these -EXDEV is returned and
	* userspace has to deal with it. This means, when copying up a
	* directory we can rely on it and ancestors being stable.
	*
	* Non-directory renames start with copy up of source if necessary. The
	* actual rename will only proceed once the copy up was successful. Copy
	* up uses upper parent i_mutex for exclusion. Since rename can change
	* d_parent it is possible that the copy up will lock the old parent. At
	* that point the file will have already been copied up anyway.
	*/
	static int ovl_copy_up_one(struct dentry parent, struct dentry dentry,
	struct path lowerpath, struct kstat stat)
	{
	int err;
	struct kstat pstat;
	struct path parentpath;
	struct dentry *upperdir;
	const struct cred *old_cred;
	struct cred *override_cred;
	char *link = NULL;

	ovl_path_upper(parent, &parentpath);
	upperdir = parentpath.dentry;

	err = vfs_getattr(parentpath.mnt, parentpath.dentry, &pstat);
	if (err)
	return err;

	if (S_ISLNK(stat->mode)) {
	link = ovl_read_symlink(lowerpath->dentry);
	if (IS_ERR(link))
	return PTR_ERR(link);
	}

	err = -ENOMEM;
	override_cred = prepare_creds();
	if (!override_cred)
	goto out_free_link;

	override_cred->fsuid = stat->uid;
	override_cred->fsgid = stat->gid;
	/*
	* CAP_SYS_ADMIN for copying up extended attributes
	* CAP_DAC_OVERRIDE for create
	* CAP_FOWNER for chmod, timestamp update
	* CAP_FSETID for chmod
	* CAP_MKNOD for mknod
	*/
	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
	cap_raise(override_cred->cap_effective, CAP_FOWNER);
	cap_raise(override_cred->cap_effective, CAP_FSETID);
	cap_raise(override_cred->cap_effective, CAP_MKNOD);
	old_cred = override_creds(override_cred);

	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
	if (ovl_path_type(dentry) != OVL_PATH_LOWER) {
	err = 0;
	} else {
	err = ovl_copy_up_locked(upperdir, dentry, lowerpath,
	stat, link);
	if (!err) {
	/* Restore timestamps on parent (best effort) */
	ovl_set_timestamps(upperdir, &pstat);
	}
	}

	mutex_unlock(&upperdir->d_inode->i_mutex);

	revert_creds(old_cred);
	put_cred(override_cred);

	out_free_link:
	if (link)
	free_page((unsigned long) link);

	return err;
	}

	int ovl_copy_up(struct dentry *dentry)
	{
	int err;

	err = 0;
	while (!err) {
	struct dentry *next;
	struct dentry *parent;
	struct path lowerpath;
	struct kstat stat;
	enum ovl_path_type type = ovl_path_type(dentry);

	if (type != OVL_PATH_LOWER)
	break;

	next = dget(dentry);
	/* find the topmost dentry not yet copied up */
	for (;;) {
	parent = dget_parent(next);

	type = ovl_path_type(parent);
	if (type != OVL_PATH_LOWER)
	break;

	dput(next);
	next = parent;
	}

	ovl_path_lower(next, &lowerpath);
	err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat);
	if (!err)
	err = ovl_copy_up_one(parent, next, &lowerpath, &stat);

	dput(parent);
	dput(next);
	}

	return err;
	}

	/* Optimize by not copying up the file first and truncating later */
	int ovl_copy_up_truncate(struct dentry *dentry, loff_t size)
	{
	int err;
	struct kstat stat;
	struct path lowerpath;
	struct dentry *parent = dget_parent(dentry);

	err = ovl_copy_up(parent);
	if (err)
	goto out_dput_parent;

	ovl_path_lower(dentry, &lowerpath);
	err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat);
	if (err)
	goto out_dput_parent;

	if (size < stat.size)
	stat.size = size;

	err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);

	out_dput_parent:
	dput(parent);
	return err;
	}