linux/fs/overlayfs/file.c

/*
 * Copyright (C) 2017 Red Hat, 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/cred.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/xattr.h>
#include <linux/uio.h>
#include <linux/uaccess.h>
#include "overlayfs.h"

static char ovl_whatisit(struct inode *inode, struct inode *realinode)
{
	if (realinode != ovl_inode_upper(inode))
		return 'l';
	if (ovl_has_upperdata(inode))
		return 'u';
	else
		return 'm';
}

static struct file *ovl_open_realfile(const struct file *file,
				      struct inode *realinode)
{
	struct inode *inode = file_inode(file);
	struct file *realfile;
	const struct cred *old_cred;
	int flags = file->f_flags | O_NOATIME | FMODE_NONOTIFY;

	old_cred = ovl_override_creds(inode->i_sb);
	realfile = open_with_fake_path(&file->f_path, flags, realinode,
				       current_cred());
	revert_creds(old_cred);

	pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
		 file, file, ovl_whatisit(inode, realinode), file->f_flags,
		 realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);

	return realfile;
}

#define OVL_SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT)

static int ovl_change_flags(struct file *file, unsigned int flags)
{
	struct inode *inode = file_inode(file);
	int err;

	/* No atime modificaton on underlying */
	flags |= O_NOATIME | FMODE_NONOTIFY;

	/* If some flag changed that cannot be changed then something's amiss */
	if (WARN_ON((file->f_flags ^ flags) & ~OVL_SETFL_MASK))
		return -EIO;

	flags &= OVL_SETFL_MASK;

	if (((flags ^ file->f_flags) & O_APPEND) && IS_APPEND(inode))
		return -EPERM;

	if (flags & O_DIRECT) {
		if (!file->f_mapping->a_ops ||
		    !file->f_mapping->a_ops->direct_IO)
			return -EINVAL;
	}

	if (file->f_op->check_flags) {
		err = file->f_op->check_flags(flags);
		if (err)
			return err;
	}

	spin_lock(&file->f_lock);
	file->f_flags = (file->f_flags & ~OVL_SETFL_MASK) | flags;
	spin_unlock(&file->f_lock);

	return 0;
}

static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
			       bool allow_meta)
{
	struct inode *inode = file_inode(file);
	struct inode *realinode;

	real->flags = 0;
	real->file = file->private_data;

	if (allow_meta)
		realinode = ovl_inode_real(inode);
	else
		realinode = ovl_inode_realdata(inode);

	/* Has it been copied up since we'd opened it? */
	if (unlikely(file_inode(real->file) != realinode)) {
		real->flags = FDPUT_FPUT;
		real->file = ovl_open_realfile(file, realinode);

		return PTR_ERR_OR_ZERO(real->file);
	}

	/* Did the flags change since open? */
	if (unlikely((file->f_flags ^ real->file->f_flags) & ~O_NOATIME))
		return ovl_change_flags(real->file, file->f_flags);

	return 0;
}

static int ovl_real_fdget(const struct file *file, struct fd *real)
{
	return ovl_real_fdget_meta(file, real, false);
}

static int ovl_open(struct inode *inode, struct file *file)
{
	struct file *realfile;
	int err;

	err = ovl_maybe_copy_up(file_dentry(file), file->f_flags);
	if (err)
		return err;

	/* No longer need these flags, so don't pass them on to underlying fs */
	file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

	realfile = ovl_open_realfile(file, ovl_inode_realdata(inode));
	if (IS_ERR(realfile))
		return PTR_ERR(realfile);

	file->private_data = realfile;

	return 0;
}

static int ovl_release(struct inode *inode, struct file *file)
{
	fput(file->private_data);

	return 0;
}

static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
{
	struct inode *inode = file_inode(file);
	struct fd real;
	const struct cred *old_cred;
	ssize_t ret;

	/*
	 * The two special cases below do not need to involve real fs,
	 * so we can optimizing concurrent callers.
	 */
	if (offset == 0) {
		if (whence == SEEK_CUR)
			return file->f_pos;

		if (whence == SEEK_SET)
			return vfs_setpos(file, 0, 0);
	}

	ret = ovl_real_fdget(file, &real);
	if (ret)
		return ret;

	/*
	 * Overlay file f_pos is the master copy that is preserved
	 * through copy up and modified on read/write, but only real
	 * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
	 * limitations that are more strict than ->s_maxbytes for specific
	 * files, so we use the real file to perform seeks.
	 */
	inode_lock(inode);
	real.file->f_pos = file->f_pos;

	old_cred = ovl_override_creds(inode->i_sb);
	ret = vfs_llseek(real.file, offset, whence);
	revert_creds(old_cred);

	file->f_pos = real.file->f_pos;
	inode_unlock(inode);

	fdput(real);

	return ret;
}

static void ovl_file_accessed(struct file *file)
{
	struct inode *inode, *upperinode;

	if (file->f_flags & O_NOATIME)
		return;

	inode = file_inode(file);
	upperinode = ovl_inode_upper(inode);

	if (!upperinode)
		return;

	if ((!timespec64_equal(&inode->i_mtime, &upperinode->i_mtime) ||
	     !timespec64_equal(&inode->i_ctime, &upperinode->i_ctime))) {
		inode->i_mtime = upperinode->i_mtime;
		inode->i_ctime = upperinode->i_ctime;
	}

	touch_atime(&file->f_path);
}

static rwf_t ovl_iocb_to_rwf(struct kiocb *iocb)
{
	int ifl = iocb->ki_flags;
	rwf_t flags = 0;

	if (ifl & IOCB_NOWAIT)
		flags |= RWF_NOWAIT;
	if (ifl & IOCB_HIPRI)
		flags |= RWF_HIPRI;
	if (ifl & IOCB_DSYNC)
		flags |= RWF_DSYNC;
	if (ifl & IOCB_SYNC)
		flags |= RWF_SYNC;

	return flags;
}

static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
	struct file *file = iocb->ki_filp;
	struct fd real;
	const struct cred *old_cred;
	ssize_t ret;

	if (!iov_iter_count(iter))
		return 0;

	ret = ovl_real_fdget(file, &real);
	if (ret)
		return ret;

	old_cred = ovl_override_creds(file_inode(file)->i_sb);
	ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
			    ovl_iocb_to_rwf(iocb));
	revert_creds(old_cred);

	ovl_file_accessed(file);

	fdput(real);

	return ret;
}

static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
{
	struct file *file = iocb->ki_filp;
	struct inode *inode = file_inode(file);
	struct fd real;
	const struct cred *old_cred;
	ssize_t ret;

	if (!iov_iter_count(iter))
		return 0;

	inode_lock(inode);
	/* Update mode */
	ovl_copyattr(ovl_inode_real(inode), inode);
	ret = file_remove_privs(file);
	if (ret)
		goto out_unlock;

	ret = ovl_real_fdget(file, &real);
	if (ret)
		goto out_unlock;

	old_cred = ovl_override_creds(file_inode(file)->i_sb);
	file_start_write(real.file);
	ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
			     ovl_iocb_to_rwf(iocb));
	file_end_write(real.file);
	revert_creds(old_cred);

	/* Update size */
	ovl_copyattr(ovl_inode_real(inode), inode);

	fdput(real);

out_unlock:
	inode_unlock(inode);

	return ret;
}

static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
	struct fd real;
	const struct cred *old_cred;
	int ret;

	ret = ovl_real_fdget_meta(file, &real, !datasync);
	if (ret)
		return ret;

	/* Don't sync lower file for fear of receiving EROFS error */
	if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
		old_cred = ovl_override_creds(file_inode(file)->i_sb);
		ret = vfs_fsync_range(real.file, start, end, datasync);
		revert_creds(old_cred);
	}

	fdput(real);

	return ret;
}

static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
{
	struct file *realfile = file->private_data;
	const struct cred *old_cred;
	int ret;

	if (!realfile->f_op->mmap)
		return -ENODEV;

	if (WARN_ON(file != vma->vm_file))
		return -EIO;

	vma->vm_file = get_file(realfile);

	old_cred = ovl_override_creds(file_inode(file)->i_sb);
	ret = call_mmap(vma->vm_file, vma);
	revert_creds(old_cred);

	if (ret) {
		/* Drop reference count from new vm_file value */
		fput(realfile);
	} else {
		/* Drop reference count from previous vm_file value */
		fput(file);
	}

	ovl_file_accessed(file);

	return ret;
}

static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
{
	struct inode *inode = file_inode(file);
	struct fd real;
	const struct cred *old_cred;
	int ret;

	ret = ovl_real_fdget(file, &real);
	if (ret)
		return ret;

	old_cred = ovl_override_creds(file_inode(file)->i_sb);
	ret = vfs_fallocate(real.file, mode, offset, len);
	revert_creds(old_cred);

	/* Update size */
	ovl_copyattr(ovl_inode_real(inode), inode);

	fdput(real);

	return ret;
}

static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
{
	struct fd real;
	const struct cred *old_cred;
	int ret;

	ret = ovl_real_fdget(file, &real);
	if (ret)
		return ret;

	old_cred = ovl_override_creds(file_inode(file)->i_sb);
	ret = vfs_fadvise(real.file, offset, len, advice);
	revert_creds(old_cred);

	fdput(real);

	return ret;
}

static long ovl_real_ioctl(struct file *file, unsigned int cmd,
			   unsigned long arg)
{
	struct fd real;
	const struct cred *old_cred;
	long ret;

	ret = ovl_real_fdget(file, &real);
	if (ret)
		return ret;

	old_cred = ovl_override_creds(file_inode(file)->i_sb);
	ret = vfs_ioctl(real.file, cmd, arg);
	revert_creds(old_cred);

	fdput(real);

	return ret;
}

static unsigned int ovl_get_inode_flags(struct inode *inode)
{
	unsigned int flags = READ_ONCE(inode->i_flags);
	unsigned int ovl_iflags = 0;

	if (flags & S_SYNC)
		ovl_iflags |= FS_SYNC_FL;
	if (flags & S_APPEND)
		ovl_iflags |= FS_APPEND_FL;
	if (flags & S_IMMUTABLE)
		ovl_iflags |= FS_IMMUTABLE_FL;
	if (flags & S_NOATIME)
		ovl_iflags |= FS_NOATIME_FL;

	return ovl_iflags;
}

static long ovl_ioctl_set_flags(struct file *file, unsigned long arg)
{
	long ret;
	struct inode *inode = file_inode(file);
	unsigned int flags;
	unsigned int old_flags;

	if (!inode_owner_or_capable(inode))
		return -EACCES;

	if (get_user(flags, (int __user *) arg))
		return -EFAULT;

	ret = mnt_want_write_file(file);
	if (ret)
		return ret;

	inode_lock(inode);

	/* Check the capability before cred override */
	ret = -EPERM;
	old_flags = ovl_get_inode_flags(inode);
	if (((flags ^ old_flags) & (FS_APPEND_FL | FS_IMMUTABLE_FL)) &&
	    !capable(CAP_LINUX_IMMUTABLE))
		goto unlock;

	ret = ovl_maybe_copy_up(file_dentry(file), O_WRONLY);
	if (ret)
		goto unlock;

	ret = ovl_real_ioctl(file, FS_IOC_SETFLAGS, arg);

	ovl_copyflags(ovl_inode_real(inode), inode);
unlock:
	inode_unlock(inode);

	mnt_drop_write_file(file);

	return ret;

}

static long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	long ret;

	switch (cmd) {
	case FS_IOC_GETFLAGS:
		ret = ovl_real_ioctl(file, cmd, arg);
		break;

	case FS_IOC_SETFLAGS:
		ret = ovl_ioctl_set_flags(file, arg);
		break;

	default:
		ret = -ENOTTY;
	}

	return ret;
}

static long ovl_compat_ioctl(struct file *file, unsigned int cmd,
			     unsigned long arg)
{
	switch (cmd) {
	case FS_IOC32_GETFLAGS:
		cmd = FS_IOC_GETFLAGS;
		break;

	case FS_IOC32_SETFLAGS:
		cmd = FS_IOC_SETFLAGS;
		break;

	default:
		return -ENOIOCTLCMD;
	}

	return ovl_ioctl(file, cmd, arg);
}

enum ovl_copyop {
	OVL_COPY,
	OVL_CLONE,
	OVL_DEDUPE,
};

static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
			    struct file *file_out, loff_t pos_out,
			    loff_t len, unsigned int flags, enum ovl_copyop op)
{
	struct inode *inode_out = file_inode(file_out);
	struct fd real_in, real_out;
	const struct cred *old_cred;
	loff_t ret;

	ret = ovl_real_fdget(file_out, &real_out);
	if (ret)
		return ret;

	ret = ovl_real_fdget(file_in, &real_in);
	if (ret) {
		fdput(real_out);
		return ret;
	}

	old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
	switch (op) {
	case OVL_COPY:
		ret = vfs_copy_file_range(real_in.file, pos_in,
					  real_out.file, pos_out, len, flags);
		break;

	case OVL_CLONE:
		ret = vfs_clone_file_range(real_in.file, pos_in,
					   real_out.file, pos_out, len, flags);
		break;

	case OVL_DEDUPE:
		ret = vfs_dedupe_file_range_one(real_in.file, pos_in,
						real_out.file, pos_out, len,
						flags);
		break;
	}
	revert_creds(old_cred);

	/* Update size */
	ovl_copyattr(ovl_inode_real(inode_out), inode_out);

	fdput(real_in);
	fdput(real_out);

	return ret;
}

static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
				   struct file *file_out, loff_t pos_out,
				   size_t len, unsigned int flags)
{
	return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
			    OVL_COPY);
}

static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
				   struct file *file_out, loff_t pos_out,
				   loff_t len, unsigned int remap_flags)
{
	enum ovl_copyop op;

	if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
		return -EINVAL;

	if (remap_flags & REMAP_FILE_DEDUP)
		op = OVL_DEDUPE;
	else
		op = OVL_CLONE;

	/*
	 * Don't copy up because of a dedupe request, this wouldn't make sense
	 * most of the time (data would be duplicated instead of deduplicated).
	 */
	if (op == OVL_DEDUPE &&
	    (!ovl_inode_upper(file_inode(file_in)) ||
	     !ovl_inode_upper(file_inode(file_out))))
		return -EPERM;

	return ovl_copyfile(file_in, pos_in, file_out, pos_out, len,
			    remap_flags, op);
}

const struct file_operations ovl_file_operations = {
	.open		= ovl_open,
	.release	= ovl_release,
	.llseek		= ovl_llseek,
	.read_iter	= ovl_read_iter,
	.write_iter	= ovl_write_iter,
	.fsync		= ovl_fsync,
	.mmap		= ovl_mmap,
	.fallocate	= ovl_fallocate,
	.fadvise	= ovl_fadvise,
	.unlocked_ioctl	= ovl_ioctl,
	.compat_ioctl	= ovl_compat_ioctl,

	.copy_file_range	= ovl_copy_file_range,
	.remap_file_range	= ovl_remap_file_range,
};