ovl: document permission model

[thirdparty/kernel/linux.git] / fs / overlayfs / copy_up.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *
 * Copyright (C) 2011 Novell Inc.
 */

#include <linux/module.h>
#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 <linux/sched/signal.h>
#include <linux/cred.h>
#include <linux/namei.h>
#include <linux/fdtable.h>
#include <linux/ratelimit.h>
#include <linux/exportfs.h>
#include "overlayfs.h"

#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)

static int ovl_ccup_set(const char *buf, const struct kernel_param *param)
{
	pr_warn("\"check_copy_up\" module option is obsolete\n");
	return 0;
}

static int ovl_ccup_get(char *buf, const struct kernel_param *param)
{
	return sprintf(buf, "N\n");
}

module_param_call(check_copy_up, ovl_ccup_set, ovl_ccup_get, NULL, 0644);
MODULE_PARM_DESC(check_copy_up, "Obsolete; does nothing");

int ovl_copy_xattr(struct dentry *old, struct dentry *new)
{
	ssize_t list_size, size, value_size = 0;
	char *buf, *name, *value = NULL;
	int uninitialized_var(error);
	size_t slen;

	if (!(old->d_inode->i_opflags & IOP_XATTR) ||
	    !(new->d_inode->i_opflags & IOP_XATTR))
		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;

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

	for (name = buf; list_size; name += slen) {
		slen = strnlen(name, list_size) + 1;

		/* underlying fs providing us with an broken xattr list? */
		if (WARN_ON(slen > list_size)) {
			error = -EIO;
			break;
		}
		list_size -= slen;

		if (ovl_is_private_xattr(name))
			continue;
retry:
		size = vfs_getxattr(old, name, value, value_size);
		if (size == -ERANGE)
			size = vfs_getxattr(old, name, NULL, 0);

		if (size < 0) {
			error = size;
			break;
		}

		if (size > value_size) {
			void *new;

			new = krealloc(value, size, GFP_KERNEL);
			if (!new) {
				error = -ENOMEM;
				break;
			}
			value = new;
			value_size = size;
			goto retry;
		}

		error = security_inode_copy_up_xattr(name);
		if (error < 0 && error != -EOPNOTSUPP)
			break;
		if (error == 1) {
			error = 0;
			continue; /* Discard */
		}
		error = vfs_setxattr(new, name, value, size, 0);
		if (error)
			break;
	}
	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;
	loff_t old_pos = 0;
	loff_t new_pos = 0;
	loff_t cloned;
	loff_t data_pos = -1;
	loff_t hole_len;
	bool skip_hole = false;
	int error = 0;

	if (len == 0)
		return 0;

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

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

	/* Try to use clone_file_range to clone up within the same fs */
	cloned = do_clone_file_range(old_file, 0, new_file, 0, len, 0);
	if (cloned == len)
		goto out;
	/* Couldn't clone, so now we try to copy the data */

	/* Check if lower fs supports seek operation */
	if (old_file->f_mode & FMODE_LSEEK &&
	    old_file->f_op->llseek)
		skip_hole = true;

	while (len) {
		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;
		}

		/*
		 * Fill zero for hole will cost unnecessary disk space
		 * and meanwhile slow down the copy-up speed, so we do
		 * an optimization for hole during copy-up, it relies
		 * on SEEK_DATA implementation in lower fs so if lower
		 * fs does not support it, copy-up will behave as before.
		 *
		 * Detail logic of hole detection as below:
		 * When we detect next data position is larger than current
		 * position we will skip that hole, otherwise we copy
		 * data in the size of OVL_COPY_UP_CHUNK_SIZE. Actually,
		 * it may not recognize all kind of holes and sometimes
		 * only skips partial of hole area. However, it will be
		 * enough for most of the use cases.
		 */

		if (skip_hole && data_pos < old_pos) {
			data_pos = vfs_llseek(old_file, old_pos, SEEK_DATA);
			if (data_pos > old_pos) {
				hole_len = data_pos - old_pos;
				len -= hole_len;
				old_pos = new_pos = data_pos;
				continue;
			} else if (data_pos == -ENXIO) {
				break;
			} else if (data_pos < 0) {
				skip_hole = false;
			}
		}

		bytes = do_splice_direct(old_file, &old_pos,
					 new_file, &new_pos,
					 this_len, SPLICE_F_MOVE);
		if (bytes <= 0) {
			error = bytes;
			break;
		}
		WARN_ON(old_pos != new_pos);

		len -= bytes;
	}
out:
	if (!error)
		error = vfs_fsync(new_file, 0);
	fput(new_file);
out_fput:
	fput(old_file);
	return error;
}

static int ovl_set_size(struct dentry *upperdentry, struct kstat *stat)
{
	struct iattr attr = {
		.ia_valid = ATTR_SIZE,
		.ia_size = stat->size,
	};

	return notify_change(upperdentry, &attr, NULL);
}

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, NULL);
}

int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
{
	int err = 0;

	if (!S_ISLNK(stat->mode)) {
		struct iattr attr = {
			.ia_valid = ATTR_MODE,
			.ia_mode = stat->mode,
		};
		err = notify_change(upperdentry, &attr, NULL);
	}
	if (!err) {
		struct iattr attr = {
			.ia_valid = ATTR_UID | ATTR_GID,
			.ia_uid = stat->uid,
			.ia_gid = stat->gid,
		};
		err = notify_change(upperdentry, &attr, NULL);
	}
	if (!err)
		ovl_set_timestamps(upperdentry, stat);

	return err;
}

struct ovl_fh *ovl_encode_real_fh(struct dentry *real, bool is_upper)
{
	struct ovl_fh *fh;
	int fh_type, dwords;
	int buflen = MAX_HANDLE_SZ;
	uuid_t *uuid = &real->d_sb->s_uuid;
	int err;

	/* Make sure the real fid stays 32bit aligned */
	BUILD_BUG_ON(OVL_FH_FID_OFFSET % 4);
	BUILD_BUG_ON(MAX_HANDLE_SZ + OVL_FH_FID_OFFSET > 255);

	fh = kzalloc(buflen + OVL_FH_FID_OFFSET, GFP_KERNEL);
	if (!fh)
		return ERR_PTR(-ENOMEM);

	/*
	 * We encode a non-connectable file handle for non-dir, because we
	 * only need to find the lower inode number and we don't want to pay
	 * the price or reconnecting the dentry.
	 */
	dwords = buflen >> 2;
	fh_type = exportfs_encode_fh(real, (void *)fh->fb.fid, &dwords, 0);
	buflen = (dwords << 2);

	err = -EIO;
	if (WARN_ON(fh_type < 0) ||
	    WARN_ON(buflen > MAX_HANDLE_SZ) ||
	    WARN_ON(fh_type == FILEID_INVALID))
		goto out_err;

	fh->fb.version = OVL_FH_VERSION;
	fh->fb.magic = OVL_FH_MAGIC;
	fh->fb.type = fh_type;
	fh->fb.flags = OVL_FH_FLAG_CPU_ENDIAN;
	/*
	 * When we will want to decode an overlay dentry from this handle
	 * and all layers are on the same fs, if we get a disconncted real
	 * dentry when we decode fid, the only way to tell if we should assign
	 * it to upperdentry or to lowerstack is by checking this flag.
	 */
	if (is_upper)
		fh->fb.flags |= OVL_FH_FLAG_PATH_UPPER;
	fh->fb.len = sizeof(fh->fb) + buflen;
	fh->fb.uuid = *uuid;

	return fh;

out_err:
	kfree(fh);
	return ERR_PTR(err);
}

int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
		   struct dentry *upper)
{
	const struct ovl_fh *fh = NULL;
	int err;

	/*
	 * When lower layer doesn't support export operations store a 'null' fh,
	 * so we can use the overlay.origin xattr to distignuish between a copy
	 * up and a pure upper inode.
	 */
	if (ovl_can_decode_fh(lower->d_sb)) {
		fh = ovl_encode_real_fh(lower, false);
		if (IS_ERR(fh))
			return PTR_ERR(fh);
	}

	/*
	 * Do not fail when upper doesn't support xattrs.
	 */
	err = ovl_check_setxattr(dentry, upper, OVL_XATTR_ORIGIN, fh->buf,
				 fh ? fh->fb.len : 0, 0);
	kfree(fh);

	return err;
}

/* Store file handle of @upper dir in @index dir entry */
static int ovl_set_upper_fh(struct dentry *upper, struct dentry *index)
{
	const struct ovl_fh *fh;
	int err;

	fh = ovl_encode_real_fh(upper, true);
	if (IS_ERR(fh))
		return PTR_ERR(fh);

	err = ovl_do_setxattr(index, OVL_XATTR_UPPER, fh->buf, fh->fb.len, 0);

	kfree(fh);
	return err;
}

/*
 * Create and install index entry.
 *
 * Caller must hold i_mutex on indexdir.
 */
static int ovl_create_index(struct dentry *dentry, struct dentry *origin,
			    struct dentry *upper)
{
	struct dentry *indexdir = ovl_indexdir(dentry->d_sb);
	struct inode *dir = d_inode(indexdir);
	struct dentry *index = NULL;
	struct dentry *temp = NULL;
	struct qstr name = { };
	int err;

	/*
	 * For now this is only used for creating index entry for directories,
	 * because non-dir are copied up directly to index and then hardlinked
	 * to upper dir.
	 *
	 * TODO: implement create index for non-dir, so we can call it when
	 * encoding file handle for non-dir in case index does not exist.
	 */
	if (WARN_ON(!d_is_dir(dentry)))
		return -EIO;

	/* Directory not expected to be indexed before copy up */
	if (WARN_ON(ovl_test_flag(OVL_INDEX, d_inode(dentry))))
		return -EIO;

	err = ovl_get_index_name(origin, &name);
	if (err)
		return err;

	temp = ovl_create_temp(indexdir, OVL_CATTR(S_IFDIR | 0));
	err = PTR_ERR(temp);
	if (IS_ERR(temp))
		goto free_name;

	err = ovl_set_upper_fh(upper, temp);
	if (err)
		goto out;

	index = lookup_one_len(name.name, indexdir, name.len);
	if (IS_ERR(index)) {
		err = PTR_ERR(index);
	} else {
		err = ovl_do_rename(dir, temp, dir, index, 0);
		dput(index);
	}
out:
	if (err)
		ovl_cleanup(dir, temp);
	dput(temp);
free_name:
	kfree(name.name);
	return err;
}

struct ovl_copy_up_ctx {
	struct dentry *parent;
	struct dentry *dentry;
	struct path lowerpath;
	struct kstat stat;
	struct kstat pstat;
	const char *link;
	struct dentry *destdir;
	struct qstr destname;
	struct dentry *workdir;
	bool origin;
	bool indexed;
	bool metacopy;
};

static int ovl_link_up(struct ovl_copy_up_ctx *c)
{
	int err;
	struct dentry *upper;
	struct dentry *upperdir = ovl_dentry_upper(c->parent);
	struct inode *udir = d_inode(upperdir);

	/* Mark parent "impure" because it may now contain non-pure upper */
	err = ovl_set_impure(c->parent, upperdir);
	if (err)
		return err;

	err = ovl_set_nlink_lower(c->dentry);
	if (err)
		return err;

	inode_lock_nested(udir, I_MUTEX_PARENT);
	upper = lookup_one_len(c->dentry->d_name.name, upperdir,
			       c->dentry->d_name.len);
	err = PTR_ERR(upper);
	if (!IS_ERR(upper)) {
		err = ovl_do_link(ovl_dentry_upper(c->dentry), udir, upper);
		dput(upper);

		if (!err) {
			/* Restore timestamps on parent (best effort) */
			ovl_set_timestamps(upperdir, &c->pstat);
			ovl_dentry_set_upper_alias(c->dentry);
		}
	}
	inode_unlock(udir);
	if (err)
		return err;

	err = ovl_set_nlink_upper(c->dentry);

	return err;
}

static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
{
	int err;

	/*
	 * Copy up data first and then xattrs. Writing data after
	 * xattrs will remove security.capability xattr automatically.
	 */
	if (S_ISREG(c->stat.mode) && !c->metacopy) {
		struct path upperpath, datapath;

		ovl_path_upper(c->dentry, &upperpath);
		if (WARN_ON(upperpath.dentry != NULL))
			return -EIO;
		upperpath.dentry = temp;

		ovl_path_lowerdata(c->dentry, &datapath);
		err = ovl_copy_up_data(&datapath, &upperpath, c->stat.size);
		if (err)
			return err;
	}

	err = ovl_copy_xattr(c->lowerpath.dentry, temp);
	if (err)
		return err;

	/*
	 * Store identifier of lower inode in upper inode xattr to
	 * allow lookup of the copy up origin inode.
	 *
	 * Don't set origin when we are breaking the association with a lower
	 * hard link.
	 */
	if (c->origin) {
		err = ovl_set_origin(c->dentry, c->lowerpath.dentry, temp);
		if (err)
			return err;
	}

	if (c->metacopy) {
		err = ovl_check_setxattr(c->dentry, temp, OVL_XATTR_METACOPY,
					 NULL, 0, -EOPNOTSUPP);
		if (err)
			return err;
	}

	inode_lock(temp->d_inode);
	if (S_ISREG(c->stat.mode))
		err = ovl_set_size(temp, &c->stat);
	if (!err)
		err = ovl_set_attr(temp, &c->stat);
	inode_unlock(temp->d_inode);

	return err;
}

struct ovl_cu_creds {
	const struct cred *old;
	struct cred *new;
};

static int ovl_prep_cu_creds(struct dentry *dentry, struct ovl_cu_creds *cc)
{
	int err;

	cc->old = cc->new = NULL;
	err = security_inode_copy_up(dentry, &cc->new);
	if (err < 0)
		return err;

	if (cc->new)
		cc->old = override_creds(cc->new);

	return 0;
}

static void ovl_revert_cu_creds(struct ovl_cu_creds *cc)
{
	if (cc->new) {
		revert_creds(cc->old);
		put_cred(cc->new);
	}
}

/*
 * Copyup using workdir to prepare temp file.  Used when copying up directories,
 * special files or when upper fs doesn't support O_TMPFILE.
 */
static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
{
	struct inode *inode;
	struct inode *udir = d_inode(c->destdir), *wdir = d_inode(c->workdir);
	struct dentry *temp, *upper;
	struct ovl_cu_creds cc;
	int err;
	struct ovl_cattr cattr = {
		/* Can't properly set mode on creation because of the umask */
		.mode = c->stat.mode & S_IFMT,
		.rdev = c->stat.rdev,
		.link = c->link
	};

	err = ovl_lock_rename_workdir(c->workdir, c->destdir);
	if (err)
		return err;

	err = ovl_prep_cu_creds(c->dentry, &cc);
	if (err)
		goto unlock;

	temp = ovl_create_temp(c->workdir, &cattr);
	ovl_revert_cu_creds(&cc);

	err = PTR_ERR(temp);
	if (IS_ERR(temp))
		goto unlock;

	err = ovl_copy_up_inode(c, temp);
	if (err)
		goto cleanup;

	if (S_ISDIR(c->stat.mode) && c->indexed) {
		err = ovl_create_index(c->dentry, c->lowerpath.dentry, temp);
		if (err)
			goto cleanup;
	}

	upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
	err = PTR_ERR(upper);
	if (IS_ERR(upper))
		goto cleanup;

	err = ovl_do_rename(wdir, temp, udir, upper, 0);
	dput(upper);
	if (err)
		goto cleanup;

	if (!c->metacopy)
		ovl_set_upperdata(d_inode(c->dentry));
	inode = d_inode(c->dentry);
	ovl_inode_update(inode, temp);
	if (S_ISDIR(inode->i_mode))
		ovl_set_flag(OVL_WHITEOUTS, inode);
unlock:
	unlock_rename(c->workdir, c->destdir);

	return err;

cleanup:
	ovl_cleanup(wdir, temp);
	dput(temp);
	goto unlock;
}

/* Copyup using O_TMPFILE which does not require cross dir locking */
static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
{
	struct inode *udir = d_inode(c->destdir);
	struct dentry *temp, *upper;
	struct ovl_cu_creds cc;
	int err;

	err = ovl_prep_cu_creds(c->dentry, &cc);
	if (err)
		return err;

	temp = ovl_do_tmpfile(c->workdir, c->stat.mode);
	ovl_revert_cu_creds(&cc);

	if (IS_ERR(temp))
		return PTR_ERR(temp);

	err = ovl_copy_up_inode(c, temp);
	if (err)
		goto out_dput;

	inode_lock_nested(udir, I_MUTEX_PARENT);

	upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
	err = PTR_ERR(upper);
	if (!IS_ERR(upper)) {
		err = ovl_do_link(temp, udir, upper);
		dput(upper);
	}
	inode_unlock(udir);

	if (err)
		goto out_dput;

	if (!c->metacopy)
		ovl_set_upperdata(d_inode(c->dentry));
	ovl_inode_update(d_inode(c->dentry), temp);

	return 0;

out_dput:
	dput(temp);
	return err;
}

/*
 * Copy up a single dentry
 *
 * All 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_do_copy_up(struct ovl_copy_up_ctx *c)
{
	int err;
	struct ovl_fs *ofs = c->dentry->d_sb->s_fs_info;
	bool to_index = false;

	/*
	 * Indexed non-dir is copied up directly to the index entry and then
	 * hardlinked to upper dir. Indexed dir is copied up to indexdir,
	 * then index entry is created and then copied up dir installed.
	 * Copying dir up to indexdir instead of workdir simplifies locking.
	 */
	if (ovl_need_index(c->dentry)) {
		c->indexed = true;
		if (S_ISDIR(c->stat.mode))
			c->workdir = ovl_indexdir(c->dentry->d_sb);
		else
			to_index = true;
	}

	if (S_ISDIR(c->stat.mode) || c->stat.nlink == 1 || to_index)
		c->origin = true;

	if (to_index) {
		c->destdir = ovl_indexdir(c->dentry->d_sb);
		err = ovl_get_index_name(c->lowerpath.dentry, &c->destname);
		if (err)
			return err;
	} else if (WARN_ON(!c->parent)) {
		/* Disconnected dentry must be copied up to index dir */
		return -EIO;
	} else {
		/*
		 * Mark parent "impure" because it may now contain non-pure
		 * upper
		 */
		err = ovl_set_impure(c->parent, c->destdir);
		if (err)
			return err;
	}

	/* Should we copyup with O_TMPFILE or with workdir? */
	if (S_ISREG(c->stat.mode) && ofs->tmpfile)
		err = ovl_copy_up_tmpfile(c);
	else
		err = ovl_copy_up_workdir(c);
	if (err)
		goto out;

	if (c->indexed)
		ovl_set_flag(OVL_INDEX, d_inode(c->dentry));

	if (to_index) {
		/* Initialize nlink for copy up of disconnected dentry */
		err = ovl_set_nlink_upper(c->dentry);
	} else {
		struct inode *udir = d_inode(c->destdir);

		/* Restore timestamps on parent (best effort) */
		inode_lock(udir);
		ovl_set_timestamps(c->destdir, &c->pstat);
		inode_unlock(udir);

		ovl_dentry_set_upper_alias(c->dentry);
	}

out:
	if (to_index)
		kfree(c->destname.name);
	return err;
}

static bool ovl_need_meta_copy_up(struct dentry *dentry, umode_t mode,
				  int flags)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;

	if (!ofs->config.metacopy)
		return false;

	if (!S_ISREG(mode))
		return false;

	if (flags && ((OPEN_FMODE(flags) & FMODE_WRITE) || (flags & O_TRUNC)))
		return false;

	return true;
}

/* Copy up data of an inode which was copied up metadata only in the past. */
static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
{
	struct path upperpath, datapath;
	int err;
	char *capability = NULL;
	ssize_t uninitialized_var(cap_size);

	ovl_path_upper(c->dentry, &upperpath);
	if (WARN_ON(upperpath.dentry == NULL))
		return -EIO;

	ovl_path_lowerdata(c->dentry, &datapath);
	if (WARN_ON(datapath.dentry == NULL))
		return -EIO;

	if (c->stat.size) {
		err = cap_size = ovl_getxattr(upperpath.dentry, XATTR_NAME_CAPS,
					      &capability, 0);
		if (err < 0 && err != -ENODATA)
			goto out;
	}

	err = ovl_copy_up_data(&datapath, &upperpath, c->stat.size);
	if (err)
		goto out_free;

	/*
	 * Writing to upper file will clear security.capability xattr. We
	 * don't want that to happen for normal copy-up operation.
	 */
	if (capability) {
		err = ovl_do_setxattr(upperpath.dentry, XATTR_NAME_CAPS,
				      capability, cap_size, 0);
		if (err)
			goto out_free;
	}


	err = vfs_removexattr(upperpath.dentry, OVL_XATTR_METACOPY);
	if (err)
		goto out_free;

	ovl_set_upperdata(d_inode(c->dentry));
out_free:
	kfree(capability);
out:
	return err;
}

static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
			   int flags)
{
	int err;
	DEFINE_DELAYED_CALL(done);
	struct path parentpath;
	struct ovl_copy_up_ctx ctx = {
		.parent = parent,
		.dentry = dentry,
		.workdir = ovl_workdir(dentry),
	};

	if (WARN_ON(!ctx.workdir))
		return -EROFS;

	ovl_path_lower(dentry, &ctx.lowerpath);
	err = vfs_getattr(&ctx.lowerpath, &ctx.stat,
			  STATX_BASIC_STATS, AT_STATX_SYNC_AS_STAT);
	if (err)
		return err;

	ctx.metacopy = ovl_need_meta_copy_up(dentry, ctx.stat.mode, flags);

	if (parent) {
		ovl_path_upper(parent, &parentpath);
		ctx.destdir = parentpath.dentry;
		ctx.destname = dentry->d_name;

		err = vfs_getattr(&parentpath, &ctx.pstat,
				  STATX_ATIME | STATX_MTIME,
				  AT_STATX_SYNC_AS_STAT);
		if (err)
			return err;
	}

	/* maybe truncate regular file. this has no effect on dirs */
	if (flags & O_TRUNC)
		ctx.stat.size = 0;

	if (S_ISLNK(ctx.stat.mode)) {
		ctx.link = vfs_get_link(ctx.lowerpath.dentry, &done);
		if (IS_ERR(ctx.link))
			return PTR_ERR(ctx.link);
	}

	err = ovl_copy_up_start(dentry, flags);
	/* err < 0: interrupted, err > 0: raced with another copy-up */
	if (unlikely(err)) {
		if (err > 0)
			err = 0;
	} else {
		if (!ovl_dentry_upper(dentry))
			err = ovl_do_copy_up(&ctx);
		if (!err && parent && !ovl_dentry_has_upper_alias(dentry))
			err = ovl_link_up(&ctx);
		if (!err && ovl_dentry_needs_data_copy_up_locked(dentry, flags))
			err = ovl_copy_up_meta_inode_data(&ctx);
		ovl_copy_up_end(dentry);
	}
	do_delayed_call(&done);

	return err;
}

int ovl_copy_up_flags(struct dentry *dentry, int flags)
{
	int err = 0;
	const struct cred *old_cred = ovl_override_creds(dentry->d_sb);
	bool disconnected = (dentry->d_flags & DCACHE_DISCONNECTED);

	/*
	 * With NFS export, copy up can get called for a disconnected non-dir.
	 * In this case, we will copy up lower inode to index dir without
	 * linking it to upper dir.
	 */
	if (WARN_ON(disconnected && d_is_dir(dentry)))
		return -EIO;

	while (!err) {
		struct dentry *next;
		struct dentry *parent = NULL;

		if (ovl_already_copied_up(dentry, flags))
			break;

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

			if (ovl_dentry_upper(parent))
				break;

			dput(next);
			next = parent;
		}

		err = ovl_copy_up_one(parent, next, flags);

		dput(parent);
		dput(next);
	}
	revert_creds(old_cred);

	return err;
}

static bool ovl_open_need_copy_up(struct dentry *dentry, int flags)
{
	/* Copy up of disconnected dentry does not set upper alias */
	if (ovl_already_copied_up(dentry, flags))
		return false;

	if (special_file(d_inode(dentry)->i_mode))
		return false;

	if (!ovl_open_flags_need_copy_up(flags))
		return false;

	return true;
}

int ovl_maybe_copy_up(struct dentry *dentry, int flags)
{
	int err = 0;

	if (ovl_open_need_copy_up(dentry, flags)) {
		err = ovl_want_write(dentry);
		if (!err) {
			err = ovl_copy_up_flags(dentry, flags);
			ovl_drop_write(dentry);
		}
	}

	return err;
}

int ovl_copy_up_with_data(struct dentry *dentry)
{
	return ovl_copy_up_flags(dentry, O_WRONLY);
}

int ovl_copy_up(struct dentry *dentry)
{
	return ovl_copy_up_flags(dentry, 0);
}