path: root/fs/overlayfs/namei.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2011 Novell Inc.
 * Copyright (C) 2016 Red Hat, Inc.
 */

#include <linux/fs.h>
#include <linux/cred.h>
#include <linux/ctype.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/ratelimit.h>
#include <linux/mount.h>
#include <linux/exportfs.h>
#include "overlayfs.h"

struct ovl_lookup_data {
	struct super_block *sb;
	struct vfsmount *mnt;
	struct qstr name;
	bool is_dir;
	bool opaque;
	bool stop;
	bool last;
	char *redirect;
	bool metacopy;
};

static int ovl_check_redirect(const struct path *path, struct ovl_lookup_data *d,
			      size_t prelen, const char *post)
{
	int res;
	char *buf;
	struct ovl_fs *ofs = OVL_FS(d->sb);

	buf = ovl_get_redirect_xattr(ofs, path, prelen + strlen(post));
	if (IS_ERR_OR_NULL(buf))
		return PTR_ERR(buf);

	if (buf[0] == '/') {
		/*
		 * One of the ancestor path elements in an absolute path
		 * lookup in ovl_lookup_layer() could have been opaque and
		 * that will stop further lookup in lower layers (d->stop=true)
		 * But we have found an absolute redirect in descendant path
		 * element and that should force continue lookup in lower
		 * layers (reset d->stop).
		 */
		d->stop = false;
	} else {
		res = strlen(buf) + 1;
		memmove(buf + prelen, buf, res);
		memcpy(buf, d->name.name, prelen);
	}

	strcat(buf, post);
	kfree(d->redirect);
	d->redirect = buf;
	d->name.name = d->redirect;
	d->name.len = strlen(d->redirect);

	return 0;
}

static int ovl_acceptable(void *ctx, struct dentry *dentry)
{
	/*
	 * A non-dir origin may be disconnected, which is fine, because
	 * we only need it for its unique inode number.
	 */
	if (!d_is_dir(dentry))
		return 1;

	/* Don't decode a deleted empty directory */
	if (d_unhashed(dentry))
		return 0;

	/* Check if directory belongs to the layer we are decoding from */
	return is_subdir(dentry, ((struct vfsmount *)ctx)->mnt_root);
}

/*
 * Check validity of an overlay file handle buffer.
 *
 * Return 0 for a valid file handle.
 * Return -ENODATA for "origin unknown".
 * Return <0 for an invalid file handle.
 */
int ovl_check_fb_len(struct ovl_fb *fb, int fb_len)
{
	if (fb_len < sizeof(struct ovl_fb) || fb_len < fb->len)
		return -EINVAL;

	if (fb->magic != OVL_FH_MAGIC)
		return -EINVAL;

	/* Treat larger version and unknown flags as "origin unknown" */
	if (fb->version > OVL_FH_VERSION || fb->flags & ~OVL_FH_FLAG_ALL)
		return -ENODATA;

	/* Treat endianness mismatch as "origin unknown" */
	if (!(fb->flags & OVL_FH_FLAG_ANY_ENDIAN) &&
	    (fb->flags & OVL_FH_FLAG_BIG_ENDIAN) != OVL_FH_FLAG_CPU_ENDIAN)
		return -ENODATA;

	return 0;
}

static struct ovl_fh *ovl_get_fh(struct ovl_fs *ofs, struct dentry *upperdentry,
				 enum ovl_xattr ox)
{
	int res, err;
	struct ovl_fh *fh = NULL;

	res = ovl_getxattr_upper(ofs, upperdentry, ox, NULL, 0);
	if (res < 0) {
		if (res == -ENODATA || res == -EOPNOTSUPP)
			return NULL;
		goto fail;
	}
	/* Zero size value means "copied up but origin unknown" */
	if (res == 0)
		return NULL;

	fh = kzalloc(res + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
	if (!fh)
		return ERR_PTR(-ENOMEM);

	res = ovl_getxattr_upper(ofs