linux/fs/overlayfs/params.c

// SPDX-License-Identifier: GPL-2.0-only

#include <linux/fs.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>
#include <linux/posix_acl_xattr.h>
#include <linux/seq_file.h>
#include <linux/xattr.h>
#include "overlayfs.h"
#include "params.h"

static bool ovl_redirect_dir_def = IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_DIR);
module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
MODULE_PARM_DESC(redirect_dir,
		 "Default to on or off for the redirect_dir feature");

static bool ovl_redirect_always_follow =
	IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW);
module_param_named(redirect_always_follow, ovl_redirect_always_follow,
		   bool, 0644);
MODULE_PARM_DESC(redirect_always_follow,
		 "Follow redirects even if redirect_dir feature is turned off");

static bool ovl_xino_auto_def = IS_ENABLED(CONFIG_OVERLAY_FS_XINO_AUTO);
module_param_named(xino_auto, ovl_xino_auto_def, bool, 0644);
MODULE_PARM_DESC(xino_auto,
		 "Auto enable xino feature");

static bool ovl_index_def = IS_ENABLED(CONFIG_OVERLAY_FS_INDEX);
module_param_named(index, ovl_index_def, bool, 0644);
MODULE_PARM_DESC(index,
		 "Default to on or off for the inodes index feature");

static bool ovl_nfs_export_def = IS_ENABLED(CONFIG_OVERLAY_FS_NFS_EXPORT);
module_param_named(nfs_export, ovl_nfs_export_def, bool, 0644);
MODULE_PARM_DESC(nfs_export,
		 "Default to on or off for the NFS export feature");

static bool ovl_metacopy_def = IS_ENABLED(CONFIG_OVERLAY_FS_METACOPY);
module_param_named(metacopy, ovl_metacopy_def, bool, 0644);
MODULE_PARM_DESC(metacopy,
		 "Default to on or off for the metadata only copy up feature");

enum {
	Opt_lowerdir,
	Opt_upperdir,
	Opt_workdir,
	Opt_default_permissions,
	Opt_redirect_dir,
	Opt_index,
	Opt_uuid,
	Opt_nfs_export,
	Opt_userxattr,
	Opt_xino,
	Opt_metacopy,
	Opt_verity,
	Opt_volatile,
};

static const struct constant_table ovl_parameter_bool[] = {
	{ "on",		true  },
	{ "off",	false },
	{}
};

static const struct constant_table ovl_parameter_uuid[] = {
	{ "off",	OVL_UUID_OFF  },
	{ "null",	OVL_UUID_NULL },
	{ "auto",	OVL_UUID_AUTO },
	{ "on",		OVL_UUID_ON   },
	{}
};

static const char *ovl_uuid_mode(struct ovl_config *config)
{
	return ovl_parameter_uuid[config->uuid].name;
}

static int ovl_uuid_def(void)
{
	return OVL_UUID_AUTO;
}

static const struct constant_table ovl_parameter_xino[] = {
	{ "off",	OVL_XINO_OFF  },
	{ "auto",	OVL_XINO_AUTO },
	{ "on",		OVL_XINO_ON   },
	{}
};

const char *ovl_xino_mode(struct ovl_config *config)
{
	return ovl_parameter_xino[config->xino].name;
}

static int ovl_xino_def(void)
{
	return ovl_xino_auto_def ? OVL_XINO_AUTO : OVL_XINO_OFF;
}

const struct constant_table ovl_parameter_redirect_dir[] = {
	{ "off",	OVL_REDIRECT_OFF      },
	{ "follow",	OVL_REDIRECT_FOLLOW   },
	{ "nofollow",	OVL_REDIRECT_NOFOLLOW },
	{ "on",		OVL_REDIRECT_ON       },
	{}
};

static const char *ovl_redirect_mode(struct ovl_config *config)
{
	return ovl_parameter_redirect_dir[config->redirect_mode].name;
}

static int ovl_redirect_mode_def(void)
{
	return ovl_redirect_dir_def	  ? OVL_REDIRECT_ON :
	       ovl_redirect_always_follow ? OVL_REDIRECT_FOLLOW :
					    OVL_REDIRECT_NOFOLLOW;
}

static const struct constant_table ovl_parameter_verity[] = {
	{ "off",	OVL_VERITY_OFF     },
	{ "on",		OVL_VERITY_ON      },
	{ "require",	OVL_VERITY_REQUIRE },
	{}
};

static const char *ovl_verity_mode(struct ovl_config *config)
{
	return ovl_parameter_verity[config->verity_mode].name;
}

static int ovl_verity_mode_def(void)
{
	return OVL_VERITY_OFF;
}

#define fsparam_string_empty(NAME, OPT) \
	__fsparam(fs_param_is_string, NAME, OPT, fs_param_can_be_empty, NULL)

const struct fs_parameter_spec ovl_parameter_spec[] = {
	fsparam_string_empty("lowerdir",    Opt_lowerdir),
	fsparam_string("upperdir",          Opt_upperdir),
	fsparam_string("workdir",           Opt_workdir),
	fsparam_flag("default_permissions", Opt_default_permissions),
	fsparam_enum("redirect_dir",        Opt_redirect_dir, ovl_parameter_redirect_dir),
	fsparam_enum("index",               Opt_index, ovl_parameter_bool),
	fsparam_enum("uuid",                Opt_uuid, ovl_parameter_uuid),
	fsparam_enum("nfs_export",          Opt_nfs_export, ovl_parameter_bool),
	fsparam_flag("userxattr",           Opt_userxattr),
	fsparam_enum("xino",                Opt_xino, ovl_parameter_xino),
	fsparam_enum("metacopy",            Opt_metacopy, ovl_parameter_bool),
	fsparam_enum("verity",              Opt_verity, ovl_parameter_verity),
	fsparam_flag("volatile",            Opt_volatile),
	{}
};

static ssize_t ovl_parse_param_split_lowerdirs(char *str)
{
	ssize_t nr_layers = 1, nr_colons = 0;
	char *s, *d;

	for (s = d = str;; s++, d++) {
		if (*s == '\\') {
			s++;
		} else if (*s == ':') {
			bool next_colon = (*(s + 1) == ':');

			nr_colons++;
			if (nr_colons == 2 && next_colon) {
				pr_err("only single ':' or double '::' sequences of unescaped colons in lowerdir mount option allowed.\n");
				return -EINVAL;
			}
			/* count layers, not colons */
			if (!next_colon)
				nr_layers++;

			*d = '\0';
			continue;
		}

		*d = *s;
		if (!*s) {
			/* trailing colons */
			if (nr_colons) {
				pr_err("unescaped trailing colons in lowerdir mount option.\n");
				return -EINVAL;
			}
			break;
		}
		nr_colons = 0;
	}

	return nr_layers;
}

static int ovl_mount_dir_noesc(const char *name, struct path *path)
{
	int err = -EINVAL;

	if (!*name) {
		pr_err("empty lowerdir\n");
		goto out;
	}
	err = kern_path(name, LOOKUP_FOLLOW, path);
	if (err) {
		pr_err("failed to resolve '%s': %i\n", name, err);
		goto out;
	}
	err = -EINVAL;
	if (ovl_dentry_weird(path->dentry)) {
		pr_err("filesystem on '%s' not supported\n", name);
		goto out_put;
	}
	if (!d_is_dir(path->dentry)) {
		pr_err("'%s' not a directory\n", name);
		goto out_put;
	}
	return 0;

out_put:
	path_put_init(path);
out:
	return err;
}

static void ovl_unescape(char *s)
{
	char *d = s;

	for (;; s++, d++) {
		if (*s == '\\')
			s++;
		*d = *s;
		if (!*s)
			break;
	}
}

static int ovl_mount_dir(const char *name, struct path *path)
{
	int err = -ENOMEM;
	char *tmp = kstrdup(name, GFP_KERNEL);

	if (tmp) {
		ovl_unescape(tmp);
		err = ovl_mount_dir_noesc(tmp, path);

		if (!err && path->dentry->d_flags & DCACHE_OP_REAL) {
			pr_err("filesystem on '%s' not supported as upperdir\n",
			       tmp);
			path_put_init(path);
			err = -EINVAL;
		}
		kfree(tmp);
	}
	return err;
}

static int ovl_parse_param_upperdir(const char *name, struct fs_context *fc,
				    bool workdir)
{
	int err;
	struct ovl_fs *ofs = fc->s_fs_info;
	struct ovl_config *config = &ofs->config;
	struct ovl_fs_context *ctx = fc->fs_private;
	struct path path;
	char *dup;

	err = ovl_mount_dir(name, &path);
	if (err)
		return err;

	/*
	 * Check whether upper path is read-only here to report failures
	 * early. Don't forget to recheck when the superblock is created
	 * as the mount attributes could change.
	 */
	if (__mnt_is_readonly(path.mnt)) {
		path_put(&path);
		return -EINVAL;
	}

	dup = kstrdup(name, GFP_KERNEL);
	if (!dup) {
		path_put(&path);
		return -ENOMEM;
	}

	if (workdir) {
		kfree(config->workdir);
		config->workdir = dup;
		path_put(&ctx->work);
		ctx->work = path;
	} else {
		kfree(config->upperdir);
		config->upperdir = dup;
		path_put(&ctx->upper);
		ctx->upper = path;
	}
	return 0;
}

static void ovl_parse_param_drop_lowerdir(struct ovl_fs_context *ctx)
{
	for (size_t nr = 0; nr < ctx->nr; nr++) {
		path_put(&ctx->lower[nr].path);
		kfree(ctx->lower[nr].name);
		ctx->lower[nr].name = NULL;
	}
	ctx->nr = 0;
	ctx->nr_data = 0;
}

/*
 * Parse lowerdir= mount option:
 *
 * (1) lowerdir=/lower1:/lower2:/lower3::/data1::/data2
 *     Set "/lower1", "/lower2", and "/lower3" as lower layers and
 *     "/data1" and "/data2" as data lower layers. Any existing lower
 *     layers are replaced.
 * (2) lowerdir=:/lower4
 *     Append "/lower4" to current stack of lower layers. This requires
 *     that there already is at least one lower layer configured.
 * (3) lowerdir=::/lower5
 *     Append data "/lower5" as data lower layer. This requires that
 *     there's at least one regular lower layer present.
 */
static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
{
	int err;
	struct ovl_fs_context *ctx = fc->fs_private;
	struct ovl_fs_context_layer *l;
	char *dup = NULL, *dup_iter;
	ssize_t nr_lower = 0, nr = 0, nr_data = 0;
	bool append = false, data_layer = false;

	/*
	 * Ensure we're backwards compatible with mount(2)
	 * by allowing relative paths.
	 */

	/* drop all existing lower layers */
	if (!*name) {
		ovl_parse_param_drop_lowerdir(ctx);
		return 0;
	}

	if (strncmp(name, "::", 2) == 0) {
		/*
		 * This is a data layer.
		 * There must be at least one regular lower layer
		 * specified.
		 */
		if (ctx->nr == 0) {
			pr_err("data lower layers without regular lower layers not allowed");
			return -EINVAL;
		}

		/* Skip the leading "::". */
		name += 2;
		data_layer = true;
		/*
		 * A data layer is automatically an append as there
		 * must've been at least one regular lower layer.
		 */
		append = true;
	} else if (*name == ':') {
		/*
		 * This is a regular lower layer.
		 * If users want to append a layer enforce that they
		 * have already specified a first layer before. It's
		 * better to be strict.
		 */
		if (ctx->nr == 0) {
			pr_err("cannot append layer if no previous layer has been specified");
			return -EINVAL;
		}

		/*
		 * Once a sequence of data layers has started regular
		 * lower layers are forbidden.
		 */
		if (ctx->nr_data > 0) {
			pr_err("regular lower layers cannot follow data lower layers");
			return -EINVAL;
		}

		/* Skip the leading ":". */
		name++;
		append = true;
	}

	dup = kstrdup(name, GFP_KERNEL);
	if (!dup)
		return -ENOMEM;

	err = -EINVAL;
	nr_lower = ovl_parse_param_split_lowerdirs(dup);
	if (nr_lower < 0)
		goto out_err;

	if ((nr_lower > OVL_MAX_STACK) ||
	    (append && (size_add(ctx->nr, nr_lower) > OVL_MAX_STACK))) {
		pr_err("too many lower directories, limit is %d\n", OVL_MAX_STACK);
		goto out_err;
	}

	if (!append)
		ovl_parse_param_drop_lowerdir(ctx);

	/*
	 * (1) append
	 *
	 * We want nr <= nr_lower <= capacity We know nr > 0 and nr <=
	 * capacity. If nr == 0 this wouldn't be append. If nr +
	 * nr_lower is <= capacity then nr <= nr_lower <= capacity
	 * already holds. If nr + nr_lower exceeds capacity, we realloc.
	 *
	 * (2) replace
	 *
	 * Ensure we're backwards compatible with mount(2) which allows
	 * "lowerdir=/a:/b:/c,lowerdir=/d:/e:/f" causing the last
	 * specified lowerdir mount option to win.
	 *
	 * We want nr <= nr_lower <= capacity We know either (i) nr == 0
	 * or (ii) nr > 0. We also know nr_lower > 0. The capacity
	 * could've been changed multiple times already so we only know
	 * nr <= capacity. If nr + nr_lower > capacity we realloc,
	 * otherwise nr <= nr_lower <= capacity holds already.
	 */
	nr_lower += ctx->nr;
	if (nr_lower > ctx->capacity) {
		err = -ENOMEM;
		l = krealloc_array(ctx->lower, nr_lower, sizeof(*ctx->lower),
				   GFP_KERNEL_ACCOUNT);
		if (!l)
			goto out_err;

		ctx->lower = l;
		ctx->capacity = nr_lower;
	}

	/*
	 *   (3) By (1) and (2) we know nr <= nr_lower <= capacity.
	 *   (4) If ctx->nr == 0 => replace
	 *       We have verified above that the lowerdir mount option
	 *       isn't an append, i.e., the lowerdir mount option
	 *       doesn't start with ":" or "::".
	 * (4.1) The lowerdir mount options only contains regular lower
	 *       layers ":".
	 *       => Nothing to verify.
	 * (4.2) The lowerdir mount options contains regular ":" and
	 *       data "::" layers.
	 *       => We need to verify that data lower layers "::" aren't
	 *          followed by regular ":" lower layers
	 *   (5) If ctx->nr > 0 => append
	 *       We know that there's at least one regular layer
	 *       otherwise we would've failed when parsing the previous
	 *       lowerdir mount option.
	 * (5.1) The lowerdir mount option is a regular layer ":" append
	 *       => We need to verify that no data layers have been
	 *          specified before.
	 * (5.2) The lowerdir mount option is a data layer "::" append
	 *       We know that there's at least one regular layer or
	 *       other data layers. => There's nothing to verify.
	 */
	dup_iter = dup;
	for (nr = ctx->nr; nr < nr_lower; nr++) {
		l = &ctx->lower[nr];
		memset(l, 0, sizeof(*l));

		err = ovl_mount_dir_noesc(dup_iter, &l->path);
		if (err)
			goto out_put;

		err = -ENOMEM;
		l->name = kstrdup(dup_iter, GFP_KERNEL_ACCOUNT);
		if (!l->name)
			goto out_put;

		if (data_layer)
			nr_data++;

		/* Calling strchr() again would overrun. */
		if ((nr + 1) == nr_lower)
			break;

		err = -EINVAL;
		dup_iter = strchr(dup_iter, '\0') + 1;
		if (*dup_iter) {
			/*
			 * This is a regular layer so we require that
			 * there are no data layers.
			 */
			if ((ctx->nr_data + nr_data) > 0) {
				pr_err("regular lower layers cannot follow data lower layers");
				goto out_put;
			}

			data_layer = false;
			continue;
		}

		/* This is a data lower layer. */
		data_layer = true;
		dup_iter++;
	}
	ctx->nr = nr_lower;
	ctx->nr_data += nr_data;
	kfree(dup);
	return 0;

out_put:
	/*
	 * We know nr >= ctx->nr < nr_lower. If we failed somewhere
	 * we want to undo until nr == ctx->nr. This is correct for
	 * both ctx->nr == 0 and ctx->nr > 0.
	 */
	for (; nr >= ctx->nr; nr--) {
		l = &ctx->lower[nr];
		kfree(l->name);
		l->name = NULL;
		path_put(&l->path);

		/* don't overflow */
		if (nr == 0)
			break;
	}

out_err:
	kfree(dup);

	/* Intentionally don't realloc to a smaller size. */
	return err;
}

static int ovl_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
	int err = 0;
	struct fs_parse_result result;
	struct ovl_fs *ofs = fc->s_fs_info;
	struct ovl_config *config = &ofs->config;
	struct ovl_fs_context *ctx = fc->fs_private;
	int opt;

	if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE) {
		/*
		 * On remount overlayfs has always ignored all mount
		 * options no matter if malformed or not so for
		 * backwards compatibility we do the same here.
		 */
		if (fc->oldapi)
			return 0;

		/*
		 * Give us the freedom to allow changing mount options
		 * with the new mount api in the future. So instead of
		 * silently ignoring everything we report a proper
		 * error. This is only visible for users of the new
		 * mount api.
		 */
		return invalfc(fc, "No changes allowed in reconfigure");
	}

	opt = fs_parse(fc, ovl_parameter_spec, param, &result);
	if (opt < 0)
		return opt;

	switch (opt) {
	case Opt_lowerdir:
		err = ovl_parse_param_lowerdir(param->string, fc);
		break;
	case Opt_upperdir:
		fallthrough;
	case Opt_workdir:
		err = ovl_parse_param_upperdir(param->string, fc,
					       (Opt_workdir == opt));
		break;
	case Opt_default_permissions:
		config->default_permissions = true;
		break;
	case Opt_redirect_dir:
		config->redirect_mode = result.uint_32;
		if (config->redirect_mode == OVL_REDIRECT_OFF) {
			config->redirect_mode = ovl_redirect_always_follow ?
						OVL_REDIRECT_FOLLOW :
						OVL_REDIRECT_NOFOLLOW;
		}
		ctx->set.redirect = true;
		break;
	case Opt_index:
		config->index = result.uint_32;
		ctx->set.index = true;
		break;
	case Opt_uuid:
		config->uuid = result.uint_32;
		break;
	case Opt_nfs_export:
		config->nfs_export = result.uint_32;
		ctx->set.nfs_export = true;
		break;
	case Opt_xino:
		config->xino = result.uint_32;
		break;
	case Opt_metacopy:
		config->metacopy = result.uint_32;
		ctx->set.metacopy = true;
		break;
	case Opt_verity:
		config->verity_mode = result.uint_32;
		break;
	case Opt_volatile:
		config->ovl_volatile = true;
		break;
	case Opt_userxattr:
		config->userxattr = true;
		break;
	default:
		pr_err("unrecognized mount option \"%s\" or missing value\n",
		       param->key);
		return -EINVAL;
	}

	return err;
}

static int ovl_get_tree(struct fs_context *fc)
{
	return get_tree_nodev(fc, ovl_fill_super);
}

static inline void ovl_fs_context_free(struct ovl_fs_context *ctx)
{
	ovl_parse_param_drop_lowerdir(ctx);
	path_put(&ctx->upper);
	path_put(&ctx->work);
	kfree(ctx->lower);
	kfree(ctx);
}

static void ovl_free(struct fs_context *fc)
{
	struct ovl_fs *ofs = fc->s_fs_info;
	struct ovl_fs_context *ctx = fc->fs_private;

	/*
	 * ofs is stored in the fs_context when it is initialized.
	 * ofs is transferred to the superblock on a successful mount,
	 * but if an error occurs before the transfer we have to free
	 * it here.
	 */
	if (ofs)
		ovl_free_fs(ofs);

	if (ctx)
		ovl_fs_context_free(ctx);
}

static int ovl_reconfigure(struct fs_context *fc)
{
	struct super_block *sb = fc->root->d_sb;
	struct ovl_fs *ofs = OVL_FS(sb);
	struct super_block *upper_sb;
	int ret = 0;

	if (!(fc->sb_flags & SB_RDONLY) && ovl_force_readonly(ofs))
		return -EROFS;

	if (fc->sb_flags & SB_RDONLY && !sb_rdonly(sb)) {
		upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
		if (ovl_should_sync(ofs)) {
			down_read(&upper_sb->s_umount);
			ret = sync_filesystem(upper_sb);
			up_read(&upper_sb->s_umount);
		}
	}

	return ret;
}

static const struct fs_context_operations ovl_context_ops = {
	.parse_param = ovl_parse_param,
	.get_tree    = ovl_get_tree,
	.reconfigure = ovl_reconfigure,
	.free        = ovl_free,
};

/*
 * This is called during fsopen() and will record the user namespace of
 * the caller in fc->user_ns since we've raised FS_USERNS_MOUNT. We'll
 * need it when we actually create the superblock to verify that the
 * process creating the superblock is in the same user namespace as
 * process that called fsopen().
 */
int ovl_init_fs_context(struct fs_context *fc)
{
	struct ovl_fs_context *ctx;
	struct ovl_fs *ofs;

	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
	if (!ctx)
		return -ENOMEM;

	/*
	 * By default we allocate for three lower layers. It's likely
	 * that it'll cover most users.
	 */
	ctx->lower = kmalloc_array(3, sizeof(*ctx->lower), GFP_KERNEL_ACCOUNT);
	if (!ctx->lower)
		goto out_err;
	ctx->capacity = 3;

	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
	if (!ofs)
		goto out_err;

	ofs->config.redirect_mode	= ovl_redirect_mode_def();
	ofs->config.index		= ovl_index_def;
	ofs->config.uuid		= ovl_uuid_def();
	ofs->config.nfs_export		= ovl_nfs_export_def;
	ofs->config.xino		= ovl_xino_def();
	ofs->config.metacopy		= ovl_metacopy_def;

	fc->s_fs_info		= ofs;
	fc->fs_private		= ctx;
	fc->ops			= &ovl_context_ops;
	return 0;

out_err:
	ovl_fs_context_free(ctx);
	return -ENOMEM;

}

void ovl_free_fs(struct ovl_fs *ofs)
{
	struct vfsmount **mounts;
	unsigned i;

	iput(ofs->workbasedir_trap);
	iput(ofs->indexdir_trap);
	iput(ofs->workdir_trap);
	dput(ofs->whiteout);
	dput(ofs->indexdir);
	dput(ofs->workdir);
	if (ofs->workdir_locked)
		ovl_inuse_unlock(ofs->workbasedir);
	dput(ofs->workbasedir);
	if (ofs->upperdir_locked)
		ovl_inuse_unlock(ovl_upper_mnt(ofs)->mnt_root);

	/* Hack!  Reuse ofs->layers as a vfsmount array before freeing it */
	mounts = (struct vfsmount **) ofs->layers;
	for (i = 0; i < ofs->numlayer; i++) {
		iput(ofs->layers[i].trap);
		mounts[i] = ofs->layers[i].mnt;
		kfree(ofs->layers[i].name);
	}
	kern_unmount_array(mounts, ofs->numlayer);
	kfree(ofs->layers);
	for (i = 0; i < ofs->numfs; i++)
		free_anon_bdev(ofs->fs[i].pseudo_dev);
	kfree(ofs->fs);

	kfree(ofs->config.upperdir);
	kfree(ofs->config.workdir);
	if (ofs->creator_cred)
		put_cred(ofs->creator_cred);
	kfree(ofs);
}

int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
			 struct ovl_config *config)
{
	struct ovl_opt_set set = ctx->set;

	if (ctx->nr_data > 0 && !config->metacopy) {
		pr_err("lower data-only dirs require metacopy support.\n");
		return -EINVAL;
	}

	/* Workdir/index are useless in non-upper mount */
	if (!config->upperdir) {
		if (config->workdir) {
			pr_info("option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
				config->workdir);
			kfree(config->workdir);
			config->workdir = NULL;
		}
		if (config->index && set.index) {
			pr_info("option \"index=on\" is useless in a non-upper mount, ignore\n");
			set.index = false;
		}
		config->index = false;
	}

	if (!config->upperdir && config->ovl_volatile) {
		pr_info("option \"volatile\" is meaningless in a non-upper mount, ignoring it.\n");
		config->ovl_volatile = false;
	}

	if (!config->upperdir && config->uuid == OVL_UUID_ON) {
		pr_info("option \"uuid=on\" requires an upper fs, falling back to uuid=null.\n");
		config->uuid = OVL_UUID_NULL;
	}

	/* Resolve verity -> metacopy dependency */
	if (config->verity_mode && !config->metacopy) {
		/* Don't allow explicit specified conflicting combinations */
		if (set.metacopy) {
			pr_err("conflicting options: metacopy=off,verity=%s\n",
			       ovl_verity_mode(config));
			return -EINVAL;
		}
		/* Otherwise automatically enable metacopy. */
		config->metacopy = true;
	}

	/*
	 * This is to make the logic below simpler.  It doesn't make any other
	 * difference, since redirect_dir=on is only used for upper.
	 */
	if (!config->upperdir && config->redirect_mode == OVL_REDIRECT_FOLLOW)
		config->redirect_mode = OVL_REDIRECT_ON;

	/* Resolve verity -> metacopy -> redirect_dir dependency */
	if (config->metacopy && config->redirect_mode != OVL_REDIRECT_ON) {
		if (set.metacopy && set.redirect) {
			pr_err("conflicting options: metacopy=on,redirect_dir=%s\n",
			       ovl_redirect_mode(config));
			return -EINVAL;
		}
		if (config->verity_mode && set.redirect) {
			pr_err("conflicting options: verity=%s,redirect_dir=%s\n",
			       ovl_verity_mode(config), ovl_redirect_mode(config));
			return -EINVAL;
		}
		if (set.redirect) {
			/*
			 * There was an explicit redirect_dir=... that resulted
			 * in this conflict.
			 */
			pr_info("disabling metacopy due to redirect_dir=%s\n",
				ovl_redirect_mode(config));
			config->metacopy = false;
		} else {
			/* Automatically enable redirect otherwise. */
			config->redirect_mode = OVL_REDIRECT_ON;
		}
	}

	/* Resolve nfs_export -> index dependency */
	if (config->nfs_export && !config->index) {
		if (!config->upperdir &&
		    config->redirect_mode != OVL_REDIRECT_NOFOLLOW) {
			pr_info("NFS export requires \"redirect_dir=nofollow\" on non-upper mount, falling back to nfs_export=off.\n");
			config->nfs_export = false;
		} else if (set.nfs_export && set.index) {
			pr_err("conflicting options: nfs_export=on,index=off\n");
			return -EINVAL;
		} else if (set.index) {
			/*
			 * There was an explicit index=off that resulted
			 * in this conflict.
			 */
			pr_info("disabling nfs_export due to index=off\n");
			config->nfs_export = false;
		} else {
			/* Automatically enable index otherwise. */
			config->index = true;
		}
	}

	/* Resolve nfs_export -> !metacopy && !verity dependency */
	if (config->nfs_export && config->metacopy) {
		if (set.nfs_export && set.metacopy) {
			pr_err("conflicting options: nfs_export=on,metacopy=on\n");
			return -EINVAL;
		}
		if (set.metacopy) {
			/*
			 * There was an explicit metacopy=on that resulted
			 * in this conflict.
			 */
			pr_info("disabling nfs_export due to metacopy=on\n");
			config->nfs_export = false;
		} else if (config->verity_mode) {
			/*
			 * There was an explicit verity=.. that resulted
			 * in this conflict.
			 */
			pr_info("disabling nfs_export due to verity=%s\n",
				ovl_verity_mode(config));
			config->nfs_export = false;
		} else {
			/*
			 * There was an explicit nfs_export=on that resulted
			 * in this conflict.
			 */
			pr_info("disabling metacopy due to nfs_export=on\n");
			config->metacopy = false;
		}
	}


	/* Resolve userxattr -> !redirect && !metacopy && !verity dependency */
	if (config->userxattr) {
		if (set.redirect &&
		    config->redirect_mode != OVL_REDIRECT_NOFOLLOW) {
			pr_err("conflicting options: userxattr,redirect_dir=%s\n",
			       ovl_redirect_mode(config));
			return -EINVAL;
		}
		if (config->metacopy && set.metacopy) {
			pr_err("conflicting options: userxattr,metacopy=on\n");
			return -EINVAL;
		}
		if (config->verity_mode) {
			pr_err("conflicting options: userxattr,verity=%s\n",
			       ovl_verity_mode(config));
			return -EINVAL;
		}
		/*
		 * Silently disable default setting of redirect and metacopy.
		 * This shall be the default in the future as well: these
		 * options must be explicitly enabled if used together with
		 * userxattr.
		 */
		config->redirect_mode = OVL_REDIRECT_NOFOLLOW;
		config->metacopy = false;
	}

	return 0;
}

/**
 * ovl_show_options
 * @m: the seq_file handle
 * @dentry: The dentry to query
 *
 * Prints the mount options for a given superblock.
 * Returns zero; does not fail.
 */
int ovl_show_options(struct seq_file *m, struct dentry *dentry)
{
	struct super_block *sb = dentry->d_sb;
	struct ovl_fs *ofs = OVL_FS(sb);
	size_t nr, nr_merged_lower = ofs->numlayer - ofs->numdatalayer;
	const struct ovl_layer *data_layers = &ofs->layers[nr_merged_lower];

	/* ofs->layers[0] is the upper layer */
	seq_printf(m, ",lowerdir=%s", ofs->layers[1].name);
	/* dump regular lower layers */
	for (nr = 2; nr < nr_merged_lower; nr++)
		seq_printf(m, ":%s", ofs->layers[nr].name);
	/* dump data lower layers */
	for (nr = 0; nr < ofs->numdatalayer; nr++)
		seq_printf(m, "::%s", data_layers[nr].name);
	if (ofs->config.upperdir) {
		seq_show_option(m, "upperdir", ofs->config.upperdir);
		seq_show_option(m, "workdir", ofs->config.workdir);
	}
	if (ofs->config.default_permissions)
		seq_puts(m, ",default_permissions");
	if (ofs->config.redirect_mode != ovl_redirect_mode_def())
		seq_printf(m, ",redirect_dir=%s",
			   ovl_redirect_mode(&ofs->config));
	if (ofs->config.index != ovl_index_def)
		seq_printf(m, ",index=%s", ofs->config.index ? "on" : "off");
	if (ofs->config.uuid != ovl_uuid_def())
		seq_printf(m, ",uuid=%s", ovl_uuid_mode(&ofs->config));
	if (ofs->config.nfs_export != ovl_nfs_export_def)
		seq_printf(m, ",nfs_export=%s", ofs->config.nfs_export ?
						"on" : "off");
	if (ofs->config.xino != ovl_xino_def() && !ovl_same_fs(ofs))
		seq_printf(m, ",xino=%s", ovl_xino_mode(&ofs->config));
	if (ofs->config.metacopy != ovl_metacopy_def)
		seq_printf(m, ",metacopy=%s",
			   ofs->config.metacopy ? "on" : "off");
	if (ofs->config.ovl_volatile)
		seq_puts(m, ",volatile");
	if (ofs->config.userxattr)
		seq_puts(m, ",userxattr");
	if (ofs->config.verity_mode != ovl_verity_mode_def())
		seq_printf(m, ",verity=%s",
			   ovl_verity_mode(&ofs->config));
	return 0;
}