[PATCH v2 0/2] ovl: port to new mount api & updated layer parsing

[PATCH v2 0/2] ovl: port to new mount api & updated layer parsing

[Christian Brauner]

Hey everyone,

This ports overlayfs to the new mount api and modifies layer parsing to
allow for additive layer specification via fsconfig().

I'm not sure if I need to rebase the changes on top of Amir's lazy
lookup. If so, please let me know!

Christian

---
Changes in v2:
- Split into two patches. First patch ports to new mount api without changing
  layer parsing. Second patch implements new layer parsing.
- Move layer parsing into a separate file.
- Link to v1: https://lore.kernel.org/r/20230605-fs-overlayfs-mount_api-v1-1-a8d78c3fbeaf@kernel.org

---



---
base-commit: 9561de3a55bed6bdd44a12820ba81ec416e705a7
change-id: 20230605-fs-overlayfs-mount_api-20ea8b04eff4

[PATCH v2 1/2] ovl: port to new mount api

[Christian Brauner]

We recently ported util-linux to the new mount api. Now the mount(8)
tool will by default use the new mount api. While trying hard to fall
back to the old mount api gracefully there are still cases where we run
into issues that are difficult to handle nicely.

Now with mount(8) and libmount supporting the new mount api I expect an
increase in the number of bug reports and issues we're going to see with
filesystems that don't yet support the new mount api. So it's time we
rectify this.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/overlayfs/super.c | 515 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 279 insertions(+), 236 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f97ad8b40dbb..ceaf05743f45 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -16,6 +16,8 @@
 #include <linux/posix_acl_xattr.h>
 #include <linux/exportfs.h>
 #include <linux/file.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
 #include "overlayfs.h"
 
 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
@@ -67,6 +69,59 @@ 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_volatile,
+};
+
+static const struct constant_table ovl_parameter_bool[] = {
+	{ "on",		true  },
+	{ "off",	false },
+	{}
+};
+
+static const struct constant_table ovl_parameter_xino[] = {
+	{ "on",		OVL_XINO_ON   },
+	{ "off",	OVL_XINO_OFF  },
+	{ "auto",	OVL_XINO_AUTO },
+	{}
+};
+
+static const struct fs_parameter_spec ovl_parameter_spec[] = {
+	fsparam_string("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_bool),
+	fsparam_enum("index",               Opt_index, ovl_parameter_bool),
+	fsparam_enum("uuid",                Opt_uuid, ovl_parameter_bool),
+	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_flag("volatile",            Opt_volatile),
+	{}
+};
+
+#define OVL_METACOPY_SET	BIT(0)
+#define OVL_REDIRECT_SET	BIT(1)
+#define OVL_NFS_EXPORT_SET	BIT(2)
+#define OVL_INDEX_SET		BIT(3)
+
+struct ovl_fs_context {
+	u8 set;
+};
+
 static void ovl_dentry_release(struct dentry *dentry)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;
@@ -394,27 +449,6 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 	return 0;
 }
 
-static int ovl_remount(struct super_block *sb, int *flags, char *data)
-{
-	struct ovl_fs *ofs = sb->s_fs_info;
-	struct super_block *upper_sb;
-	int ret = 0;
-
-	if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
-		return -EROFS;
-
-	if (*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 super_operations ovl_super_operations = {
 	.alloc_inode	= ovl_alloc_inode,
 	.free_inode	= ovl_free_inode,
@@ -424,76 +458,8 @@ static const struct super_operations ovl_super_operations = {
 	.sync_fs	= ovl_sync_fs,
 	.statfs		= ovl_statfs,
 	.show_options	= ovl_show_options,
-	.remount_fs	= ovl_remount,
-};
-
-enum {
-	OPT_LOWERDIR,
-	OPT_UPPERDIR,
-	OPT_WORKDIR,
-	OPT_DEFAULT_PERMISSIONS,
-	OPT_REDIRECT_DIR,
-	OPT_INDEX_ON,
-	OPT_INDEX_OFF,
-	OPT_UUID_ON,
-	OPT_UUID_OFF,
-	OPT_NFS_EXPORT_ON,
-	OPT_USERXATTR,
-	OPT_NFS_EXPORT_OFF,
-	OPT_XINO_ON,
-	OPT_XINO_OFF,
-	OPT_XINO_AUTO,
-	OPT_METACOPY_ON,
-	OPT_METACOPY_OFF,
-	OPT_VOLATILE,
-	OPT_ERR,
-};
-
-static const match_table_t ovl_tokens = {
-	{OPT_LOWERDIR,			"lowerdir=%s"},
-	{OPT_UPPERDIR,			"upperdir=%s"},
-	{OPT_WORKDIR,			"workdir=%s"},
-	{OPT_DEFAULT_PERMISSIONS,	"default_permissions"},
-	{OPT_REDIRECT_DIR,		"redirect_dir=%s"},
-	{OPT_INDEX_ON,			"index=on"},
-	{OPT_INDEX_OFF,			"index=off"},
-	{OPT_USERXATTR,			"userxattr"},
-	{OPT_UUID_ON,			"uuid=on"},
-	{OPT_UUID_OFF,			"uuid=off"},
-	{OPT_NFS_EXPORT_ON,		"nfs_export=on"},
-	{OPT_NFS_EXPORT_OFF,		"nfs_export=off"},
-	{OPT_XINO_ON,			"xino=on"},
-	{OPT_XINO_OFF,			"xino=off"},
-	{OPT_XINO_AUTO,			"xino=auto"},
-	{OPT_METACOPY_ON,		"metacopy=on"},
-	{OPT_METACOPY_OFF,		"metacopy=off"},
-	{OPT_VOLATILE,			"volatile"},
-	{OPT_ERR,			NULL}
 };
 
-static char *ovl_next_opt(char **s)
-{
-	char *sbegin = *s;
-	char *p;
-
-	if (sbegin == NULL)
-		return NULL;
-
-	for (p = sbegin; *p; p++) {
-		if (*p == '\\') {
-			p++;
-			if (!*p)
-				break;
-		} else if (*p == ',') {
-			*p = '\0';
-			*s = p + 1;
-			return sbegin;
-		}
-	}
-	*s = NULL;
-	return sbegin;
-}
-
 static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
 {
 	if (strcmp(mode, "on") == 0) {
@@ -517,123 +483,14 @@ static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
 	return 0;
 }
 
-static int ovl_parse_opt(char *opt, struct ovl_config *config)
+static int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
+				struct ovl_config *config)
 {
-	char *p;
 	int err;
-	bool metacopy_opt = false, redirect_opt = false;
-	bool nfs_export_opt = false, index_opt = false;
-
-	config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
-	if (!config->redirect_mode)
-		return -ENOMEM;
-
-	while ((p = ovl_next_opt(&opt)) != NULL) {
-		int token;
-		substring_t args[MAX_OPT_ARGS];
-
-		if (!*p)
-			continue;
-
-		token = match_token(p, ovl_tokens, args);
-		switch (token) {
-		case OPT_UPPERDIR:
-			kfree(config->upperdir);
-			config->upperdir = match_strdup(&args[0]);
-			if (!config->upperdir)
-				return -ENOMEM;
-			break;
-
-		case OPT_LOWERDIR:
-			kfree(config->lowerdir);
-			config->lowerdir = match_strdup(&args[0]);
-			if (!config->lowerdir)
-				return -ENOMEM;
-			break;
-
-		case OPT_WORKDIR:
-			kfree(config->workdir);
-			config->workdir = match_strdup(&args[0]);
-			if (!config->workdir)
-				return -ENOMEM;
-			break;
-
-		case OPT_DEFAULT_PERMISSIONS:
-			config->default_permissions = true;
-			break;
-
-		case OPT_REDIRECT_DIR:
-			kfree(config->redirect_mode);
-			config->redirect_mode = match_strdup(&args[0]);
-			if (!config->redirect_mode)
-				return -ENOMEM;
-			redirect_opt = true;
-			break;
-
-		case OPT_INDEX_ON:
-			config->index = true;
-			index_opt = true;
-			break;
-
-		case OPT_INDEX_OFF:
-			config->index = false;
-			index_opt = true;
-			break;
-
-		case OPT_UUID_ON:
-			config->uuid = true;
-			break;
-
-		case OPT_UUID_OFF:
-			config->uuid = false;
-			break;
-
-		case OPT_NFS_EXPORT_ON:
-			config->nfs_export = true;
-			nfs_export_opt = true;
-			break;
-
-		case OPT_NFS_EXPORT_OFF:
-			config->nfs_export = false;
-			nfs_export_opt = true;
-			break;
-
-		case OPT_XINO_ON:
-			config->xino = OVL_XINO_ON;
-			break;
-
-		case OPT_XINO_OFF:
-			config->xino = OVL_XINO_OFF;
-			break;
-
-		case OPT_XINO_AUTO:
-			config->xino = OVL_XINO_AUTO;
-			break;
-
-		case OPT_METACOPY_ON:
-			config->metacopy = true;
-			metacopy_opt = true;
-			break;
-
-		case OPT_METACOPY_OFF:
-			config->metacopy = false;
-			metacopy_opt = true;
-			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",
-					p);
-			return -EINVAL;
-		}
-	}
+	bool metacopy_opt = ctx->set & OVL_METACOPY_SET,
+	     redirect_opt = ctx->set & OVL_REDIRECT_SET;
+	bool nfs_export_opt = ctx->set & OVL_NFS_EXPORT_SET,
+	     index_opt = ctx->set & OVL_INDEX_SET;
 
 	/* Workdir/index are useless in non-upper mount */
 	if (!config->upperdir) {
@@ -1882,12 +1739,143 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 	return root;
 }
 
-static int ovl_fill_super(struct super_block *sb, void *data, int silent)
+static int ovl_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
-	struct path upperpath = { };
+	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;
+	struct path path;
+	char *dup;
+	int opt;
+	char *sval;
+
+	/*
+	 * 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->purpose == FS_CONTEXT_FOR_RECONFIGURE)
+		return 0;
+
+	opt = fs_parse(fc, ovl_parameter_spec, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_lowerdir:
+		dup = kstrdup(param->string, GFP_KERNEL);
+		if (!dup) {
+			path_put(&path);
+			err = -ENOMEM;
+			break;
+		}
+
+		kfree(config->lowerdir);
+		config->lowerdir = dup;
+		break;
+	case Opt_upperdir:
+		dup = kstrdup(param->string, GFP_KERNEL);
+		if (!dup) {
+			path_put(&path);
+			err = -ENOMEM;
+			break;
+		}
+
+		kfree(config->upperdir);
+		config->upperdir = dup;
+		break;
+	case Opt_workdir:
+		dup = kstrdup(param->string, GFP_KERNEL);
+		if (!dup) {
+			path_put(&path);
+			err = -ENOMEM;
+			break;
+		}
+
+		kfree(config->workdir);
+		config->workdir = dup;
+		break;
+	case Opt_default_permissions:
+		config->default_permissions = true;
+		break;
+	case Opt_index:
+		config->index = result.uint_32;
+		ctx->set |= OVL_INDEX_SET;
+		break;
+	case Opt_uuid:
+		config->uuid = result.uint_32;
+		break;
+	case Opt_nfs_export:
+		config->nfs_export = result.uint_32;
+		ctx->set |= OVL_NFS_EXPORT_SET;
+		break;
+	case Opt_metacopy:
+		config->metacopy = result.uint_32;
+		ctx->set |= OVL_METACOPY_SET;
+		break;
+	case Opt_userxattr:
+		config->userxattr = true;
+		break;
+	case Opt_volatile:
+		config->ovl_volatile = true;
+		break;
+	case Opt_xino:
+		config->xino = result.uint_32;
+		break;
+	case Opt_redirect_dir:
+		if (result.uint_32 == true)
+			sval = kstrdup("on", GFP_KERNEL);
+		else
+			sval = kstrdup("off", GFP_KERNEL);
+		if (!sval) {
+			err = -ENOMEM;
+			break;
+		}
+
+		kfree(config->redirect_mode);
+		config->redirect_mode = sval;
+		ctx->set |= OVL_REDIRECT_SET;
+		break;
+	default:
+		pr_err("unrecognized mount option \"%s\" or missing value\n", param->key);
+		return -EINVAL;
+	}
+
+	return err;
+}
+
+
+static int ovl_reconfigure(struct fs_context *fc)
+{
+	struct super_block *sb = fc->root->d_sb;
+	struct ovl_fs *ofs = sb->s_fs_info;
+	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 int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct ovl_fs_context *ctx = fc->fs_private;
+	struct path upperpath = {};
 	struct dentry *root_dentry;
 	struct ovl_entry *oe;
-	struct ovl_fs *ofs;
 	struct ovl_layer *layers;
 	struct cred *cred;
 	char *splitlower = NULL;
@@ -1895,36 +1883,24 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	int err;
 
 	err = -EIO;
-	if (WARN_ON(sb->s_user_ns != current_user_ns()))
-		goto out;
+	if (WARN_ON(fc->user_ns != current_user_ns()))
+		goto out_err;
 
+	ofs->share_whiteout = true;
 	sb->s_d_op = &ovl_dentry_operations;
 
-	err = -ENOMEM;
-	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
-	if (!ofs)
-		goto out;
-
 	err = -ENOMEM;
 	ofs->creator_cred = cred = prepare_creds();
 	if (!cred)
 		goto out_err;
 
-	/* Is there a reason anyone would want not to share whiteouts? */
-	ofs->share_whiteout = true;
-
-	ofs->config.index = ovl_index_def;
-	ofs->config.uuid = true;
-	ofs->config.nfs_export = ovl_nfs_export_def;
-	ofs->config.xino = ovl_xino_def();
-	ofs->config.metacopy = ovl_metacopy_def;
-	err = ovl_parse_opt((char *) data, &ofs->config);
+	err = ovl_fs_params_verify(ctx, &ofs->config);
 	if (err)
 		goto out_err;
 
 	err = -EINVAL;
 	if (!ofs->config.lowerdir) {
-		if (!silent)
+		if (fc->sb_flags & SB_SILENT)
 			pr_err("missing 'lowerdir'\n");
 		goto out_err;
 	}
@@ -2070,25 +2046,92 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	ovl_entry_stack_free(oe);
 	kfree(oe);
 out_err:
-	kfree(splitlower);
-	path_put(&upperpath);
-	ovl_free_fs(ofs);
-out:
 	return err;
 }
 
-static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
-				const char *dev_name, void *raw_data)
+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)
 {
-	return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
+	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 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().
+ */
+static int ovl_init_fs_context(struct fs_context *fc)
+{
+	struct ovl_fs_context *ctx = NULL;
+	struct ovl_fs *ofs = NULL;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
+	if (!ctx)
+		goto out_err;
+
+	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
+	if (!ofs)
+		goto out_err;
+
+	ofs->config.redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
+	if (!ofs->config.redirect_mode)
+		goto out_err;
+
+	ofs->config.index	= ovl_index_def;
+	ofs->config.uuid	= true;
+	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);
+	ovl_free_fs(ofs);
+	return -ENOMEM;
 }
 
 static struct file_system_type ovl_fs_type = {
-	.owner		= THIS_MODULE,
-	.name		= "overlay",
-	.fs_flags	= FS_USERNS_MOUNT,
-	.mount		= ovl_mount,
-	.kill_sb	= kill_anon_super,
+	.owner			= THIS_MODULE,
+	.name			= "overlay",
+	.init_fs_context	= ovl_init_fs_context,
+	.parameters		= ovl_parameter_spec,
+	.fs_flags		= FS_USERNS_MOUNT,
+	.kill_sb		= kill_anon_super,
 };
 MODULE_ALIAS_FS("overlay");
 

-- 
2.34.1

Re: [PATCH v2 1/2] ovl: port to new mount api

[Colin Walters]

Cool work.  It will be interesting to do some performance testing on what does it actually look like to create ~500 or whatever overlayfs layers now that we can.

On Fri, Jun 9, 2023, at 11:41 AM, Christian Brauner wrote:
> 
> +static int ovl_init_fs_context(struct fs_context *fc)
> +{
> +	struct ovl_fs_context *ctx = NULL;
> +	struct ovl_fs *ofs = NULL;
> +
> +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
> +	if (!ctx)
> +		goto out_err;

It looks to me like in this case, ofs will be NULL, then:

> +out_err:
> +	ovl_fs_context_free(ctx);
> +	ovl_free_fs(ofs);

And then we'll jump here and `ovl_free_fs` is not NULL safe.

I think the previous code was correct here as it just jumped directly to "out:".


(I've always wondered why there's no usage of __attribute__((cleanup)) in kernel code and in our userspace code doing that we have the free functions be no-ops on NULL which systematically avoids these bugs, but then again maybe the real fix is Rust ;) )

Re: [PATCH v2 1/2] ovl: port to new mount api

[Christian Brauner]

On Fri, Jun 09, 2023 at 12:09:08PM -0400, Colin Walters wrote:
> Cool work.  It will be interesting to do some performance testing on what does it actually look like to create ~500 or whatever overlayfs layers now that we can.
> 
> On Fri, Jun 9, 2023, at 11:41 AM, Christian Brauner wrote:
> > 
> > +static int ovl_init_fs_context(struct fs_context *fc)
> > +{
> > +	struct ovl_fs_context *ctx = NULL;
> > +	struct ovl_fs *ofs = NULL;
> > +
> > +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
> > +	if (!ctx)
> > +		goto out_err;
> 
> It looks to me like in this case, ofs will be NULL, then:
> 
> > +out_err:
> > +	ovl_fs_context_free(ctx);
> > +	ovl_free_fs(ofs);
> 
> And then we'll jump here and `ovl_free_fs` is not NULL safe.
> 
> I think the previous code was correct here as it just jumped directly to "out:".

Good catch, thanks!

> 
> 
> (I've always wondered why there's no usage of __attribute__((cleanup))
> in kernel code and in our userspace code doing that we have the free
> functions be no-ops on NULL which systematically avoids these bugs,
> but then again maybe the real fix is Rust ;) )

I have talked about this before and actually do have a PoC patch in my
tree somewhere I never bothered to send it because it didn't feel like I
had the time for the flamewar+bikeshed that would end up
happening... Maybe I should just try.

Re: [PATCH v2 1/2] ovl: port to new mount api

[Amir Goldstein]

On Fri, Jun 9, 2023 at 6:42 PM Christian Brauner <brauner@kernel.org> wrote:
>
> We recently ported util-linux to the new mount api. Now the mount(8)
> tool will by default use the new mount api. While trying hard to fall
> back to the old mount api gracefully there are still cases where we run
> into issues that are difficult to handle nicely.
>
> Now with mount(8) and libmount supporting the new mount api I expect an
> increase in the number of bug reports and issues we're going to see with
> filesystems that don't yet support the new mount api. So it's time we
> rectify this.
>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> ---
>  fs/overlayfs/super.c | 515 ++++++++++++++++++++++++++++-----------------------
>  1 file changed, 279 insertions(+), 236 deletions(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index f97ad8b40dbb..ceaf05743f45 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -16,6 +16,8 @@
>  #include <linux/posix_acl_xattr.h>
>  #include <linux/exportfs.h>
>  #include <linux/file.h>
> +#include <linux/fs_context.h>
> +#include <linux/fs_parser.h>
>  #include "overlayfs.h"
>
>  MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
> @@ -67,6 +69,59 @@ 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_volatile,
> +};
> +
> +static const struct constant_table ovl_parameter_bool[] = {
> +       { "on",         true  },
> +       { "off",        false },
> +       {}
> +};
> +
> +static const struct constant_table ovl_parameter_xino[] = {
> +       { "on",         OVL_XINO_ON   },
> +       { "off",        OVL_XINO_OFF  },
> +       { "auto",       OVL_XINO_AUTO },
> +       {}
> +};
> +
> +static const struct fs_parameter_spec ovl_parameter_spec[] = {
> +       fsparam_string("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_bool),
> +       fsparam_enum("index",               Opt_index, ovl_parameter_bool),
> +       fsparam_enum("uuid",                Opt_uuid, ovl_parameter_bool),
> +       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_flag("volatile",            Opt_volatile),
> +       {}
> +};
> +
> +#define OVL_METACOPY_SET       BIT(0)
> +#define OVL_REDIRECT_SET       BIT(1)
> +#define OVL_NFS_EXPORT_SET     BIT(2)
> +#define OVL_INDEX_SET          BIT(3)
> +
> +struct ovl_fs_context {
> +       u8 set;
> +};
> +
>  static void ovl_dentry_release(struct dentry *dentry)
>  {
>         struct ovl_entry *oe = dentry->d_fsdata;
> @@ -394,27 +449,6 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
>         return 0;
>  }
>
> -static int ovl_remount(struct super_block *sb, int *flags, char *data)
> -{
> -       struct ovl_fs *ofs = sb->s_fs_info;
> -       struct super_block *upper_sb;
> -       int ret = 0;
> -
> -       if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
> -               return -EROFS;
> -
> -       if (*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 super_operations ovl_super_operations = {
>         .alloc_inode    = ovl_alloc_inode,
>         .free_inode     = ovl_free_inode,
> @@ -424,76 +458,8 @@ static const struct super_operations ovl_super_operations = {
>         .sync_fs        = ovl_sync_fs,
>         .statfs         = ovl_statfs,
>         .show_options   = ovl_show_options,
> -       .remount_fs     = ovl_remount,
> -};
> -
> -enum {
> -       OPT_LOWERDIR,
> -       OPT_UPPERDIR,
> -       OPT_WORKDIR,
> -       OPT_DEFAULT_PERMISSIONS,
> -       OPT_REDIRECT_DIR,
> -       OPT_INDEX_ON,
> -       OPT_INDEX_OFF,
> -       OPT_UUID_ON,
> -       OPT_UUID_OFF,
> -       OPT_NFS_EXPORT_ON,
> -       OPT_USERXATTR,
> -       OPT_NFS_EXPORT_OFF,
> -       OPT_XINO_ON,
> -       OPT_XINO_OFF,
> -       OPT_XINO_AUTO,
> -       OPT_METACOPY_ON,
> -       OPT_METACOPY_OFF,
> -       OPT_VOLATILE,
> -       OPT_ERR,
> -};
> -
> -static const match_table_t ovl_tokens = {
> -       {OPT_LOWERDIR,                  "lowerdir=%s"},
> -       {OPT_UPPERDIR,                  "upperdir=%s"},
> -       {OPT_WORKDIR,                   "workdir=%s"},
> -       {OPT_DEFAULT_PERMISSIONS,       "default_permissions"},
> -       {OPT_REDIRECT_DIR,              "redirect_dir=%s"},
> -       {OPT_INDEX_ON,                  "index=on"},
> -       {OPT_INDEX_OFF,                 "index=off"},
> -       {OPT_USERXATTR,                 "userxattr"},
> -       {OPT_UUID_ON,                   "uuid=on"},
> -       {OPT_UUID_OFF,                  "uuid=off"},
> -       {OPT_NFS_EXPORT_ON,             "nfs_export=on"},
> -       {OPT_NFS_EXPORT_OFF,            "nfs_export=off"},
> -       {OPT_XINO_ON,                   "xino=on"},
> -       {OPT_XINO_OFF,                  "xino=off"},
> -       {OPT_XINO_AUTO,                 "xino=auto"},
> -       {OPT_METACOPY_ON,               "metacopy=on"},
> -       {OPT_METACOPY_OFF,              "metacopy=off"},
> -       {OPT_VOLATILE,                  "volatile"},
> -       {OPT_ERR,                       NULL}
>  };
>
> -static char *ovl_next_opt(char **s)
> -{
> -       char *sbegin = *s;
> -       char *p;
> -
> -       if (sbegin == NULL)
> -               return NULL;
> -
> -       for (p = sbegin; *p; p++) {
> -               if (*p == '\\') {
> -                       p++;
> -                       if (!*p)
> -                               break;
> -               } else if (*p == ',') {
> -                       *p = '\0';
> -                       *s = p + 1;
> -                       return sbegin;
> -               }
> -       }
> -       *s = NULL;
> -       return sbegin;
> -}
> -
>  static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
>  {
>         if (strcmp(mode, "on") == 0) {
> @@ -517,123 +483,14 @@ static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
>         return 0;
>  }
>
> -static int ovl_parse_opt(char *opt, struct ovl_config *config)
> +static int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> +                               struct ovl_config *config)
>  {
> -       char *p;
>         int err;
> -       bool metacopy_opt = false, redirect_opt = false;
> -       bool nfs_export_opt = false, index_opt = false;
> -
> -       config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
> -       if (!config->redirect_mode)
> -               return -ENOMEM;
> -
> -       while ((p = ovl_next_opt(&opt)) != NULL) {
> -               int token;
> -               substring_t args[MAX_OPT_ARGS];
> -
> -               if (!*p)
> -                       continue;
> -
> -               token = match_token(p, ovl_tokens, args);
> -               switch (token) {
> -               case OPT_UPPERDIR:
> -                       kfree(config->upperdir);
> -                       config->upperdir = match_strdup(&args[0]);
> -                       if (!config->upperdir)
> -                               return -ENOMEM;
> -                       break;
> -
> -               case OPT_LOWERDIR:
> -                       kfree(config->lowerdir);
> -                       config->lowerdir = match_strdup(&args[0]);
> -                       if (!config->lowerdir)
> -                               return -ENOMEM;
> -                       break;
> -
> -               case OPT_WORKDIR:
> -                       kfree(config->workdir);
> -                       config->workdir = match_strdup(&args[0]);
> -                       if (!config->workdir)
> -                               return -ENOMEM;
> -                       break;
> -
> -               case OPT_DEFAULT_PERMISSIONS:
> -                       config->default_permissions = true;
> -                       break;
> -
> -               case OPT_REDIRECT_DIR:
> -                       kfree(config->redirect_mode);
> -                       config->redirect_mode = match_strdup(&args[0]);
> -                       if (!config->redirect_mode)
> -                               return -ENOMEM;
> -                       redirect_opt = true;
> -                       break;
> -
> -               case OPT_INDEX_ON:
> -                       config->index = true;
> -                       index_opt = true;
> -                       break;
> -
> -               case OPT_INDEX_OFF:
> -                       config->index = false;
> -                       index_opt = true;
> -                       break;
> -
> -               case OPT_UUID_ON:
> -                       config->uuid = true;
> -                       break;
> -
> -               case OPT_UUID_OFF:
> -                       config->uuid = false;
> -                       break;
> -
> -               case OPT_NFS_EXPORT_ON:
> -                       config->nfs_export = true;
> -                       nfs_export_opt = true;
> -                       break;
> -
> -               case OPT_NFS_EXPORT_OFF:
> -                       config->nfs_export = false;
> -                       nfs_export_opt = true;
> -                       break;
> -
> -               case OPT_XINO_ON:
> -                       config->xino = OVL_XINO_ON;
> -                       break;
> -
> -               case OPT_XINO_OFF:
> -                       config->xino = OVL_XINO_OFF;
> -                       break;
> -
> -               case OPT_XINO_AUTO:
> -                       config->xino = OVL_XINO_AUTO;
> -                       break;
> -
> -               case OPT_METACOPY_ON:
> -                       config->metacopy = true;
> -                       metacopy_opt = true;
> -                       break;
> -
> -               case OPT_METACOPY_OFF:
> -                       config->metacopy = false;
> -                       metacopy_opt = true;
> -                       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",
> -                                       p);
> -                       return -EINVAL;
> -               }
> -       }
> +       bool metacopy_opt = ctx->set & OVL_METACOPY_SET,
> +            redirect_opt = ctx->set & OVL_REDIRECT_SET;
> +       bool nfs_export_opt = ctx->set & OVL_NFS_EXPORT_SET,
> +            index_opt = ctx->set & OVL_INDEX_SET;

Nit: please split lines here.

>
>         /* Workdir/index are useless in non-upper mount */
>         if (!config->upperdir) {
> @@ -1882,12 +1739,143 @@ static struct dentry *ovl_get_root(struct super_block *sb,
>         return root;
>  }
>
> -static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> +static int ovl_parse_param(struct fs_context *fc, struct fs_parameter *param)
>  {
> -       struct path upperpath = { };
> +       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;
> +       struct path path;
> +       char *dup;
> +       int opt;
> +       char *sval;
> +
> +       /*
> +        * 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->purpose == FS_CONTEXT_FOR_RECONFIGURE)
> +               return 0;
> +
> +       opt = fs_parse(fc, ovl_parameter_spec, param, &result);
> +       if (opt < 0)
> +               return opt;
> +
> +       switch (opt) {
> +       case Opt_lowerdir:
> +               dup = kstrdup(param->string, GFP_KERNEL);
> +               if (!dup) {
> +                       path_put(&path);
> +                       err = -ENOMEM;
> +                       break;
> +               }
> +
> +               kfree(config->lowerdir);
> +               config->lowerdir = dup;
> +               break;
> +       case Opt_upperdir:
> +               dup = kstrdup(param->string, GFP_KERNEL);
> +               if (!dup) {
> +                       path_put(&path);
> +                       err = -ENOMEM;
> +                       break;
> +               }
> +
> +               kfree(config->upperdir);
> +               config->upperdir = dup;
> +               break;
> +       case Opt_workdir:
> +               dup = kstrdup(param->string, GFP_KERNEL);
> +               if (!dup) {
> +                       path_put(&path);
> +                       err = -ENOMEM;
> +                       break;
> +               }
> +
> +               kfree(config->workdir);
> +               config->workdir = dup;
> +               break;
> +       case Opt_default_permissions:
> +               config->default_permissions = true;
> +               break;
> +       case Opt_index:
> +               config->index = result.uint_32;
> +               ctx->set |= OVL_INDEX_SET;
> +               break;
> +       case Opt_uuid:
> +               config->uuid = result.uint_32;
> +               break;
> +       case Opt_nfs_export:
> +               config->nfs_export = result.uint_32;
> +               ctx->set |= OVL_NFS_EXPORT_SET;
> +               break;
> +       case Opt_metacopy:
> +               config->metacopy = result.uint_32;
> +               ctx->set |= OVL_METACOPY_SET;
> +               break;
> +       case Opt_userxattr:
> +               config->userxattr = true;
> +               break;
> +       case Opt_volatile:
> +               config->ovl_volatile = true;
> +               break;
> +       case Opt_xino:
> +               config->xino = result.uint_32;
> +               break;
> +       case Opt_redirect_dir:
> +               if (result.uint_32 == true)
> +                       sval = kstrdup("on", GFP_KERNEL);
> +               else
> +                       sval = kstrdup("off", GFP_KERNEL);
> +               if (!sval) {
> +                       err = -ENOMEM;
> +                       break;
> +               }
> +
> +               kfree(config->redirect_mode);
> +               config->redirect_mode = sval;
> +               ctx->set |= OVL_REDIRECT_SET;
> +               break;
> +       default:
> +               pr_err("unrecognized mount option \"%s\" or missing value\n", param->key);
> +               return -EINVAL;
> +       }
> +
> +       return err;
> +}


For the end result, all these functions above should be in params.c
I don't mind if you move it with an extra patch at the beginning
Probably easier at the end. Just as long as you do not move
ovl_fs_params_verify() in the same patch that changes half of it.

Thanks,
Amir.

Re: [PATCH v2 1/2] ovl: port to new mount api

[Christian Brauner]

On Fri, Jun 09, 2023 at 10:25:21PM +0300, Amir Goldstein wrote:
> On Fri, Jun 9, 2023 at 6:42 PM Christian Brauner <brauner@kernel.org> wrote:
> >
> > We recently ported util-linux to the new mount api. Now the mount(8)
> > tool will by default use the new mount api. While trying hard to fall
> > back to the old mount api gracefully there are still cases where we run
> > into issues that are difficult to handle nicely.
> >
> > Now with mount(8) and libmount supporting the new mount api I expect an
> > increase in the number of bug reports and issues we're going to see with
> > filesystems that don't yet support the new mount api. So it's time we
> > rectify this.
> >
> > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > ---
> >  fs/overlayfs/super.c | 515 ++++++++++++++++++++++++++++-----------------------
> >  1 file changed, 279 insertions(+), 236 deletions(-)
> >
> > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> > index f97ad8b40dbb..ceaf05743f45 100644
> > --- a/fs/overlayfs/super.c
> > +++ b/fs/overlayfs/super.c
> > @@ -16,6 +16,8 @@
> >  #include <linux/posix_acl_xattr.h>
> >  #include <linux/exportfs.h>
> >  #include <linux/file.h>
> > +#include <linux/fs_context.h>
> > +#include <linux/fs_parser.h>
> >  #include "overlayfs.h"
> >
> >  MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
> > @@ -67,6 +69,59 @@ 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_volatile,
> > +};
> > +
> > +static const struct constant_table ovl_parameter_bool[] = {
> > +       { "on",         true  },
> > +       { "off",        false },
> > +       {}
> > +};
> > +
> > +static const struct constant_table ovl_parameter_xino[] = {
> > +       { "on",         OVL_XINO_ON   },
> > +       { "off",        OVL_XINO_OFF  },
> > +       { "auto",       OVL_XINO_AUTO },
> > +       {}
> > +};
> > +
> > +static const struct fs_parameter_spec ovl_parameter_spec[] = {
> > +       fsparam_string("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_bool),
> > +       fsparam_enum("index",               Opt_index, ovl_parameter_bool),
> > +       fsparam_enum("uuid",                Opt_uuid, ovl_parameter_bool),
> > +       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_flag("volatile",            Opt_volatile),
> > +       {}
> > +};
> > +
> > +#define OVL_METACOPY_SET       BIT(0)
> > +#define OVL_REDIRECT_SET       BIT(1)
> > +#define OVL_NFS_EXPORT_SET     BIT(2)
> > +#define OVL_INDEX_SET          BIT(3)
> > +
> > +struct ovl_fs_context {
> > +       u8 set;
> > +};
> > +
> >  static void ovl_dentry_release(struct dentry *dentry)
> >  {
> >         struct ovl_entry *oe = dentry->d_fsdata;
> > @@ -394,27 +449,6 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
> >         return 0;
> >  }
> >
> > -static int ovl_remount(struct super_block *sb, int *flags, char *data)
> > -{
> > -       struct ovl_fs *ofs = sb->s_fs_info;
> > -       struct super_block *upper_sb;
> > -       int ret = 0;
> > -
> > -       if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
> > -               return -EROFS;
> > -
> > -       if (*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 super_operations ovl_super_operations = {
> >         .alloc_inode    = ovl_alloc_inode,
> >         .free_inode     = ovl_free_inode,
> > @@ -424,76 +458,8 @@ static const struct super_operations ovl_super_operations = {
> >         .sync_fs        = ovl_sync_fs,
> >         .statfs         = ovl_statfs,
> >         .show_options   = ovl_show_options,
> > -       .remount_fs     = ovl_remount,
> > -};
> > -
> > -enum {
> > -       OPT_LOWERDIR,
> > -       OPT_UPPERDIR,
> > -       OPT_WORKDIR,
> > -       OPT_DEFAULT_PERMISSIONS,
> > -       OPT_REDIRECT_DIR,
> > -       OPT_INDEX_ON,
> > -       OPT_INDEX_OFF,
> > -       OPT_UUID_ON,
> > -       OPT_UUID_OFF,
> > -       OPT_NFS_EXPORT_ON,
> > -       OPT_USERXATTR,
> > -       OPT_NFS_EXPORT_OFF,
> > -       OPT_XINO_ON,
> > -       OPT_XINO_OFF,
> > -       OPT_XINO_AUTO,
> > -       OPT_METACOPY_ON,
> > -       OPT_METACOPY_OFF,
> > -       OPT_VOLATILE,
> > -       OPT_ERR,
> > -};
> > -
> > -static const match_table_t ovl_tokens = {
> > -       {OPT_LOWERDIR,                  "lowerdir=%s"},
> > -       {OPT_UPPERDIR,                  "upperdir=%s"},
> > -       {OPT_WORKDIR,                   "workdir=%s"},
> > -       {OPT_DEFAULT_PERMISSIONS,       "default_permissions"},
> > -       {OPT_REDIRECT_DIR,              "redirect_dir=%s"},
> > -       {OPT_INDEX_ON,                  "index=on"},
> > -       {OPT_INDEX_OFF,                 "index=off"},
> > -       {OPT_USERXATTR,                 "userxattr"},
> > -       {OPT_UUID_ON,                   "uuid=on"},
> > -       {OPT_UUID_OFF,                  "uuid=off"},
> > -       {OPT_NFS_EXPORT_ON,             "nfs_export=on"},
> > -       {OPT_NFS_EXPORT_OFF,            "nfs_export=off"},
> > -       {OPT_XINO_ON,                   "xino=on"},
> > -       {OPT_XINO_OFF,                  "xino=off"},
> > -       {OPT_XINO_AUTO,                 "xino=auto"},
> > -       {OPT_METACOPY_ON,               "metacopy=on"},
> > -       {OPT_METACOPY_OFF,              "metacopy=off"},
> > -       {OPT_VOLATILE,                  "volatile"},
> > -       {OPT_ERR,                       NULL}
> >  };
> >
> > -static char *ovl_next_opt(char **s)
> > -{
> > -       char *sbegin = *s;
> > -       char *p;
> > -
> > -       if (sbegin == NULL)
> > -               return NULL;
> > -
> > -       for (p = sbegin; *p; p++) {
> > -               if (*p == '\\') {
> > -                       p++;
> > -                       if (!*p)
> > -                               break;
> > -               } else if (*p == ',') {
> > -                       *p = '\0';
> > -                       *s = p + 1;
> > -                       return sbegin;
> > -               }
> > -       }
> > -       *s = NULL;
> > -       return sbegin;
> > -}
> > -
> >  static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
> >  {
> >         if (strcmp(mode, "on") == 0) {
> > @@ -517,123 +483,14 @@ static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
> >         return 0;
> >  }
> >
> > -static int ovl_parse_opt(char *opt, struct ovl_config *config)
> > +static int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> > +                               struct ovl_config *config)
> >  {
> > -       char *p;
> >         int err;
> > -       bool metacopy_opt = false, redirect_opt = false;
> > -       bool nfs_export_opt = false, index_opt = false;
> > -
> > -       config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
> > -       if (!config->redirect_mode)
> > -               return -ENOMEM;
> > -
> > -       while ((p = ovl_next_opt(&opt)) != NULL) {
> > -               int token;
> > -               substring_t args[MAX_OPT_ARGS];
> > -
> > -               if (!*p)
> > -                       continue;
> > -
> > -               token = match_token(p, ovl_tokens, args);
> > -               switch (token) {
> > -               case OPT_UPPERDIR:
> > -                       kfree(config->upperdir);
> > -                       config->upperdir = match_strdup(&args[0]);
> > -                       if (!config->upperdir)
> > -                               return -ENOMEM;
> > -                       break;
> > -
> > -               case OPT_LOWERDIR:
> > -                       kfree(config->lowerdir);
> > -                       config->lowerdir = match_strdup(&args[0]);
> > -                       if (!config->lowerdir)
> > -                               return -ENOMEM;
> > -                       break;
> > -
> > -               case OPT_WORKDIR:
> > -                       kfree(config->workdir);
> > -                       config->workdir = match_strdup(&args[0]);
> > -                       if (!config->workdir)
> > -                               return -ENOMEM;
> > -                       break;
> > -
> > -               case OPT_DEFAULT_PERMISSIONS:
> > -                       config->default_permissions = true;
> > -                       break;
> > -
> > -               case OPT_REDIRECT_DIR:
> > -                       kfree(config->redirect_mode);
> > -                       config->redirect_mode = match_strdup(&args[0]);
> > -                       if (!config->redirect_mode)
> > -                               return -ENOMEM;
> > -                       redirect_opt = true;
> > -                       break;
> > -
> > -               case OPT_INDEX_ON:
> > -                       config->index = true;
> > -                       index_opt = true;
> > -                       break;
> > -
> > -               case OPT_INDEX_OFF:
> > -                       config->index = false;
> > -                       index_opt = true;
> > -                       break;
> > -
> > -               case OPT_UUID_ON:
> > -                       config->uuid = true;
> > -                       break;
> > -
> > -               case OPT_UUID_OFF:
> > -                       config->uuid = false;
> > -                       break;
> > -
> > -               case OPT_NFS_EXPORT_ON:
> > -                       config->nfs_export = true;
> > -                       nfs_export_opt = true;
> > -                       break;
> > -
> > -               case OPT_NFS_EXPORT_OFF:
> > -                       config->nfs_export = false;
> > -                       nfs_export_opt = true;
> > -                       break;
> > -
> > -               case OPT_XINO_ON:
> > -                       config->xino = OVL_XINO_ON;
> > -                       break;
> > -
> > -               case OPT_XINO_OFF:
> > -                       config->xino = OVL_XINO_OFF;
> > -                       break;
> > -
> > -               case OPT_XINO_AUTO:
> > -                       config->xino = OVL_XINO_AUTO;
> > -                       break;
> > -
> > -               case OPT_METACOPY_ON:
> > -                       config->metacopy = true;
> > -                       metacopy_opt = true;
> > -                       break;
> > -
> > -               case OPT_METACOPY_OFF:
> > -                       config->metacopy = false;
> > -                       metacopy_opt = true;
> > -                       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",
> > -                                       p);
> > -                       return -EINVAL;
> > -               }
> > -       }
> > +       bool metacopy_opt = ctx->set & OVL_METACOPY_SET,
> > +            redirect_opt = ctx->set & OVL_REDIRECT_SET;
> > +       bool nfs_export_opt = ctx->set & OVL_NFS_EXPORT_SET,
> > +            index_opt = ctx->set & OVL_INDEX_SET;
> 
> Nit: please split lines here.
> 
> >
> >         /* Workdir/index are useless in non-upper mount */
> >         if (!config->upperdir) {
> > @@ -1882,12 +1739,143 @@ static struct dentry *ovl_get_root(struct super_block *sb,
> >         return root;
> >  }
> >
> > -static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> > +static int ovl_parse_param(struct fs_context *fc, struct fs_parameter *param)
> >  {
> > -       struct path upperpath = { };
> > +       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;
> > +       struct path path;
> > +       char *dup;
> > +       int opt;
> > +       char *sval;
> > +
> > +       /*
> > +        * 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->purpose == FS_CONTEXT_FOR_RECONFIGURE)
> > +               return 0;
> > +
> > +       opt = fs_parse(fc, ovl_parameter_spec, param, &result);
> > +       if (opt < 0)
> > +               return opt;
> > +
> > +       switch (opt) {
> > +       case Opt_lowerdir:
> > +               dup = kstrdup(param->string, GFP_KERNEL);
> > +               if (!dup) {
> > +                       path_put(&path);
> > +                       err = -ENOMEM;
> > +                       break;
> > +               }
> > +
> > +               kfree(config->lowerdir);
> > +               config->lowerdir = dup;
> > +               break;
> > +       case Opt_upperdir:
> > +               dup = kstrdup(param->string, GFP_KERNEL);
> > +               if (!dup) {
> > +                       path_put(&path);
> > +                       err = -ENOMEM;
> > +                       break;
> > +               }
> > +
> > +               kfree(config->upperdir);
> > +               config->upperdir = dup;
> > +               break;
> > +       case Opt_workdir:
> > +               dup = kstrdup(param->string, GFP_KERNEL);
> > +               if (!dup) {
> > +                       path_put(&path);
> > +                       err = -ENOMEM;
> > +                       break;
> > +               }
> > +
> > +               kfree(config->workdir);
> > +               config->workdir = dup;
> > +               break;
> > +       case Opt_default_permissions:
> > +               config->default_permissions = true;
> > +               break;
> > +       case Opt_index:
> > +               config->index = result.uint_32;
> > +               ctx->set |= OVL_INDEX_SET;
> > +               break;
> > +       case Opt_uuid:
> > +               config->uuid = result.uint_32;
> > +               break;
> > +       case Opt_nfs_export:
> > +               config->nfs_export = result.uint_32;
> > +               ctx->set |= OVL_NFS_EXPORT_SET;
> > +               break;
> > +       case Opt_metacopy:
> > +               config->metacopy = result.uint_32;
> > +               ctx->set |= OVL_METACOPY_SET;
> > +               break;
> > +       case Opt_userxattr:
> > +               config->userxattr = true;
> > +               break;
> > +       case Opt_volatile:
> > +               config->ovl_volatile = true;
> > +               break;
> > +       case Opt_xino:
> > +               config->xino = result.uint_32;
> > +               break;
> > +       case Opt_redirect_dir:
> > +               if (result.uint_32 == true)
> > +                       sval = kstrdup("on", GFP_KERNEL);
> > +               else
> > +                       sval = kstrdup("off", GFP_KERNEL);
> > +               if (!sval) {
> > +                       err = -ENOMEM;
> > +                       break;
> > +               }
> > +
> > +               kfree(config->redirect_mode);
> > +               config->redirect_mode = sval;
> > +               ctx->set |= OVL_REDIRECT_SET;
> > +               break;
> > +       default:
> > +               pr_err("unrecognized mount option \"%s\" or missing value\n", param->key);
> > +               return -EINVAL;
> > +       }
> > +
> > +       return err;
> > +}
> 
> 
> For the end result, all these functions above should be in params.c
> I don't mind if you move it with an extra patch at the beginning
> Probably easier at the end. Just as long as you do not move
> ovl_fs_params_verify() in the same patch that changes half of it.

Ok.

[PATCH v2 2/2] ovl: modify layer parameter parsing

[Christian Brauner]

We ran into issues where mount(8) passed multiple lower layers as one
big string through fsconfig(). But the fsconfig() FSCONFIG_SET_STRING
option is limited to 256 bytes in strndup_user(). While this would be
fixable by extending the fsconfig() buffer I'd rather encourage users to
append layers via multiple fsconfig() calls as the interface allows
nicely for this. This has also been requested as a feature before.

With this port to the new mount api the following will be possible:

        fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", "/lower1", 0);

        /* set upper layer */
        fsconfig(fs_fd, FSCONFIG_SET_STRING, "upperdir", "/upper", 0);

        /* append "/lower2", "/lower3", and "/lower4" */
        fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", ":/lower2:/lower3:/lower4", 0);

        /* turn index feature on */
        fsconfig(fs_fd, FSCONFIG_SET_STRING, "index", "on", 0);

        /* append "/lower5" */
        fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", ":/lower5", 0);

Specifying ':' would have been rejected so this isn't a regression. And
we can't simply use "lowerdir=/lower" to append on top of existing
layers as "lowerdir=/lower,lowerdir=/other-lower" would make
"/other-lower" the only lower layer so we'd break uapi if we changed
this. So the ':' prefix seems a good compromise.

Users can choose to specify multiple layers at once or individual
layers. A layer is appended if it starts with ":". This requires that
the user has already added at least one layer before. If lowerdir is
specified again without a leading ":" then all previous layers are
dropped and replaced with the new layers. If lowerdir is specified and
empty than all layers are simply dropped.

An additional change is that overlayfs will now parse and resolve layers
right when they are specified in fsconfig() instead of deferring until
super block creation. This allows users to receive early errors.

It also allows users to actually use up to 500 layers something which
was theoretically possible but ended up not working due to the mount
option string passed via mount(2) being too large.

This also allows a more privileged process to set config options for a
lesser privileged process as the creds for fsconfig() and the creds for
fsopen() can differ. We could restrict that they match by enforcing that
the creds of fsopen() and fsconfig() match but I don't see why that
needs to be the case and allows for a good delegation mechanism.

Plus, in the future it means we're able to extend overlayfs mount
options and allow users to specify layers via file descriptors instead
of paths:

        fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower1", dirfd);

        /* append */
        fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower2", dirfd);

        /* append */
        fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower3", dirfd);

        /* clear all layers specified until now */
        fsconfig(FSCONFIG_SET_STRING, "lowerdir", NULL, 0);

This would be especially nice if users create an overlayfs mount on top
of idmapped layers or just in general private mounts created via
open_tree(OPEN_TREE_CLONE). Those mounts would then never have to appear
anywhere in the filesystem. But for now just do the minimal thing.

We should probably aim to move more validation into ovl_fs_parse_param()
so users get errors before fsconfig(FSCONFIG_CMD_CREATE). But that can
be done in additional patches later.

Link: https://github.com/util-linux/util-linux/issues/2287
Link: https://github.com/util-linux/util-linux/issues/1992
Link: https://bugs.archlinux.org/task/78702
Link: https://lore.kernel.org/linux-unionfs/20230530-klagen-zudem-32c0908c2108@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/overlayfs/Makefile       |   2 +-
 fs/overlayfs/layer_params.c | 288 ++++++++++++++++++++++++++++++++++++++
 fs/overlayfs/ovl_entry.h    |  30 ++++
 fs/overlayfs/super.c        | 328 +++++++++++++++-----------------------------
 4 files changed, 431 insertions(+), 217 deletions(-)

diff --git a/fs/overlayfs/Makefile b/fs/overlayfs/Makefile
index 9164c585eb2f..a3ad81c2e64e 100644
--- a/fs/overlayfs/Makefile
+++ b/fs/overlayfs/Makefile
@@ -6,4 +6,4 @@
 obj-$(CONFIG_OVERLAY_FS) += overlay.o
 
 overlay-objs := super.o namei.o util.o inode.o file.o dir.o readdir.o \
-		copy_up.o export.o
+		copy_up.o export.o layer_params.o
diff --git a/fs/overlayfs/layer_params.c b/fs/overlayfs/layer_params.c
new file mode 100644
index 000000000000..29907afc9d0d
--- /dev/null
+++ b/fs/overlayfs/layer_params.c
@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/posix_acl_xattr.h>
+#include <linux/xattr.h>
+#include "overlayfs.h"
+
+static size_t ovl_parse_param_split_lowerdirs(char *str)
+{
+	size_t ctr = 1;
+	char *s, *d;
+
+	for (s = d = str;; s++, d++) {
+		if (*s == '\\') {
+			s++;
+		} else if (*s == ':') {
+			*d = '\0';
+			ctr++;
+			continue;
+		}
+		*d = *s;
+		if (!*s)
+			break;
+	}
+	return ctr;
+}
+
+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;
+}
+
+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;
+}
+
+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;
+}
+
+/*
+ * Parse lowerdir= mount option:
+ *
+ * (1) lowerdir=/lower1:/lower2:/lower3
+ *     Set "/lower1", "/lower2", and "/lower3" as 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.
+ */
+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;
+	size_t nr_lower = 0, nr = 0;
+	bool append = false;
+
+	/* Enforce that users are forced to specify a single ':'. */
+	if (strncmp(name, "::", 2) == 0)
+		return -EINVAL;
+
+	/*
+	 * 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 (*name == ':') {
+		/*
+		 * 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)
+			return -EINVAL;
+
+		/*
+		 * Drop the leading. We'll create the final mount option
+		 * string for the lower layers when we create the superblock.
+		 */
+		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 > 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;
+	}
+
+	/* By (1) and (2) we know nr <= nr_lower <= capacity. */
+	dup_iter = dup;
+	for (nr = ctx->nr; nr < nr_lower; nr++) {
+		l = &ctx->lower[nr];
+
+		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;
+
+		dup_iter = strchr(dup_iter, '\0') + 1;
+	}
+	ctx->nr = nr_lower;
+	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;
+}
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index fd11fe6d6d45..269a9a6f177b 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -85,6 +85,36 @@ struct ovl_fs {
 	errseq_t errseq;
 };
 
+#define OVL_MAX_STACK 500
+
+struct ovl_fs_context_layer {
+	char *name;
+	struct path path;
+};
+
+/*
+ * These options imply different behavior when they are explicitly
+ * specified than when they are left in their default state.
+ */
+#define OVL_METACOPY_SET	BIT(0)
+#define OVL_REDIRECT_SET	BIT(1)
+#define OVL_NFS_EXPORT_SET	BIT(2)
+#define OVL_INDEX_SET		BIT(3)
+
+struct ovl_fs_context {
+	struct path upper;
+	struct path work;
+	size_t capacity;
+	size_t nr;
+	u8 set;
+	struct ovl_fs_context_layer *lower;
+};
+
+int ovl_parse_param_upperdir(const char *name, struct fs_context *fc,
+			     bool workdir);
+int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc);
+void ovl_parse_param_drop_lowerdir(struct ovl_fs_context *ctx);
+
 static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)
 {
 	return ofs->layers[0].mnt;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ceaf05743f45..35c61a1d0886 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -27,8 +27,6 @@ MODULE_LICENSE("GPL");
 
 struct ovl_dir_cache;
 
-#define OVL_MAX_STACK 500
-
 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,
@@ -97,8 +95,11 @@ static const struct constant_table ovl_parameter_xino[] = {
 	{}
 };
 
+#define fsparam_string_empty(NAME, OPT) \
+	__fsparam(fs_param_is_string, NAME, OPT, fs_param_can_be_empty, NULL)
+
 static const struct fs_parameter_spec ovl_parameter_spec[] = {
-	fsparam_string("lowerdir",          Opt_lowerdir),
+	fsparam_string_empty("lowerdir",    Opt_lowerdir),
 	fsparam_string("upperdir",          Opt_upperdir),
 	fsparam_string("workdir",           Opt_workdir),
 	fsparam_flag("default_permissions", Opt_default_permissions),
@@ -113,15 +114,6 @@ static const struct fs_parameter_spec ovl_parameter_spec[] = {
 	{}
 };
 
-#define OVL_METACOPY_SET	BIT(0)
-#define OVL_REDIRECT_SET	BIT(1)
-#define OVL_NFS_EXPORT_SET	BIT(2)
-#define OVL_INDEX_SET		BIT(3)
-
-struct ovl_fs_context {
-	u8 set;
-};
-
 static void ovl_dentry_release(struct dentry *dentry)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;
@@ -706,69 +698,6 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
 	goto out_unlock;
 }
 
-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_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 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_check_namelen(const struct path *path, struct ovl_fs *ofs,
 			     const char *name)
 {
@@ -789,10 +718,6 @@ static int ovl_lower_dir(const char *name, struct path *path,
 	int fh_type;
 	int err;
 
-	err = ovl_mount_dir_noesc(name, path);
-	if (err)
-		return err;
-
 	err = ovl_check_namelen(path, ofs, name);
 	if (err)
 		return err;
@@ -841,26 +766,6 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 	return ok;
 }
 
-static unsigned int ovl_split_lowerdirs(char *str)
-{
-	unsigned int ctr = 1;
-	char *s, *d;
-
-	for (s = d = str;; s++, d++) {
-		if (*s == '\\') {
-			s++;
-		} else if (*s == ':') {
-			*d = '\0';
-			ctr++;
-			continue;
-		}
-		*d = *s;
-		if (!*s)
-			break;
-	}
-	return ctr;
-}
-
 static int ovl_own_xattr_get(const struct xattr_handler *handler,
 			     struct dentry *dentry, struct inode *inode,
 			     const char *name, void *buffer, size_t size)
@@ -961,15 +866,12 @@ static int ovl_report_in_use(struct ovl_fs *ofs, const char *name)
 }
 
 static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
-			 struct ovl_layer *upper_layer, struct path *upperpath)
+			 struct ovl_layer *upper_layer,
+			 const struct path *upperpath)
 {
 	struct vfsmount *upper_mnt;
 	int err;
 
-	err = ovl_mount_dir(ofs->config.upperdir, upperpath);
-	if (err)
-		goto out;
-
 	/* Upperdir path should not be r/o */
 	if (__mnt_is_readonly(upperpath->mnt)) {
 		pr_err("upper fs is r/o, try multi-lower layers mount\n");
@@ -1256,46 +1158,37 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 }
 
 static int ovl_get_workdir(struct super_block *sb, struct ovl_fs *ofs,
-			   const struct path *upperpath)
+			   const struct path *upperpath,
+			   const struct path *workpath)
 {
 	int err;
-	struct path workpath = { };
-
-	err = ovl_mount_dir(ofs->config.workdir, &workpath);
-	if (err)
-		goto out;
 
 	err = -EINVAL;
-	if (upperpath->mnt != workpath.mnt) {
+	if (upperpath->mnt != workpath->mnt) {
 		pr_err("workdir and upperdir must reside under the same mount\n");
-		goto out;
+		return err;
 	}
-	if (!ovl_workdir_ok(workpath.dentry, upperpath->dentry)) {
+	if (!ovl_workdir_ok(workpath->dentry, upperpath->dentry)) {
 		pr_err("workdir and upperdir must be separate subtrees\n");
-		goto out;
+		return err;
 	}
 
-	ofs->workbasedir = dget(workpath.dentry);
+	ofs->workbasedir = dget(workpath->dentry);
 
 	if (ovl_inuse_trylock(ofs->workbasedir)) {
 		ofs->workdir_locked = true;
 	} else {
 		err = ovl_report_in_use(ofs, "workdir");
 		if (err)
-			goto out;
+			return err;
 	}
 
 	err = ovl_setup_trap(sb, ofs->workbasedir, &ofs->workbasedir_trap,
 			     "workdir");
 	if (err)
-		goto out;
-
-	err = ovl_make_workdir(sb, ofs, &workpath);
-
-out:
-	path_put(&workpath);
+		return err;
 
-	return err;
+	return ovl_make_workdir(sb, ofs, workpath);
 }
 
 static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs,
@@ -1449,14 +1342,13 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
 }
 
 static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
-			  struct path *stack, unsigned int numlower,
-			  struct ovl_layer *layers)
+			  struct ovl_fs_context *ctx, struct ovl_layer *layers)
 {
 	int err;
 	unsigned int i;
 
 	err = -ENOMEM;
-	ofs->fs = kcalloc(numlower + 1, sizeof(struct ovl_sb), GFP_KERNEL);
+	ofs->fs = kcalloc(ctx->nr + 1, sizeof(struct ovl_sb), GFP_KERNEL);
 	if (ofs->fs == NULL)
 		goto out;
 
@@ -1480,12 +1372,13 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 		ofs->fs[0].is_lower = false;
 	}
 
-	for (i = 0; i < numlower; i++) {
+	for (i = 0; i < ctx->nr; i++) {
+		struct ovl_fs_context_layer *l = &ctx->lower[i];
 		struct vfsmount *mnt;
 		struct inode *trap;
 		int fsid;
 
-		err = fsid = ovl_get_fsid(ofs, &stack[i]);
+		err = fsid = ovl_get_fsid(ofs, &l->path);
 		if (err < 0)
 			goto out;
 
@@ -1496,11 +1389,11 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 		 * the upperdir/workdir is in fact in-use by our
 		 * upperdir/workdir.
 		 */
-		err = ovl_setup_trap(sb, stack[i].dentry, &trap, "lowerdir");
+		err = ovl_setup_trap(sb, l->path.dentry, &trap, "lowerdir");
 		if (err)
 			goto out;
 
-		if (ovl_is_inuse(stack[i].dentry)) {
+		if (ovl_is_inuse(l->path.dentry)) {
 			err = ovl_report_in_use(ofs, "lowerdir");
 			if (err) {
 				iput(trap);
@@ -1508,7 +1401,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 			}
 		}
 
-		mnt = clone_private_mount(&stack[i]);
+		mnt = clone_private_mount(&l->path);
 		err = PTR_ERR(mnt);
 		if (IS_ERR(mnt)) {
 			pr_err("failed to clone lowerpath\n");
@@ -1569,63 +1462,86 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 }
 
 static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
-				const char *lower, unsigned int numlower,
-				struct ovl_fs *ofs, struct ovl_layer *layers)
+					    struct ovl_fs_context *ctx,
+					    struct ovl_fs *ofs,
+					    struct ovl_layer *layers)
 {
 	int err;
-	struct path *stack = NULL;
 	unsigned int i;
 	struct ovl_entry *oe;
+	size_t len;
+	char *lowerdir;
+	struct ovl_fs_context_layer *l;
 
-	if (!ofs->config.upperdir && numlower == 1) {
+	if (!ofs->config.upperdir && ctx->nr == 1) {
 		pr_err("at least 2 lowerdir are needed while upperdir nonexistent\n");
 		return ERR_PTR(-EINVAL);
 	}
 
-	stack = kcalloc(numlower, sizeof(struct path), GFP_KERNEL);
-	if (!stack)
-		return ERR_PTR(-ENOMEM);
-
 	err = -EINVAL;
-	for (i = 0; i < numlower; i++) {
-		err = ovl_lower_dir(lower, &stack[i], ofs, &sb->s_stack_depth);
+	len = 0;
+	for (i = 0; i < ctx->nr; i++) {
+		l = &ctx->lower[i];
+
+		err = ovl_lower_dir(l->name, &l->path, ofs, &sb->s_stack_depth);
 		if (err)
-			goto out_err;
+			return ERR_PTR(err);
 
-		lower = strchr(lower, '\0') + 1;
+		len += strlen(l->name);
 	}
 
 	err = -EINVAL;
 	sb->s_stack_depth++;
 	if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
 		pr_err("maximum fs stacking depth exceeded\n");
-		goto out_err;
+		return ERR_PTR(err);
+	}
+
+	/*
+	 * Create a string of all lower layers that we store in
+	 * ofs->config.lowerdir which we can display to userspace in
+	 * mount options. For example, this assembles "/lower1",
+	 * "/lower2" into "/lower1:/lower2".
+	 *
+	 * We need to make sure we add a ':'. Thus, we need to account
+	 * for the separators when allocating space when multiple layers
+	 * are specified. That should be easy since we know that ctx->nr
+	 * >= 1. So we know that ctx->nr - 1 will be correct for the
+	 * base case ctx->nr == 1 and all other cases.
+	 */
+	len += ctx->nr - 1;
+	len++; /* and leave room for \0 */
+	lowerdir = kzalloc(len, GFP_KERNEL_ACCOUNT);
+	if (!lowerdir)
+		return ERR_PTR(-ENOMEM);
+
+	ofs->config.lowerdir = lowerdir;
+	for (i = 0; i < ctx->nr; i++) {
+		l = &ctx->lower[i];
+
+		len = strlen(l->name);
+		memcpy(lowerdir, l->name, len);
+		if ((ctx->nr > 1) && ((i + 1) != ctx->nr))
+			lowerdir[len++] = ':';
+		lowerdir += len;
 	}
 
-	err = ovl_get_layers(sb, ofs, stack, numlower, layers);
+	err = ovl_get_layers(sb, ofs, ctx, layers);
 	if (err)
-		goto out_err;
+		return ERR_PTR(err);
 
 	err = -ENOMEM;
-	oe = ovl_alloc_entry(numlower);
+	oe = ovl_alloc_entry(ctx->nr);
 	if (!oe)
-		goto out_err;
+		return ERR_PTR(err);
 
-	for (i = 0; i < numlower; i++) {
-		oe->lowerstack[i].dentry = dget(stack[i].dentry);
-		oe->lowerstack[i].layer = &ofs->layers[i+1];
+	for (i = 0; i < ctx->nr; i++) {
+		l = &ctx->lower[i];
+		oe->lowerstack[i].dentry = dget(l->path.dentry);
+		oe->lowerstack[i].layer = &ofs->layers[i + 1];
 	}
 
-out:
-	for (i = 0; i < numlower; i++)
-		path_put(&stack[i]);
-	kfree(stack);
-
 	return oe;
-
-out_err:
-	oe = ERR_PTR(err);
-	goto out;
 }
 
 /*
@@ -1735,6 +1651,12 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 	ovl_set_upperdata(d_inode(root));
 	ovl_inode_init(d_inode(root), &oip, ino, fsid);
 	ovl_dentry_update_reval(root, upperdentry, DCACHE_OP_WEAK_REVALIDATE);
+	/*
+	 * We're going to put upper path when we call
+	 * fs_context_operations->free() take an additional
+	 * reference so we can just call path_put().
+	 */
+	dget(upperdentry);
 
 	return root;
 }
@@ -1746,8 +1668,6 @@ static int ovl_parse_param(struct fs_context *fc, struct fs_parameter *param)
 	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;
 	int opt;
 	char *sval;
 
@@ -1765,37 +1685,13 @@ static int ovl_parse_param(struct fs_context *fc, struct fs_parameter *param)
 
 	switch (opt) {
 	case Opt_lowerdir:
-		dup = kstrdup(param->string, GFP_KERNEL);
-		if (!dup) {
-			path_put(&path);
-			err = -ENOMEM;
-			break;
-		}
-
-		kfree(config->lowerdir);
-		config->lowerdir = dup;
+		err = ovl_parse_param_lowerdir(param->string, fc);
 		break;
 	case Opt_upperdir:
-		dup = kstrdup(param->string, GFP_KERNEL);
-		if (!dup) {
-			path_put(&path);
-			err = -ENOMEM;
-			break;
-		}
-
-		kfree(config->upperdir);
-		config->upperdir = dup;
-		break;
+		fallthrough;
 	case Opt_workdir:
-		dup = kstrdup(param->string, GFP_KERNEL);
-		if (!dup) {
-			path_put(&path);
-			err = -ENOMEM;
-			break;
-		}
-
-		kfree(config->workdir);
-		config->workdir = dup;
+		err = ovl_parse_param_upperdir(param->string, fc,
+					       (Opt_workdir == opt));
 		break;
 	case Opt_default_permissions:
 		config->default_permissions = true;
@@ -1873,13 +1769,11 @@ static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
 	struct ovl_fs_context *ctx = fc->fs_private;
-	struct path upperpath = {};
+
 	struct dentry *root_dentry;
 	struct ovl_entry *oe;
 	struct ovl_layer *layers;
 	struct cred *cred;
-	char *splitlower = NULL;
-	unsigned int numlower;
 	int err;
 
 	err = -EIO;
@@ -1898,28 +1792,20 @@ static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (err)
 		goto out_err;
 
+	/*
+	 * Check ctx->nr instead of ofs->config.lowerdir since we're
+	 * going to set ofs->config.lowerdir here after we know that the
+	 * user specified all layers.
+	 */
 	err = -EINVAL;
-	if (!ofs->config.lowerdir) {
+	if (ctx->nr == 0) {
 		if (fc->sb_flags & SB_SILENT)
 			pr_err("missing 'lowerdir'\n");
 		goto out_err;
 	}
 
 	err = -ENOMEM;
-	splitlower = kstrdup(ofs->config.lowerdir, GFP_KERNEL);
-	if (!splitlower)
-		goto out_err;
-
-	err = -EINVAL;
-	numlower = ovl_split_lowerdirs(splitlower);
-	if (numlower > OVL_MAX_STACK) {
-		pr_err("too many lower directories, limit is %d\n",
-		       OVL_MAX_STACK);
-		goto out_err;
-	}
-
-	err = -ENOMEM;
-	layers = kcalloc(numlower + 1, sizeof(struct ovl_layer), GFP_KERNEL);
+	layers = kcalloc(ctx->nr + 1, sizeof(struct ovl_layer), GFP_KERNEL);
 	if (!layers)
 		goto out_err;
 
@@ -1951,7 +1837,7 @@ static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 			goto out_err;
 		}
 
-		err = ovl_get_upper(sb, ofs, &layers[0], &upperpath);
+		err = ovl_get_upper(sb, ofs, &layers[0], &ctx->upper);
 		if (err)
 			goto out_err;
 
@@ -1965,7 +1851,7 @@ static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 			}
 		}
 
-		err = ovl_get_workdir(sb, ofs, &upperpath);
+		err = ovl_get_workdir(sb, ofs, &ctx->upper, &ctx->work);
 		if (err)
 			goto out_err;
 
@@ -1975,7 +1861,7 @@ static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 		sb->s_stack_depth = upper_sb->s_stack_depth;
 		sb->s_time_gran = upper_sb->s_time_gran;
 	}
-	oe = ovl_get_lowerstack(sb, splitlower, numlower, ofs, layers);
+	oe = ovl_get_lowerstack(sb, ctx, ofs, layers);
 	err = PTR_ERR(oe);
 	if (IS_ERR(oe))
 		goto out_err;
@@ -1990,7 +1876,7 @@ static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 	}
 
 	if (!ovl_force_readonly(ofs) && ofs->config.index) {
-		err = ovl_get_indexdir(sb, ofs, oe, &upperpath);
+		err = ovl_get_indexdir(sb, ofs, oe, &ctx->upper);
 		if (err)
 			goto out_free_oe;
 
@@ -2031,13 +1917,10 @@ static int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_iflags |= SB_I_SKIP_SYNC;
 
 	err = -ENOMEM;
-	root_dentry = ovl_get_root(sb, upperpath.dentry, oe);
+	root_dentry = ovl_get_root(sb, ctx->upper.dentry, oe);
 	if (!root_dentry)
 		goto out_free_oe;
 
-	mntput(upperpath.mnt);
-	kfree(splitlower);
-
 	sb->s_root = root_dentry;
 
 	return 0;
@@ -2056,6 +1939,10 @@ static int ovl_get_tree(struct fs_context *fc)
 
 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);
 }
 
@@ -2100,6 +1987,15 @@ static int ovl_init_fs_context(struct fs_context *fc)
 	if (!ctx)
 		goto out_err;
 
+	/*
+	 * 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;

-- 
2.34.1

Re: [PATCH v2 2/2] ovl: modify layer parameter parsing

[Amir Goldstein]

On Fri, Jun 9, 2023 at 6:42 PM Christian Brauner <brauner@kernel.org> wrote:
>
> We ran into issues where mount(8) passed multiple lower layers as one
> big string through fsconfig(). But the fsconfig() FSCONFIG_SET_STRING
> option is limited to 256 bytes in strndup_user(). While this would be
> fixable by extending the fsconfig() buffer I'd rather encourage users to
> append layers via multiple fsconfig() calls as the interface allows
> nicely for this. This has also been requested as a feature before.
>
> With this port to the new mount api the following will be possible:
>
>         fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", "/lower1", 0);
>
>         /* set upper layer */
>         fsconfig(fs_fd, FSCONFIG_SET_STRING, "upperdir", "/upper", 0);
>
>         /* append "/lower2", "/lower3", and "/lower4" */
>         fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", ":/lower2:/lower3:/lower4", 0);
>
>         /* turn index feature on */
>         fsconfig(fs_fd, FSCONFIG_SET_STRING, "index", "on", 0);
>
>         /* append "/lower5" */
>         fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", ":/lower5", 0);
>
> Specifying ':' would have been rejected so this isn't a regression. And
> we can't simply use "lowerdir=/lower" to append on top of existing
> layers as "lowerdir=/lower,lowerdir=/other-lower" would make
> "/other-lower" the only lower layer so we'd break uapi if we changed
> this. So the ':' prefix seems a good compromise.
>
> Users can choose to specify multiple layers at once or individual
> layers. A layer is appended if it starts with ":". This requires that
> the user has already added at least one layer before. If lowerdir is
> specified again without a leading ":" then all previous layers are
> dropped and replaced with the new layers. If lowerdir is specified and
> empty than all layers are simply dropped.
>
> An additional change is that overlayfs will now parse and resolve layers
> right when they are specified in fsconfig() instead of deferring until
> super block creation. This allows users to receive early errors.
>
> It also allows users to actually use up to 500 layers something which
> was theoretically possible but ended up not working due to the mount
> option string passed via mount(2) being too large.
>
> This also allows a more privileged process to set config options for a
> lesser privileged process as the creds for fsconfig() and the creds for
> fsopen() can differ. We could restrict that they match by enforcing that
> the creds of fsopen() and fsconfig() match but I don't see why that
> needs to be the case and allows for a good delegation mechanism.
>
> Plus, in the future it means we're able to extend overlayfs mount
> options and allow users to specify layers via file descriptors instead
> of paths:
>
>         fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower1", dirfd);
>
>         /* append */
>         fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower2", dirfd);
>
>         /* append */
>         fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower3", dirfd);
>
>         /* clear all layers specified until now */
>         fsconfig(FSCONFIG_SET_STRING, "lowerdir", NULL, 0);
>
> This would be especially nice if users create an overlayfs mount on top
> of idmapped layers or just in general private mounts created via
> open_tree(OPEN_TREE_CLONE). Those mounts would then never have to appear
> anywhere in the filesystem. But for now just do the minimal thing.
>
> We should probably aim to move more validation into ovl_fs_parse_param()
> so users get errors before fsconfig(FSCONFIG_CMD_CREATE). But that can
> be done in additional patches later.
>
> Link: https://github.com/util-linux/util-linux/issues/2287
> Link: https://github.com/util-linux/util-linux/issues/1992
> Link: https://bugs.archlinux.org/task/78702
> Link: https://lore.kernel.org/linux-unionfs/20230530-klagen-zudem-32c0908c2108@brauner
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> ---
>  fs/overlayfs/Makefile       |   2 +-
>  fs/overlayfs/layer_params.c | 288 ++++++++++++++++++++++++++++++++++++++
>  fs/overlayfs/ovl_entry.h    |  30 ++++
>  fs/overlayfs/super.c        | 328 +++++++++++++++-----------------------------
>  4 files changed, 431 insertions(+), 217 deletions(-)
>
> diff --git a/fs/overlayfs/Makefile b/fs/overlayfs/Makefile
> index 9164c585eb2f..a3ad81c2e64e 100644
> --- a/fs/overlayfs/Makefile
> +++ b/fs/overlayfs/Makefile
> @@ -6,4 +6,4 @@
>  obj-$(CONFIG_OVERLAY_FS) += overlay.o
>
>  overlay-objs := super.o namei.o util.o inode.o file.o dir.o readdir.o \
> -               copy_up.o export.o
> +               copy_up.o export.o layer_params.o
> diff --git a/fs/overlayfs/layer_params.c b/fs/overlayfs/layer_params.c
> new file mode 100644
> index 000000000000..29907afc9d0d
> --- /dev/null
> +++ b/fs/overlayfs/layer_params.c

params.c please
and please move all the params parsing code here
not only the layers parsing.

> @@ -0,0 +1,288 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/fs.h>
> +#include <linux/namei.h>
> +#include <linux/fs_context.h>
> +#include <linux/fs_parser.h>
> +#include <linux/posix_acl_xattr.h>
> +#include <linux/xattr.h>
> +#include "overlayfs.h"
> +
> +static size_t ovl_parse_param_split_lowerdirs(char *str)
> +{
> +       size_t ctr = 1;
> +       char *s, *d;
> +
> +       for (s = d = str;; s++, d++) {
> +               if (*s == '\\') {
> +                       s++;
> +               } else if (*s == ':') {
> +                       *d = '\0';
> +                       ctr++;
> +                       continue;
> +               }
> +               *d = *s;
> +               if (!*s)
> +                       break;
> +       }
> +       return ctr;
> +}
> +
> +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;
> +}
> +
> +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;
> +}
> +
> +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;
> +}
> +
> +/*
> + * Parse lowerdir= mount option:
> + *
> + * (1) lowerdir=/lower1:/lower2:/lower3
> + *     Set "/lower1", "/lower2", and "/lower3" as 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.
> + */
> +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;
> +       size_t nr_lower = 0, nr = 0;
> +       bool append = false;
> +
> +       /* Enforce that users are forced to specify a single ':'. */
> +       if (strncmp(name, "::", 2) == 0)
> +               return -EINVAL;
> +
> +       /*
> +        * 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 (*name == ':') {
> +               /*
> +                * 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)
> +                       return -EINVAL;
> +
> +               /*
> +                * Drop the leading. We'll create the final mount option
> +                * string for the lower layers when we create the superblock.
> +                */
> +               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 > 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;
> +       }
> +
> +       /* By (1) and (2) we know nr <= nr_lower <= capacity. */
> +       dup_iter = dup;
> +       for (nr = ctx->nr; nr < nr_lower; nr++) {
> +               l = &ctx->lower[nr];
> +
> +               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;
> +
> +               dup_iter = strchr(dup_iter, '\0') + 1;
> +       }
> +       ctx->nr = nr_lower;
> +       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;
> +}
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index fd11fe6d6d45..269a9a6f177b 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -85,6 +85,36 @@ struct ovl_fs {
>         errseq_t errseq;
>  };
>
> +#define OVL_MAX_STACK 500
> +
> +struct ovl_fs_context_layer {
> +       char *name;
> +       struct path path;
> +};
> +
> +/*
> + * These options imply different behavior when they are explicitly
> + * specified than when they are left in their default state.
> + */
> +#define OVL_METACOPY_SET       BIT(0)
> +#define OVL_REDIRECT_SET       BIT(1)
> +#define OVL_NFS_EXPORT_SET     BIT(2)
> +#define OVL_INDEX_SET          BIT(3)
> +
> +struct ovl_fs_context {
> +       struct path upper;
> +       struct path work;
> +       size_t capacity;
> +       size_t nr;
> +       u8 set;
> +       struct ovl_fs_context_layer *lower;
> +};
> +
> +int ovl_parse_param_upperdir(const char *name, struct fs_context *fc,
> +                            bool workdir);
> +int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc);
> +void ovl_parse_param_drop_lowerdir(struct ovl_fs_context *ctx);
> +

Please move all this to overlayfs.h.
I don't think there is a good reason for it to be in this file.


>  static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)
>  {
>         return ofs->layers[0].mnt;
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index ceaf05743f45..35c61a1d0886 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -27,8 +27,6 @@ MODULE_LICENSE("GPL");
>
>  struct ovl_dir_cache;
>
> -#define OVL_MAX_STACK 500
> -
>  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,
> @@ -97,8 +95,11 @@ static const struct constant_table ovl_parameter_xino[] = {
>         {}
>  };
>
> +#define fsparam_string_empty(NAME, OPT) \
> +       __fsparam(fs_param_is_string, NAME, OPT, fs_param_can_be_empty, NULL)
> +
>  static const struct fs_parameter_spec ovl_parameter_spec[] = {
> -       fsparam_string("lowerdir",          Opt_lowerdir),
> +       fsparam_string_empty("lowerdir",    Opt_lowerdir),
>         fsparam_string("upperdir",          Opt_upperdir),
>         fsparam_string("workdir",           Opt_workdir),
>         fsparam_flag("default_permissions", Opt_default_permissions),
> @@ -113,15 +114,6 @@ static const struct fs_parameter_spec ovl_parameter_spec[] = {
>         {}
>  };
>
> -#define OVL_METACOPY_SET       BIT(0)
> -#define OVL_REDIRECT_SET       BIT(1)
> -#define OVL_NFS_EXPORT_SET     BIT(2)
> -#define OVL_INDEX_SET          BIT(3)
> -
> -struct ovl_fs_context {
> -       u8 set;
> -};
> -
>  static void ovl_dentry_release(struct dentry *dentry)
>  {
>         struct ovl_entry *oe = dentry->d_fsdata;
> @@ -706,69 +698,6 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
>         goto out_unlock;
>  }
>
> -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_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 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_check_namelen(const struct path *path, struct ovl_fs *ofs,
>                              const char *name)
>  {
> @@ -789,10 +718,6 @@ static int ovl_lower_dir(const char *name, struct path *path,
>         int fh_type;
>         int err;
>
> -       err = ovl_mount_dir_noesc(name, path);
> -       if (err)
> -               return err;
> -
>         err = ovl_check_namelen(path, ofs, name);
>         if (err)
>                 return err;
> @@ -841,26 +766,6 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
>         return ok;
>  }
>
> -static unsigned int ovl_split_lowerdirs(char *str)
> -{
> -       unsigned int ctr = 1;
> -       char *s, *d;
> -
> -       for (s = d = str;; s++, d++) {
> -               if (*s == '\\') {
> -                       s++;
> -               } else if (*s == ':') {
> -                       *d = '\0';
> -                       ctr++;
> -                       continue;
> -               }
> -               *d = *s;
> -               if (!*s)
> -                       break;
> -       }
> -       return ctr;
> -}
> -
>  static int ovl_own_xattr_get(const struct xattr_handler *handler,
>                              struct dentry *dentry, struct inode *inode,
>                              const char *name, void *buffer, size_t size)
> @@ -961,15 +866,12 @@ static int ovl_report_in_use(struct ovl_fs *ofs, const char *name)
>  }
>
>  static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
> -                        struct ovl_layer *upper_layer, struct path *upperpath)
> +                        struct ovl_layer *upper_layer,
> +                        const struct path *upperpath)
>  {
>         struct vfsmount *upper_mnt;
>         int err;
>
> -       err = ovl_mount_dir(ofs->config.upperdir, upperpath);
> -       if (err)
> -               goto out;
> -
>         /* Upperdir path should not be r/o */
>         if (__mnt_is_readonly(upperpath->mnt)) {
>                 pr_err("upper fs is r/o, try multi-lower layers mount\n");
> @@ -1256,46 +1158,37 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
>  }
>
>  static int ovl_get_workdir(struct super_block *sb, struct ovl_fs *ofs,
> -                          const struct path *upperpath)
> +                          const struct path *upperpath,
> +                          const struct path *workpath)
>  {
>         int err;
> -       struct path workpath = { };
> -
> -       err = ovl_mount_dir(ofs->config.workdir, &workpath);
> -       if (err)
> -               goto out;
>
>         err = -EINVAL;
> -       if (upperpath->mnt != workpath.mnt) {
> +       if (upperpath->mnt != workpath->mnt) {
>                 pr_err("workdir and upperdir must reside under the same mount\n");
> -               goto out;
> +               return err;
>         }
> -       if (!ovl_workdir_ok(workpath.dentry, upperpath->dentry)) {
> +       if (!ovl_workdir_ok(workpath->dentry, upperpath->dentry)) {
>                 pr_err("workdir and upperdir must be separate subtrees\n");
> -               goto out;
> +               return err;
>         }
>
> -       ofs->workbasedir = dget(workpath.dentry);
> +       ofs->workbasedir = dget(workpath->dentry);
>
>         if (ovl_inuse_trylock(ofs->workbasedir)) {
>                 ofs->workdir_locked = true;
>         } else {
>                 err = ovl_report_in_use(ofs, "workdir");
>                 if (err)
> -                       goto out;
> +                       return err;
>         }
>
>         err = ovl_setup_trap(sb, ofs->workbasedir, &ofs->workbasedir_trap,
>                              "workdir");
>         if (err)
> -               goto out;
> -
> -       err = ovl_make_workdir(sb, ofs, &workpath);
> -
> -out:
> -       path_put(&workpath);
> +               return err;
>
> -       return err;
> +       return ovl_make_workdir(sb, ofs, workpath);
>  }
>
>  static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs,
> @@ -1449,14 +1342,13 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
>  }
>
>  static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> -                         struct path *stack, unsigned int numlower,
> -                         struct ovl_layer *layers)
> +                         struct ovl_fs_context *ctx, struct ovl_layer *layers)
>  {
>         int err;
>         unsigned int i;
>
>         err = -ENOMEM;
> -       ofs->fs = kcalloc(numlower + 1, sizeof(struct ovl_sb), GFP_KERNEL);
> +       ofs->fs = kcalloc(ctx->nr + 1, sizeof(struct ovl_sb), GFP_KERNEL);
>         if (ofs->fs == NULL)
>                 goto out;
>
> @@ -1480,12 +1372,13 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>                 ofs->fs[0].is_lower = false;
>         }
>
> -       for (i = 0; i < numlower; i++) {
> +       for (i = 0; i < ctx->nr; i++) {
> +               struct ovl_fs_context_layer *l = &ctx->lower[i];
>                 struct vfsmount *mnt;
>                 struct inode *trap;
>                 int fsid;
>
> -               err = fsid = ovl_get_fsid(ofs, &stack[i]);
> +               err = fsid = ovl_get_fsid(ofs, &l->path);
>                 if (err < 0)
>                         goto out;
>
> @@ -1496,11 +1389,11 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>                  * the upperdir/workdir is in fact in-use by our
>                  * upperdir/workdir.
>                  */
> -               err = ovl_setup_trap(sb, stack[i].dentry, &trap, "lowerdir");
> +               err = ovl_setup_trap(sb, l->path.dentry, &trap, "lowerdir");
>                 if (err)
>                         goto out;
>
> -               if (ovl_is_inuse(stack[i].dentry)) {
> +               if (ovl_is_inuse(l->path.dentry)) {
>                         err = ovl_report_in_use(ofs, "lowerdir");
>                         if (err) {
>                                 iput(trap);
> @@ -1508,7 +1401,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>                         }
>                 }
>
> -               mnt = clone_private_mount(&stack[i]);
> +               mnt = clone_private_mount(&l->path);
>                 err = PTR_ERR(mnt);
>                 if (IS_ERR(mnt)) {
>                         pr_err("failed to clone lowerpath\n");
> @@ -1569,63 +1462,86 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>  }
>
>  static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> -                               const char *lower, unsigned int numlower,
> -                               struct ovl_fs *ofs, struct ovl_layer *layers)
> +                                           struct ovl_fs_context *ctx,
> +                                           struct ovl_fs *ofs,
> +                                           struct ovl_layer *layers)
>  {
>         int err;
> -       struct path *stack = NULL;
>         unsigned int i;
>         struct ovl_entry *oe;
> +       size_t len;
> +       char *lowerdir;
> +       struct ovl_fs_context_layer *l;
>
> -       if (!ofs->config.upperdir && numlower == 1) {
> +       if (!ofs->config.upperdir && ctx->nr == 1) {
>                 pr_err("at least 2 lowerdir are needed while upperdir nonexistent\n");
>                 return ERR_PTR(-EINVAL);
>         }
>
> -       stack = kcalloc(numlower, sizeof(struct path), GFP_KERNEL);
> -       if (!stack)
> -               return ERR_PTR(-ENOMEM);
> -
>         err = -EINVAL;
> -       for (i = 0; i < numlower; i++) {
> -               err = ovl_lower_dir(lower, &stack[i], ofs, &sb->s_stack_depth);
> +       len = 0;
> +       for (i = 0; i < ctx->nr; i++) {
> +               l = &ctx->lower[i];
> +
> +               err = ovl_lower_dir(l->name, &l->path, ofs, &sb->s_stack_depth);
>                 if (err)
> -                       goto out_err;
> +                       return ERR_PTR(err);
>
> -               lower = strchr(lower, '\0') + 1;
> +               len += strlen(l->name);
>         }
>
>         err = -EINVAL;
>         sb->s_stack_depth++;
>         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
>                 pr_err("maximum fs stacking depth exceeded\n");
> -               goto out_err;
> +               return ERR_PTR(err);
> +       }
.> +
> +       /*
> +        * Create a string of all lower layers that we store in
> +        * ofs->config.lowerdir which we can display to userspace in
> +        * mount options. For example, this assembles "/lower1",
> +        * "/lower2" into "/lower1:/lower2".
> +        *
> +        * We need to make sure we add a ':'. Thus, we need to account
> +        * for the separators when allocating space when multiple layers
> +        * are specified. That should be easy since we know that ctx->nr
> +        * >= 1. So we know that ctx->nr - 1 will be correct for the
> +        * base case ctx->nr == 1 and all other cases.
> +        */
> +       len += ctx->nr - 1;
> +       len++; /* and leave room for \0 */
> +       lowerdir = kzalloc(len, GFP_KERNEL_ACCOUNT);
> +       if (!lowerdir)
> +               return ERR_PTR(-ENOMEM);
> +
> +       ofs->config.lowerdir = lowerdir;
> +       for (i = 0; i < ctx->nr; i++) {
> +               l = &ctx->lower[i];
> +
> +               len = strlen(l->name);
> +               memcpy(lowerdir, l->name, len);
> +               if ((ctx->nr > 1) && ((i + 1) != ctx->nr))
> +                       lowerdir[len++] = ':';
> +               lowerdir += len;
>         }
>


I think it might be simpler and cleaner to move the
ctx->lower[i]->name strings as is to layers[i].name after
layers is allocated in ovl_get_layers() below and use a
loop of seq_printf() in ovl_show_options() instead of preparing
the big ofs->config.lowerdir string.

Something to consider.

Thanks,
Amir.

Re: [PATCH v2 2/2] ovl: modify layer parameter parsing

[Christian Brauner]

On Fri, Jun 09, 2023 at 10:52:33PM +0300, Amir Goldstein wrote:
> On Fri, Jun 9, 2023 at 6:42 PM Christian Brauner <brauner@kernel.org> wrote:
> >
> > We ran into issues where mount(8) passed multiple lower layers as one
> > big string through fsconfig(). But the fsconfig() FSCONFIG_SET_STRING
> > option is limited to 256 bytes in strndup_user(). While this would be
> > fixable by extending the fsconfig() buffer I'd rather encourage users to
> > append layers via multiple fsconfig() calls as the interface allows
> > nicely for this. This has also been requested as a feature before.
> >
> > With this port to the new mount api the following will be possible:
> >
> >         fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", "/lower1", 0);
> >
> >         /* set upper layer */
> >         fsconfig(fs_fd, FSCONFIG_SET_STRING, "upperdir", "/upper", 0);
> >
> >         /* append "/lower2", "/lower3", and "/lower4" */
> >         fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", ":/lower2:/lower3:/lower4", 0);
> >
> >         /* turn index feature on */
> >         fsconfig(fs_fd, FSCONFIG_SET_STRING, "index", "on", 0);
> >
> >         /* append "/lower5" */
> >         fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", ":/lower5", 0);
> >
> > Specifying ':' would have been rejected so this isn't a regression. And
> > we can't simply use "lowerdir=/lower" to append on top of existing
> > layers as "lowerdir=/lower,lowerdir=/other-lower" would make
> > "/other-lower" the only lower layer so we'd break uapi if we changed
> > this. So the ':' prefix seems a good compromise.
> >
> > Users can choose to specify multiple layers at once or individual
> > layers. A layer is appended if it starts with ":". This requires that
> > the user has already added at least one layer before. If lowerdir is
> > specified again without a leading ":" then all previous layers are
> > dropped and replaced with the new layers. If lowerdir is specified and
> > empty than all layers are simply dropped.
> >
> > An additional change is that overlayfs will now parse and resolve layers
> > right when they are specified in fsconfig() instead of deferring until
> > super block creation. This allows users to receive early errors.
> >
> > It also allows users to actually use up to 500 layers something which
> > was theoretically possible but ended up not working due to the mount
> > option string passed via mount(2) being too large.
> >
> > This also allows a more privileged process to set config options for a
> > lesser privileged process as the creds for fsconfig() and the creds for
> > fsopen() can differ. We could restrict that they match by enforcing that
> > the creds of fsopen() and fsconfig() match but I don't see why that
> > needs to be the case and allows for a good delegation mechanism.
> >
> > Plus, in the future it means we're able to extend overlayfs mount
> > options and allow users to specify layers via file descriptors instead
> > of paths:
> >
> >         fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower1", dirfd);
> >
> >         /* append */
> >         fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower2", dirfd);
> >
> >         /* append */
> >         fsconfig(FSCONFIG_SET_PATH{_EMPTY}, "lowerdir", "lower3", dirfd);
> >
> >         /* clear all layers specified until now */
> >         fsconfig(FSCONFIG_SET_STRING, "lowerdir", NULL, 0);
> >
> > This would be especially nice if users create an overlayfs mount on top
> > of idmapped layers or just in general private mounts created via
> > open_tree(OPEN_TREE_CLONE). Those mounts would then never have to appear
> > anywhere in the filesystem. But for now just do the minimal thing.
> >
> > We should probably aim to move more validation into ovl_fs_parse_param()
> > so users get errors before fsconfig(FSCONFIG_CMD_CREATE). But that can
> > be done in additional patches later.
> >
> > Link: https://github.com/util-linux/util-linux/issues/2287
> > Link: https://github.com/util-linux/util-linux/issues/1992
> > Link: https://bugs.archlinux.org/task/78702
> > Link: https://lore.kernel.org/linux-unionfs/20230530-klagen-zudem-32c0908c2108@brauner
> > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > ---
> >  fs/overlayfs/Makefile       |   2 +-
> >  fs/overlayfs/layer_params.c | 288 ++++++++++++++++++++++++++++++++++++++
> >  fs/overlayfs/ovl_entry.h    |  30 ++++
> >  fs/overlayfs/super.c        | 328 +++++++++++++++-----------------------------
> >  4 files changed, 431 insertions(+), 217 deletions(-)
> >
> > diff --git a/fs/overlayfs/Makefile b/fs/overlayfs/Makefile
> > index 9164c585eb2f..a3ad81c2e64e 100644
> > --- a/fs/overlayfs/Makefile
> > +++ b/fs/overlayfs/Makefile
> > @@ -6,4 +6,4 @@
> >  obj-$(CONFIG_OVERLAY_FS) += overlay.o
> >
> >  overlay-objs := super.o namei.o util.o inode.o file.o dir.o readdir.o \
> > -               copy_up.o export.o
> > +               copy_up.o export.o layer_params.o
> > diff --git a/fs/overlayfs/layer_params.c b/fs/overlayfs/layer_params.c
> > new file mode 100644
> > index 000000000000..29907afc9d0d
> > --- /dev/null
> > +++ b/fs/overlayfs/layer_params.c
> 
> params.c please
> and please move all the params parsing code here
> not only the layers parsing.
> 
> > @@ -0,0 +1,288 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +
> > +#include <linux/fs.h>
> > +#include <linux/namei.h>
> > +#include <linux/fs_context.h>
> > +#include <linux/fs_parser.h>
> > +#include <linux/posix_acl_xattr.h>
> > +#include <linux/xattr.h>
> > +#include "overlayfs.h"
> > +
> > +static size_t ovl_parse_param_split_lowerdirs(char *str)
> > +{
> > +       size_t ctr = 1;
> > +       char *s, *d;
> > +
> > +       for (s = d = str;; s++, d++) {
> > +               if (*s == '\\') {
> > +                       s++;
> > +               } else if (*s == ':') {
> > +                       *d = '\0';
> > +                       ctr++;
> > +                       continue;
> > +               }
> > +               *d = *s;
> > +               if (!*s)
> > +                       break;
> > +       }
> > +       return ctr;
> > +}
> > +
> > +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;
> > +}
> > +
> > +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;
> > +}
> > +
> > +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;
> > +}
> > +
> > +/*
> > + * Parse lowerdir= mount option:
> > + *
> > + * (1) lowerdir=/lower1:/lower2:/lower3
> > + *     Set "/lower1", "/lower2", and "/lower3" as 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.
> > + */
> > +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;
> > +       size_t nr_lower = 0, nr = 0;
> > +       bool append = false;
> > +
> > +       /* Enforce that users are forced to specify a single ':'. */
> > +       if (strncmp(name, "::", 2) == 0)
> > +               return -EINVAL;
> > +
> > +       /*
> > +        * 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 (*name == ':') {
> > +               /*
> > +                * 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)
> > +                       return -EINVAL;
> > +
> > +               /*
> > +                * Drop the leading. We'll create the final mount option
> > +                * string for the lower layers when we create the superblock.
> > +                */
> > +               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 > 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;
> > +       }
> > +
> > +       /* By (1) and (2) we know nr <= nr_lower <= capacity. */
> > +       dup_iter = dup;
> > +       for (nr = ctx->nr; nr < nr_lower; nr++) {
> > +               l = &ctx->lower[nr];
> > +
> > +               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;
> > +
> > +               dup_iter = strchr(dup_iter, '\0') + 1;
> > +       }
> > +       ctx->nr = nr_lower;
> > +       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;
> > +}
> > diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> > index fd11fe6d6d45..269a9a6f177b 100644
> > --- a/fs/overlayfs/ovl_entry.h
> > +++ b/fs/overlayfs/ovl_entry.h
> > @@ -85,6 +85,36 @@ struct ovl_fs {
> >         errseq_t errseq;
> >  };
> >
> > +#define OVL_MAX_STACK 500
> > +
> > +struct ovl_fs_context_layer {
> > +       char *name;
> > +       struct path path;
> > +};
> > +
> > +/*
> > + * These options imply different behavior when they are explicitly
> > + * specified than when they are left in their default state.
> > + */
> > +#define OVL_METACOPY_SET       BIT(0)
> > +#define OVL_REDIRECT_SET       BIT(1)
> > +#define OVL_NFS_EXPORT_SET     BIT(2)
> > +#define OVL_INDEX_SET          BIT(3)
> > +
> > +struct ovl_fs_context {
> > +       struct path upper;
> > +       struct path work;
> > +       size_t capacity;
> > +       size_t nr;
> > +       u8 set;
> > +       struct ovl_fs_context_layer *lower;
> > +};
> > +
> > +int ovl_parse_param_upperdir(const char *name, struct fs_context *fc,
> > +                            bool workdir);
> > +int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc);
> > +void ovl_parse_param_drop_lowerdir(struct ovl_fs_context *ctx);
> > +
> 
> Please move all this to overlayfs.h.
> I don't think there is a good reason for it to be in this file.
> 
> 
> >  static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)
> >  {
> >         return ofs->layers[0].mnt;
> > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> > index ceaf05743f45..35c61a1d0886 100644
> > --- a/fs/overlayfs/super.c
> > +++ b/fs/overlayfs/super.c
> > @@ -27,8 +27,6 @@ MODULE_LICENSE("GPL");
> >
> >  struct ovl_dir_cache;
> >
> > -#define OVL_MAX_STACK 500
> > -
> >  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,
> > @@ -97,8 +95,11 @@ static const struct constant_table ovl_parameter_xino[] = {
> >         {}
> >  };
> >
> > +#define fsparam_string_empty(NAME, OPT) \
> > +       __fsparam(fs_param_is_string, NAME, OPT, fs_param_can_be_empty, NULL)
> > +
> >  static const struct fs_parameter_spec ovl_parameter_spec[] = {
> > -       fsparam_string("lowerdir",          Opt_lowerdir),
> > +       fsparam_string_empty("lowerdir",    Opt_lowerdir),
> >         fsparam_string("upperdir",          Opt_upperdir),
> >         fsparam_string("workdir",           Opt_workdir),
> >         fsparam_flag("default_permissions", Opt_default_permissions),
> > @@ -113,15 +114,6 @@ static const struct fs_parameter_spec ovl_parameter_spec[] = {
> >         {}
> >  };
> >
> > -#define OVL_METACOPY_SET       BIT(0)
> > -#define OVL_REDIRECT_SET       BIT(1)
> > -#define OVL_NFS_EXPORT_SET     BIT(2)
> > -#define OVL_INDEX_SET          BIT(3)
> > -
> > -struct ovl_fs_context {
> > -       u8 set;
> > -};
> > -
> >  static void ovl_dentry_release(struct dentry *dentry)
> >  {
> >         struct ovl_entry *oe = dentry->d_fsdata;
> > @@ -706,69 +698,6 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> >         goto out_unlock;
> >  }
> >
> > -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_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 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_check_namelen(const struct path *path, struct ovl_fs *ofs,
> >                              const char *name)
> >  {
> > @@ -789,10 +718,6 @@ static int ovl_lower_dir(const char *name, struct path *path,
> >         int fh_type;
> >         int err;
> >
> > -       err = ovl_mount_dir_noesc(name, path);
> > -       if (err)
> > -               return err;
> > -
> >         err = ovl_check_namelen(path, ofs, name);
> >         if (err)
> >                 return err;
> > @@ -841,26 +766,6 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
> >         return ok;
> >  }
> >
> > -static unsigned int ovl_split_lowerdirs(char *str)
> > -{
> > -       unsigned int ctr = 1;
> > -       char *s, *d;
> > -
> > -       for (s = d = str;; s++, d++) {
> > -               if (*s == '\\') {
> > -                       s++;
> > -               } else if (*s == ':') {
> > -                       *d = '\0';
> > -                       ctr++;
> > -                       continue;
> > -               }
> > -               *d = *s;
> > -               if (!*s)
> > -                       break;
> > -       }
> > -       return ctr;
> > -}
> > -
> >  static int ovl_own_xattr_get(const struct xattr_handler *handler,
> >                              struct dentry *dentry, struct inode *inode,
> >                              const char *name, void *buffer, size_t size)
> > @@ -961,15 +866,12 @@ static int ovl_report_in_use(struct ovl_fs *ofs, const char *name)
> >  }
> >
> >  static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
> > -                        struct ovl_layer *upper_layer, struct path *upperpath)
> > +                        struct ovl_layer *upper_layer,
> > +                        const struct path *upperpath)
> >  {
> >         struct vfsmount *upper_mnt;
> >         int err;
> >
> > -       err = ovl_mount_dir(ofs->config.upperdir, upperpath);
> > -       if (err)
> > -               goto out;
> > -
> >         /* Upperdir path should not be r/o */
> >         if (__mnt_is_readonly(upperpath->mnt)) {
> >                 pr_err("upper fs is r/o, try multi-lower layers mount\n");
> > @@ -1256,46 +1158,37 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
> >  }
> >
> >  static int ovl_get_workdir(struct super_block *sb, struct ovl_fs *ofs,
> > -                          const struct path *upperpath)
> > +                          const struct path *upperpath,
> > +                          const struct path *workpath)
> >  {
> >         int err;
> > -       struct path workpath = { };
> > -
> > -       err = ovl_mount_dir(ofs->config.workdir, &workpath);
> > -       if (err)
> > -               goto out;
> >
> >         err = -EINVAL;
> > -       if (upperpath->mnt != workpath.mnt) {
> > +       if (upperpath->mnt != workpath->mnt) {
> >                 pr_err("workdir and upperdir must reside under the same mount\n");
> > -               goto out;
> > +               return err;
> >         }
> > -       if (!ovl_workdir_ok(workpath.dentry, upperpath->dentry)) {
> > +       if (!ovl_workdir_ok(workpath->dentry, upperpath->dentry)) {
> >                 pr_err("workdir and upperdir must be separate subtrees\n");
> > -               goto out;
> > +               return err;
> >         }
> >
> > -       ofs->workbasedir = dget(workpath.dentry);
> > +       ofs->workbasedir = dget(workpath->dentry);
> >
> >         if (ovl_inuse_trylock(ofs->workbasedir)) {
> >                 ofs->workdir_locked = true;
> >         } else {
> >                 err = ovl_report_in_use(ofs, "workdir");
> >                 if (err)
> > -                       goto out;
> > +                       return err;
> >         }
> >
> >         err = ovl_setup_trap(sb, ofs->workbasedir, &ofs->workbasedir_trap,
> >                              "workdir");
> >         if (err)
> > -               goto out;
> > -
> > -       err = ovl_make_workdir(sb, ofs, &workpath);
> > -
> > -out:
> > -       path_put(&workpath);
> > +               return err;
> >
> > -       return err;
> > +       return ovl_make_workdir(sb, ofs, workpath);
> >  }
> >
> >  static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs,
> > @@ -1449,14 +1342,13 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
> >  }
> >
> >  static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> > -                         struct path *stack, unsigned int numlower,
> > -                         struct ovl_layer *layers)
> > +                         struct ovl_fs_context *ctx, struct ovl_layer *layers)
> >  {
> >         int err;
> >         unsigned int i;
> >
> >         err = -ENOMEM;
> > -       ofs->fs = kcalloc(numlower + 1, sizeof(struct ovl_sb), GFP_KERNEL);
> > +       ofs->fs = kcalloc(ctx->nr + 1, sizeof(struct ovl_sb), GFP_KERNEL);
> >         if (ofs->fs == NULL)
> >                 goto out;
> >
> > @@ -1480,12 +1372,13 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> >                 ofs->fs[0].is_lower = false;
> >         }
> >
> > -       for (i = 0; i < numlower; i++) {
> > +       for (i = 0; i < ctx->nr; i++) {
> > +               struct ovl_fs_context_layer *l = &ctx->lower[i];
> >                 struct vfsmount *mnt;
> >                 struct inode *trap;
> >                 int fsid;
> >
> > -               err = fsid = ovl_get_fsid(ofs, &stack[i]);
> > +               err = fsid = ovl_get_fsid(ofs, &l->path);
> >                 if (err < 0)
> >                         goto out;
> >
> > @@ -1496,11 +1389,11 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> >                  * the upperdir/workdir is in fact in-use by our
> >                  * upperdir/workdir.
> >                  */
> > -               err = ovl_setup_trap(sb, stack[i].dentry, &trap, "lowerdir");
> > +               err = ovl_setup_trap(sb, l->path.dentry, &trap, "lowerdir");
> >                 if (err)
> >                         goto out;
> >
> > -               if (ovl_is_inuse(stack[i].dentry)) {
> > +               if (ovl_is_inuse(l->path.dentry)) {
> >                         err = ovl_report_in_use(ofs, "lowerdir");
> >                         if (err) {
> >                                 iput(trap);
> > @@ -1508,7 +1401,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> >                         }
> >                 }
> >
> > -               mnt = clone_private_mount(&stack[i]);
> > +               mnt = clone_private_mount(&l->path);
> >                 err = PTR_ERR(mnt);
> >                 if (IS_ERR(mnt)) {
> >                         pr_err("failed to clone lowerpath\n");
> > @@ -1569,63 +1462,86 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> >  }
> >
> >  static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> > -                               const char *lower, unsigned int numlower,
> > -                               struct ovl_fs *ofs, struct ovl_layer *layers)
> > +                                           struct ovl_fs_context *ctx,
> > +                                           struct ovl_fs *ofs,
> > +                                           struct ovl_layer *layers)
> >  {
> >         int err;
> > -       struct path *stack = NULL;
> >         unsigned int i;
> >         struct ovl_entry *oe;
> > +       size_t len;
> > +       char *lowerdir;
> > +       struct ovl_fs_context_layer *l;
> >
> > -       if (!ofs->config.upperdir && numlower == 1) {
> > +       if (!ofs->config.upperdir && ctx->nr == 1) {
> >                 pr_err("at least 2 lowerdir are needed while upperdir nonexistent\n");
> >                 return ERR_PTR(-EINVAL);
> >         }
> >
> > -       stack = kcalloc(numlower, sizeof(struct path), GFP_KERNEL);
> > -       if (!stack)
> > -               return ERR_PTR(-ENOMEM);
> > -
> >         err = -EINVAL;
> > -       for (i = 0; i < numlower; i++) {
> > -               err = ovl_lower_dir(lower, &stack[i], ofs, &sb->s_stack_depth);
> > +       len = 0;
> > +       for (i = 0; i < ctx->nr; i++) {
> > +               l = &ctx->lower[i];
> > +
> > +               err = ovl_lower_dir(l->name, &l->path, ofs, &sb->s_stack_depth);
> >                 if (err)
> > -                       goto out_err;
> > +                       return ERR_PTR(err);
> >
> > -               lower = strchr(lower, '\0') + 1;
> > +               len += strlen(l->name);
> >         }
> >
> >         err = -EINVAL;
> >         sb->s_stack_depth++;
> >         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
> >                 pr_err("maximum fs stacking depth exceeded\n");
> > -               goto out_err;
> > +               return ERR_PTR(err);
> > +       }
> .> +
> > +       /*
> > +        * Create a string of all lower layers that we store in
> > +        * ofs->config.lowerdir which we can display to userspace in
> > +        * mount options. For example, this assembles "/lower1",
> > +        * "/lower2" into "/lower1:/lower2".
> > +        *
> > +        * We need to make sure we add a ':'. Thus, we need to account
> > +        * for the separators when allocating space when multiple layers
> > +        * are specified. That should be easy since we know that ctx->nr
> > +        * >= 1. So we know that ctx->nr - 1 will be correct for the
> > +        * base case ctx->nr == 1 and all other cases.
> > +        */
> > +       len += ctx->nr - 1;
> > +       len++; /* and leave room for \0 */
> > +       lowerdir = kzalloc(len, GFP_KERNEL_ACCOUNT);
> > +       if (!lowerdir)
> > +               return ERR_PTR(-ENOMEM);
> > +
> > +       ofs->config.lowerdir = lowerdir;
> > +       for (i = 0; i < ctx->nr; i++) {
> > +               l = &ctx->lower[i];
> > +
> > +               len = strlen(l->name);
> > +               memcpy(lowerdir, l->name, len);
> > +               if ((ctx->nr > 1) && ((i + 1) != ctx->nr))
> > +                       lowerdir[len++] = ':';
> > +               lowerdir += len;
> >         }
> >
> 
> 
> I think it might be simpler and cleaner to move the
> ctx->lower[i]->name strings as is to layers[i].name after
> layers is allocated in ovl_get_layers() below and use a
> loop of seq_printf() in ovl_show_options() instead of preparing
> the big ofs->config.lowerdir string.
> 
> Something to consider.

Works for me. I'll try that out.

Re: [PATCH v2 0/2] ovl: port to new mount api & updated layer parsing

[Amir Goldstein]

On Fri, Jun 9, 2023 at 6:42 PM Christian Brauner <brauner@kernel.org> wrote:
>
> Hey everyone,
>
> This ports overlayfs to the new mount api and modifies layer parsing to
> allow for additive layer specification via fsconfig().
>
> I'm not sure if I need to rebase the changes on top of Amir's lazy
> lookup. If so, please let me know!

Yes, please.

I look at the conflicts and they don't look so bad.
I think only need to figure out numlowerdata during parsing
which should be pretty easy and then the entire wacky loop
to figure out numlowerdata in ovl_get_lowerstack() can be nuked.
all the rest stays the same.

Thanks,
Amir.