Re: [PATCH v2 3/9] mm/mshare: make msharefs writable and support directories

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Jun 29, 2022 at 04:53:54PM -0600, Khalid Aziz wrote:
> Make msharefs filesystem writable and allow creating directories
> to support better access control to mshare'd regions defined in
> msharefs.
> 
> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
> ---
>  mm/mshare.c | 195 +++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 186 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/mshare.c b/mm/mshare.c
> index 3e448e11c742..2d5924d39221 100644
> --- a/mm/mshare.c
> +++ b/mm/mshare.c
> @@ -21,11 +21,21 @@
>  #include <linux/fileattr.h>
>  #include <uapi/linux/magic.h>
>  #include <uapi/linux/limits.h>
> +#include <uapi/linux/mman.h>
>  
>  static struct super_block *msharefs_sb;
>  
> +static const struct inode_operations msharefs_dir_inode_ops;
> +static const struct inode_operations msharefs_file_inode_ops;
> +
> +static int
> +msharefs_open(struct inode *inode, struct file *file)
> +{
> +	return simple_open(inode, file);
> +}
> +
>  static const struct file_operations msharefs_file_operations = {
> -	.open		= simple_open,
> +	.open		= msharefs_open,
>  	.llseek		= no_llseek,
>  };
>  
> @@ -42,6 +52,113 @@ msharefs_d_hash(const struct dentry *dentry, struct qstr *qstr)
>  	return 0;
>  }
>  
> +static struct dentry
> +*msharefs_alloc_dentry(struct dentry *parent, const char *name)
> +{
> +	struct dentry *d;
> +	struct qstr q;
> +	int err;
> +
> +	q.name = name;
> +	q.len = strlen(name);
> +
> +	err = msharefs_d_hash(parent, &q);
> +	if (err)
> +		return ERR_PTR(err);
> +
> +	d = d_alloc(parent, &q);
> +	if (d)
> +		return d;
> +
> +	return ERR_PTR(-ENOMEM);
> +}
> +
> +static struct inode
> +*msharefs_get_inode(struct super_block *sb, const struct inode *dir,
> +			umode_t mode)
> +{
> +	struct inode *inode = new_inode(sb);
> +
> +	if (inode) {

Not sure why you wouldn't go with the less-indently version:

	if (!inode)
		return ERR_PTR(-ENOMEM);

	inode->i_ino = get_next_ino();
	<etc>

> +		inode->i_ino = get_next_ino();
> +		inode_init_owner(&init_user_ns, inode, dir, mode);
> +
> +		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
> +
> +		switch (mode & S_IFMT) {

Shouldn't we set the mode somewhere?

> +		case S_IFREG:
> +			inode->i_op = &msharefs_file_inode_ops;
> +			inode->i_fop = &msharefs_file_operations;
> +			break;
> +		case S_IFDIR:
> +			inode->i_op = &msharefs_dir_inode_ops;
> +			inode->i_fop = &simple_dir_operations;
> +			inc_nlink(inode);
> +			break;
> +		case S_IFLNK:
> +			inode->i_op = &page_symlink_inode_operations;
> +			break;
> +		default:
> +			discard_new_inode(inode);
> +			inode = NULL;
> +			break;
> +		}
> +	}
> +
> +	return inode;
> +}
> +
> +static int
> +msharefs_mknod(struct user_namespace *mnt_userns, struct inode *dir,
> +		struct dentry *dentry, umode_t mode, dev_t dev)
> +{
> +	struct inode *inode;
> +	int err = 0;
> +
> +	inode = msharefs_get_inode(dir->i_sb, dir, mode);
> +	if (IS_ERR(inode))
> +		return PTR_ERR(inode);

...and if @inode is NULL?

> +
> +	d_instantiate(dentry, inode);
> +	dget(dentry);
> +	dir->i_mtime = dir->i_ctime = current_time(dir);
> +
> +	return err;
> +}
> +
> +static int
> +msharefs_create(struct user_namespace *mnt_userns, struct inode *dir,
> +		struct dentry *dentry, umode_t mode, bool excl)
> +{
> +	return msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFREG, 0);
> +}
> +
> +static int
> +msharefs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
> +		struct dentry *dentry, umode_t mode)
> +{
> +	int ret = msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFDIR, 0);
> +
> +	if (!ret)
> +		inc_nlink(dir);
> +	return ret;
> +}
> +
> +static const struct inode_operations msharefs_file_inode_ops = {
> +	.setattr	= simple_setattr,
> +	.getattr	= simple_getattr,
> +};
> +static const struct inode_operations msharefs_dir_inode_ops = {
> +	.create		= msharefs_create,
> +	.lookup		= simple_lookup,
> +	.link		= simple_link,
> +	.unlink		= simple_unlink,
> +	.mkdir		= msharefs_mkdir,
> +	.rmdir		= simple_rmdir,
> +	.mknod		= msharefs_mknod,
> +	.rename		= simple_rename,
> +};
> +
>  static void
>  mshare_evict_inode(struct inode *inode)
>  {
> @@ -58,7 +175,7 @@ mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
>  {
>  	char s[80];
>  
> -	sprintf(s, "%ld", PGDIR_SIZE);
> +	sprintf(s, "%ld\n", PGDIR_SIZE);

Changing this already?

>  	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
>  }
>  
> @@ -72,6 +189,38 @@ static const struct super_operations mshare_s_ops = {
>  	.evict_inode = mshare_evict_inode,
>  };
>  
> +static int
> +prepopulate_files(struct super_block *s, struct inode *dir,
> +			struct dentry *root, const struct tree_descr *files)
> +{
> +	int i;
> +	struct inode *inode;
> +	struct dentry *dentry;
> +
> +	for (i = 0; !files->name || files->name[0]; i++, files++) {
> +		if (!files->name)
> +			continue;

What ends the array?  NULL name or empty name?
Do we have to erase all of these when the fs gets unmounted?

--D

> +
> +		dentry = msharefs_alloc_dentry(root, files->name);
> +		if (!dentry)
> +			return -ENOMEM;
> +
> +		inode = msharefs_get_inode(s, dir, S_IFREG | files->mode);
> +		if (!inode) {
> +			dput(dentry);
> +			return -ENOMEM;
> +		}
> +		inode->i_mode = S_IFREG | files->mode;
> +		inode->i_atime = inode->i_mtime = inode->i_ctime
> +			= current_time(inode);
> +		inode->i_fop = files->ops;
> +		inode->i_ino = i;
> +		d_add(dentry, inode);
> +	}
> +
> +	return 0;
> +}
> +
>  static int
>  msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
>  {
> @@ -79,21 +228,49 @@ msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
>  		[2] = { "mshare_info", &mshare_info_ops, 0444},
>  		{""},
>  	};
> -	int err;
> +	struct inode *inode;
> +	struct dentry *root;
> +	int err = 0;
>  
> -	err = simple_fill_super(sb, MSHARE_MAGIC, mshare_files);
> -	if (!err) {
> -		msharefs_sb = sb;
> -		sb->s_d_op = &msharefs_d_ops;
> -		sb->s_op = &mshare_s_ops;
> +	sb->s_blocksize		= PAGE_SIZE;
> +	sb->s_blocksize_bits	= PAGE_SHIFT;
> +	sb->s_magic		= MSHARE_MAGIC;
> +	sb->s_op		= &mshare_s_ops;
> +	sb->s_d_op		= &msharefs_d_ops;
> +	sb->s_time_gran		= 1;
> +
> +	inode = msharefs_get_inode(sb, NULL, S_IFDIR | 0777);
> +	if (!inode) {
> +		err = -ENOMEM;
> +		goto out;
>  	}
> +	inode->i_ino = 1;
> +	root = d_make_root(inode);
> +	if (!root) {
> +		err = -ENOMEM;
> +		goto out;
> +	}
> +
> +	err = prepopulate_files(sb, inode, root, mshare_files);
> +	if (err < 0)
> +		goto clean_root;
> +
> +	sb->s_root = root;
> +	msharefs_sb = sb;
> +	return err;
> +
> +clean_root:
> +	d_genocide(root);
> +	shrink_dcache_parent(root);
> +	dput(root);
> +out:
>  	return err;
>  }
>  
>  static int
>  msharefs_get_tree(struct fs_context *fc)
>  {
> -	return get_tree_single(fc, msharefs_fill_super);
> +	return get_tree_nodev(fc, msharefs_fill_super);
>  }
>  
>  static const struct fs_context_operations msharefs_context_ops = {
> -- 
> 2.32.0
>