Re: [PATCH v2] exfat: add ioctls for accessing attributes

[Darrick J. Wong]

On Sun, Aug 27, 2023 at 12:42:07PM +0200, Jan Cincera wrote:
> Add GET and SET attributes ioctls to enable attribute modification.
> We already do this in FAT and a few userspace utils made for it would
> benefit from this also working on exFAT, namely fatattr.
> 
> Signed-off-by: Jan Cincera <hcincera@xxxxxxxxx>
> ---
> Changes in v2:
>   - Removed irrelevant comments.
>   - Now masking reserved fields.
> 
>  fs/exfat/exfat_fs.h |  6 +++
>  fs/exfat/file.c     | 93 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 99 insertions(+)
> 
> diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
> index 729ada9e26e8..ebe8c4b928f4 100644
> --- a/fs/exfat/exfat_fs.h
> +++ b/fs/exfat/exfat_fs.h
> @@ -149,6 +149,12 @@ enum {
>  #define DIR_CACHE_SIZE		\
>  	(DIV_ROUND_UP(EXFAT_DEN_TO_B(ES_MAX_ENTRY_NUM), SECTOR_SIZE) + 1)
>  
> +/*
> + * attribute ioctls, same as their FAT equivalents.
> + */
> +#define EXFAT_IOCTL_GET_ATTRIBUTES	_IOR('r', 0x10, __u32)
> +#define EXFAT_IOCTL_SET_ATTRIBUTES	_IOW('r', 0x11, __u32)

Can you reuse the definitions from include/uapi/linux/msdos_fs.h instead
of redefining them here?

Otherwise this looks like a mostly straight port of the fs/fat/
versions of these functions.

--D

> +
>  struct exfat_dentry_namebuf {
>  	char *lfn;
>  	int lfnbuf_len; /* usually MAX_UNINAME_BUF_SIZE */
> diff --git a/fs/exfat/file.c b/fs/exfat/file.c
> index 3cbd270e0cba..b31ce0868ddd 100644
> --- a/fs/exfat/file.c
> +++ b/fs/exfat/file.c
> @@ -8,6 +8,8 @@
>  #include <linux/cred.h>
>  #include <linux/buffer_head.h>
>  #include <linux/blkdev.h>
> +#include <linux/fsnotify.h>
> +#include <linux/security.h>
>  
>  #include "exfat_raw.h"
>  #include "exfat_fs.h"
> @@ -316,6 +318,92 @@ int exfat_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>  	return error;
>  }
>  
> +/*
> + * modified ioctls from fat/file.c by Welmer Almesberger
> + */
> +static int exfat_ioctl_get_attributes(struct inode *inode, u32 __user *user_attr)
> +{
> +	u32 attr;
> +
> +	inode_lock_shared(inode);
> +	attr = exfat_make_attr(inode);
> +	inode_unlock_shared(inode);
> +
> +	return put_user(attr, user_attr);
> +}
> +
> +static int exfat_ioctl_set_attributes(struct file *file, u32 __user *user_attr)
> +{
> +	struct inode *inode = file_inode(file);
> +	struct exfat_sb_info *sbi = EXFAT_SB(inode->i_sb);
> +	int is_dir = S_ISDIR(inode->i_mode);
> +	u32 attr, oldattr;
> +	struct iattr ia;
> +	int err;
> +
> +	err = get_user(attr, user_attr);
> +	if (err)
> +		goto out;
> +
> +	err = mnt_want_write_file(file);
> +	if (err)
> +		goto out;
> +	inode_lock(inode);
> +
> +	oldattr = exfat_make_attr(inode);
> +
> +	/*
> +	 * Mask attributes so we don't set reserved fields.
> +	 */
> +	attr &= (ATTR_READONLY | ATTR_HIDDEN | ATTR_SYSTEM | ATTR_ARCHIVE);
> +	attr |= (is_dir ? ATTR_SUBDIR : 0);
> +
> +	/* Equivalent to a chmod() */
> +	ia.ia_valid = ATTR_MODE | ATTR_CTIME;
> +	ia.ia_ctime = current_time(inode);
> +	if (is_dir)
> +		ia.ia_mode = exfat_make_mode(sbi, attr, 0777);
> +	else
> +		ia.ia_mode = exfat_make_mode(sbi, attr, 0666 | (inode->i_mode & 0111));
> +
> +	/* The root directory has no attributes */
> +	if (inode->i_ino == EXFAT_ROOT_INO && attr != ATTR_SUBDIR) {
> +		err = -EINVAL;
> +		goto out_unlock_inode;
> +	}
> +
> +	if (((attr | oldattr) & ATTR_SYSTEM) &&
> +	    !capable(CAP_LINUX_IMMUTABLE)) {
> +		err = -EPERM;
> +		goto out_unlock_inode;
> +	}
> +
> +	/*
> +	 * The security check is questionable...  We single
> +	 * out the RO attribute for checking by the security
> +	 * module, just because it maps to a file mode.
> +	 */
> +	err = security_inode_setattr(file_mnt_idmap(file),
> +				     file->f_path.dentry, &ia);
> +	if (err)
> +		goto out_unlock_inode;
> +
> +	/* This MUST be done before doing anything irreversible... */
> +	err = exfat_setattr(file_mnt_idmap(file), file->f_path.dentry, &ia);
> +	if (err)
> +		goto out_unlock_inode;
> +
> +	fsnotify_change(file->f_path.dentry, ia.ia_valid);
> +
> +	exfat_save_attr(inode, attr);
> +	mark_inode_dirty(inode);
> +out_unlock_inode:
> +	inode_unlock(inode);
> +	mnt_drop_write_file(file);
> +out:
> +	return err;
> +}
> +
>  static int exfat_ioctl_fitrim(struct inode *inode, unsigned long arg)
>  {
>  	struct fstrim_range range;
> @@ -346,8 +434,13 @@ static int exfat_ioctl_fitrim(struct inode *inode, unsigned long arg)
>  long exfat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  {
>  	struct inode *inode = file_inode(filp);
> +	u32 __user *user_attr = (u32 __user *)arg;
>  
>  	switch (cmd) {
> +	case EXFAT_IOCTL_GET_ATTRIBUTES:
> +		return exfat_ioctl_get_attributes(inode, user_attr);
> +	case EXFAT_IOCTL_SET_ATTRIBUTES:
> +		return exfat_ioctl_set_attributes(filp, user_attr);
>  	case FITRIM:
>  		return exfat_ioctl_fitrim(inode, arg);
>  	default:
> -- 
> 2.40.1