linux-kernel - Re: [PATCH] exfat: add ioctls for accessing attributes

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Message-ID: <CAKYAXd8xsszN7NOe8bL-PCEsy3X2Y3FkOfSX1ETMKbH05xmUBg@mail.gmail.com>
Date:   Thu, 24 Aug 2023 21:50:56 +0900
From:   Namjae Jeon <linkinjeon@...nel.org>
To:     Jan Cincera <hcincera@...il.com>
Cc:     Sungjong Seo <sj1557.seo@...sung.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exfat: add ioctls for accessing attributes

2023-08-16 3:29 GMT+09:00, Jan Cincera <hcincera@...il.com>:
> 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@...il.com>
> ---
>  fs/exfat/exfat_fs.h |  6 +++
>  fs/exfat/file.c     | 97 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 103 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)
> +
>  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..b358acbead27 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 +318,96 @@ 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);
> +
> +	/*
> +	 * ATTR_VOLUME and ATTR_SUBDIR cannot be changed; this also
> +	 * prevents the user from turning us into a VFAT
> +	 * longname entry.  Also, we obviously can't set
> +	 * any of the NTFS attributes in the high 24 bits.
> +	 */
This comments seems to be wrong. In particular, The comment about
longfilename and ATTR_VOLUME for vfat should be removed.

> +	attr &= 0xff & ~(ATTR_VOLUME | ATTR_SUBDIR);
> +	/* Merge in ATTR_VOLUME and ATTR_DIR */
> +	attr |= (EXFAT_I(inode)->attr & ATTR_VOLUME) |
> +		(is_dir ? ATTR_SUBDIR : 0);
We need to mask exfat file attribute bits like the following not to
set reserved fields(+ ATTR_SUBDIR). And there is no ATTR_VOLUME field
in exfat.

Table 28 FileAttributes Field Structure
ReadOnly        0	1	This field is mandatory and conforms to the MS-DOS
definition.
Hidden             1     	1	This field is mandatory and conforms to
the MS-DOS definition.
System            2	1	This field is mandatory and conforms to the
MS-DOS definition.
Reserved1       3	1	This field is mandatory and its contents are reserved.
Directory          4	1	This field is mandatory and conforms to the
MS-DOS definition.
Archive            5	1	This field is mandatory and conforms to the
MS-DOS definition.
Reserved2	6	10	This field is mandatory and its contents are reserved.

Thanks.