linux-kernel - Re: [PATCH v3 2/2] fs: fat: add ioctl method in fat filesystem driver

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Date:   Sat, 23 Dec 2017 19:23:27 +0900
From:   OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:     Chen Guanqiao <chen.chenchacha@...mail.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] fs: fat: add ioctl method in fat filesystem driver

Chen Guanqiao <chen.chenchacha@...mail.com> writes:

> +static int fat_check_volume_label(const char *label)
> +{
> +	int i;
> +
> +	for (i=0; i<11; ++i) {
> +		switch (label[i]) {
> +		case 0x20:
> +		case 'A' ... 'Z':
> +		case '0' ... '9':
> +			continue;
> +		case 0:
> +			return 0;
> +		default:
> +			return -EINVAL;
> +		}
> +	}
> +	return -EINVAL;
> +}

This check is really work? Especially what Windows show if '\0' is
included in label?

> +static int fat_ioctl_get_volume_label(struct inode *inode,
> +				      u8 __user *vol_label)
> +{
> +	int ret = 0;
> +	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
> +
> +	if (copy_to_user(vol_label, sbi->vol_label, sizeof(sbi->vol_label)))
> +		ret = -EFAULT;
> +
> +	return ret;
> +}

This should handle the label in root dir too.

> +	inode_lock(inode);

Lock is not enough.

> +	if (sb_rdonly(inode->i_sb)) {
> +		err = -EROFS;
> +		goto out_unlock_inode;
> +	}

mnt_want_write_file() checks it already.

> +	/* handling sector's vol_label */
> +	bh = sb_bread(inode->i_sb, 0);
> +	if (bh == NULL) {
> +		fat_msg(inode->i_sb, KERN_ERR,
> +			"unable to read boot sector to write volume label");
> +		err = -EFAULT;

-EIO

> +	if (b->fat16.signature == 0x28 || b->fat32.signature == 0x28) {
> +		fat_msg(inode->i_sb, KERN_ERR,
> +			"volume label supported since OS/2 1.2 and MS-DOS 4.0 "
> +			"and higher");
> +		err = -EFAULT;
> +		goto out_unlock_inode;
> +	}

I don't know though, is this check necessary?

> +	/* handling root directory's vol_label */
> +	bh = sb_bread(sb, sbi->dir_start);
> +	entry = &((struct msdos_dir_entry *)(bh->b_data))[0];
> +
> +	lock_buffer(bh);
> +	memcpy(entry->name, label, sizeof(entry->name));
> +	mark_buffer_dirty(bh);
> +	unlock_buffer(bh);
> +	brelse(bh);

This totally doesn't work. Please check other implementations how to
handle label.

> + out_unlock_inode:
> +	inode_unlock(inode);

Missing release mnt_want_write_file().

Thanks.