Date:   Mon, 23 Aug 2021 06:51:50 +0300
From:   Kari Argillander <kari.argillander@...il.com>
To:     Pali Rohár <pali@...nel.org>
Cc:     linux-fsdevel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net, linux-cifs@...r.kernel.org,
        jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Luis de Bethencourt <luisbg@...nel.org>,
        Salah Triki <salah.triki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Kleikamp <shaggy@...nel.org>,
        Anton Altaparmakov <anton@...era.com>,
        Pavel Machek <pavel@....cz>,
        Marek Behún <marek.behun@....cz>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC PATCH 01/20] fat: Fix iocharset=utf8 mount option

On Sun, Aug 08, 2021 at 06:24:34PM +0200, Pali Rohár wrote:
> Currently iocharset=utf8 mount option is broken and error is printed to
> dmesg when it is used. To use UTF-8 as iocharset, it is required to use
> utf8=1 mount option.
> 
> Fix iocharset=utf8 mount option to use be equivalent to the utf8=1 mount
> option and remove printing error from dmesg.
> 
> FAT by definition is case-insensitive but current Linux implementation is
> case-sensitive for non-ASCII characters when UTF-8 is used. This patch does
> not change this UTF-8 behavior. Only more comments in fat_utf8_strnicmp()
> function are added about it.
> 
> After this patch iocharset=utf8 starts working, so there is no need to have
> separate config option FAT_DEFAULT_UTF8 as FAT_DEFAULT_IOCHARSET for utf8
> also starts working. So remove redundant config option FAT_DEFAULT_UTF8.
> 
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>  fs/fat/Kconfig      | 15 ---------------
>  fs/fat/dir.c        | 17 +++++++----------
>  fs/fat/fat.h        | 22 ++++++++++++++++++++++
>  fs/fat/inode.c      | 28 +++++++++++-----------------
>  fs/fat/namei_vfat.c | 26 +++++++++++++++++++-------
>  5 files changed, 59 insertions(+), 49 deletions(-)
> 
> diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig
> index 66532a71e8fd..a31594137d5e 100644
> --- a/fs/fat/Kconfig
> +++ b/fs/fat/Kconfig
> @@ -100,18 +100,3 @@ config FAT_DEFAULT_IOCHARSET
>  
>  	  Enable any character sets you need in File Systems/Native Language
>  	  Support.
> -
> -config FAT_DEFAULT_UTF8
> -	bool "Enable FAT UTF-8 option by default"
> -	depends on VFAT_FS
> -	default n
> -	help
> -	  Set this if you would like to have "utf8" mount option set
> -	  by default when mounting FAT filesystems.
> -
> -	  Even if you say Y here can always disable UTF-8 for
> -	  particular mount by adding "utf8=0" to mount options.
> -
> -	  Say Y if you use UTF-8 encoding for file names, N otherwise.
> -
> -	  See <file:Documentation/filesystems/vfat.rst> for more information.
> diff --git a/fs/fat/dir.c b/fs/fat/dir.c
> index c4a274285858..49fe8dc6e5f0 100644
> --- a/fs/fat/dir.c
> +++ b/fs/fat/dir.c
> @@ -33,11 +33,6 @@
>  #define FAT_MAX_UNI_CHARS	((MSDOS_SLOTS - 1) * 13 + 1)
>  #define FAT_MAX_UNI_SIZE	(FAT_MAX_UNI_CHARS * sizeof(wchar_t))
>  
> -static inline unsigned char fat_tolower(unsigned char c)
> -{
> -	return ((c >= 'A') && (c <= 'Z')) ? c+32 : c;
> -}
> -
>  static inline loff_t fat_make_i_pos(struct super_block *sb,
>  				    struct buffer_head *bh,
>  				    struct msdos_dir_entry *de)
> @@ -258,10 +253,12 @@ static inline int fat_name_match(struct msdos_sb_info *sbi,
>  	if (a_len != b_len)
>  		return 0;
>  
> -	if (sbi->options.name_check != 's')
> -		return !nls_strnicmp(sbi->nls_io, a, b, a_len);
> -	else
> +	if (sbi->options.name_check == 's')
>  		return !memcmp(a, b, a_len);
> +	else if (sbi->options.utf8)
> +		return !fat_utf8_strnicmp(a, b, a_len);
> +	else
> +		return !nls_strnicmp(sbi->nls_io, a, b, a_len);
>  }
>  
>  enum { PARSE_INVALID = 1, PARSE_NOT_LONGNAME, PARSE_EOF, };
> @@ -384,7 +381,7 @@ static int fat_parse_short(struct super_block *sb,
>  					de->lcase & CASE_LOWER_BASE);
>  		if (chl <= 1) {
>  			if (!isvfat)
> -				ptname[i] = nocase ? c : fat_tolower(c);
> +				ptname[i] = nocase ? c : fat_ascii_to_lower(c);
>  			i++;
>  			if (c != ' ') {
>  				name_len = i;
> @@ -421,7 +418,7 @@ static int fat_parse_short(struct super_block *sb,
>  		if (chl <= 1) {
>  			k++;
>  			if (!isvfat)
> -				ptname[i] = nocase ? c : fat_tolower(c);
> +				ptname[i] = nocase ? c : fat_ascii_to_lower(c);
>  			i++;
>  			if (c != ' ') {
>  				name_len = i;
> diff --git a/fs/fat/fat.h b/fs/fat/fat.h
> index 02d4d4234956..0cd15fb3b042 100644
> --- a/fs/fat/fat.h
> +++ b/fs/fat/fat.h
> @@ -310,6 +310,28 @@ static inline void fatwchar_to16(__u8 *dst, const wchar_t *src, size_t len)
>  #endif
>  }
>  
> +static inline unsigned char fat_ascii_to_lower(unsigned char c)
> +{
> +	return ((c >= 'A') && (c <= 'Z')) ? c+32 : c;
> +}
> +
> +static inline int fat_utf8_strnicmp(const unsigned char *a,
> +				    const unsigned char *b,
> +				    int len)
> +{
> +	int i;
> +
> +	/*
> +	 * FIXME: UTF-8 doesn't provide FAT semantics
> +	 * Case-insensitive support is only for 7-bit ASCII characters
> +	 */
> +	for (i = 0; i < len; i++) {
> +		if (fat_ascii_to_lower(a[i]) != fat_ascii_to_lower(b[i]))
> +			return 1;
> +	}
> +	return 0;
> +}
> +
>  /* fat/cache.c */
>  extern void fat_cache_inval_inode(struct inode *inode);
>  extern int fat_get_cluster(struct inode *inode, int cluster,
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index de0c9b013a85..f8c8a739f8f0 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -957,7 +957,9 @@ static int fat_show_options(struct seq_file *m, struct dentry *root)
>  		/* strip "cp" prefix from displayed option */
>  		seq_printf(m, ",codepage=%s", &sbi->nls_disk->charset[2]);
>  	if (isvfat) {
> -		if (sbi->nls_io)
> +		if (opts->utf8)
> +			seq_printf(m, ",iocharset=utf8");

checkpatch will probably warn you about this.

WARNING: Prefer seq_puts to seq_printf

> +		else if (sbi->nls_io)
>  			seq_printf(m, ",iocharset=%s", sbi->nls_io->charset);
>  
>  		switch (opts->shortname) {
> @@ -994,8 +996,6 @@ static int fat_show_options(struct seq_file *m, struct dentry *root)
>  		if (opts->nocase)
>  			seq_puts(m, ",nocase");
>  	} else {
> -		if (opts->utf8)
> -			seq_puts(m, ",utf8");
>  		if (opts->unicode_xlate)
>  			seq_puts(m, ",uni_xlate");
>  		if (!opts->numtail)
> @@ -1157,8 +1157,6 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
>  	opts->errors = FAT_ERRORS_RO;
>  	*debug = 0;
>  
> -	opts->utf8 = IS_ENABLED(CONFIG_FAT_DEFAULT_UTF8) && is_vfat;
> -
>  	if (!options)
>  		goto out;
>  
> @@ -1319,10 +1317,14 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
>  					| VFAT_SFN_CREATE_WIN95;
>  			break;
>  		case Opt_utf8_no:		/* 0 or no or false */
> -			opts->utf8 = 0;
> +			fat_reset_iocharset(opts);
>  			break;
>  		case Opt_utf8_yes:		/* empty or 1 or yes or true */
> -			opts->utf8 = 1;
> +			fat_reset_iocharset(opts);
> +			iocharset = kstrdup("utf8", GFP_KERNEL);
> +			if (!iocharset)
> +				return -ENOMEM;
> +			opts->iocharset = iocharset;
>  			break;
>  		case Opt_uni_xl_no:		/* 0 or no or false */
>  			opts->unicode_xlate = 0;
> @@ -1360,18 +1362,11 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
>  	}
>  
>  out:
> -	/* UTF-8 doesn't provide FAT semantics */
> -	if (!strcmp(opts->iocharset, "utf8")) {
> -		fat_msg(sb, KERN_WARNING, "utf8 is not a recommended IO charset"
> -		       " for FAT filesystems, filesystem will be "
> -		       "case sensitive!");
> -	}
> +	opts->utf8 = !strcmp(opts->iocharset, "utf8") && is_vfat;
>  
>  	/* If user doesn't specify allow_utime, it's initialized from dmask. */
>  	if (opts->allow_utime == (unsigned short)-1)
>  		opts->allow_utime = ~opts->fs_dmask & (S_IWGRP | S_IWOTH);
> -	if (opts->unicode_xlate)
> -		opts->utf8 = 0;
>  	if (opts->nfs == FAT_NFS_NOSTALE_RO) {
>  		sb->s_flags |= SB_RDONLY;
>  		sb->s_export_op = &fat_export_ops_nostale;
> @@ -1832,8 +1827,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
>  		goto out_fail;
>  	}
>  
> -	/* FIXME: utf8 is using iocharset for upper/lower conversion */
> -	if (sbi->options.isvfat) {
> +	if (sbi->options.isvfat && !sbi->options.utf8) {
>  		sbi->nls_io = load_nls(sbi->options.iocharset);
>  		if (!sbi->nls_io) {
>  			fat_msg(sb, KERN_ERR, "IO charset %s not found",
> diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
> index 5369d82e0bfb..efb3cb9ea8a8 100644
> --- a/fs/fat/namei_vfat.c
> +++ b/fs/fat/namei_vfat.c
> @@ -134,6 +134,7 @@ static int vfat_hash(const struct dentry *dentry, struct qstr *qstr)
>  static int vfat_hashi(const struct dentry *dentry, struct qstr *qstr)
>  {
>  	struct nls_table *t = MSDOS_SB(dentry->d_sb)->nls_io;
> +	int utf8 = MSDOS_SB(dentry->d_sb)->options.utf8;
>  	const unsigned char *name;
>  	unsigned int len;
>  	unsigned long hash;
> @@ -142,8 +143,17 @@ static int vfat_hashi(const struct dentry *dentry, struct qstr *qstr)
>  	len = vfat_striptail_len(qstr);
>  
>  	hash = init_name_hash(dentry);
> -	while (len--)
> -		hash = partial_name_hash(nls_tolower(t, *name++), hash);
> +	if (utf8) {
> +		/*
> +		 * FIXME: UTF-8 doesn't provide FAT semantics
> +		 * Case-insensitive support is only for 7-bit ASCII characters
> +		 */
> +		while (len--)
> +			hash = partial_name_hash(fat_ascii_to_lower(*name++), hash);
> +	} else {
> +		while (len--)
> +			hash = partial_name_hash(nls_tolower(t, *name++), hash);
> +	}
>  	qstr->hash = end_name_hash(hash);
>  
>  	return 0;
> @@ -156,16 +166,18 @@ static int vfat_cmpi(const struct dentry *dentry,
>  		unsigned int len, const char *str, const struct qstr *name)
>  {
>  	struct nls_table *t = MSDOS_SB(dentry->d_sb)->nls_io;
> +	int utf8 = MSDOS_SB(dentry->d_sb)->options.utf8;
>  	unsigned int alen, blen;
>  
>  	/* A filename cannot end in '.' or we treat it like it has none */
>  	alen = vfat_striptail_len(name);
>  	blen = __vfat_striptail_len(len, str);
> -	if (alen == blen) {
> -		if (nls_strnicmp(t, name->name, str, alen) == 0)
> -			return 0;
> -	}
> -	return 1;
> +	if (alen != blen)
> +		return 1;
> +	else if (utf8)
> +		return fat_utf8_strnicmp(name->name, str, alen);
> +	else
> +		return nls_strnicmp(t, name->name, str, alen);
>  }
>  
>  /*
> -- 
> 2.20.1
> 

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