linux-kernel - RE: [RFC]PATCH] exfat: integrates dir-entry getting and validation

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Date:   Mon, 13 Jul 2020 11:19:29 +0900
From:   "Sungjong Seo" <sj1557.seo@...sung.com>
To:     "'Tetsuhiro Kohada'" <kohada.t2@...il.com>
Cc:     <kohada.tetsuhiro@...mitsubishielectric.co.jp>,
        <mori.takahiro@...mitsubishielectric.co.jp>,
        <motai.hirotaka@...mitsubishielectric.co.jp>,
        "'Namjae Jeon'" <namjae.jeon@...sung.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [RFC]PATCH] exfat: integrates dir-entry getting and validation

> Add validation for num, bh and type on getting dir-entry.
> ('file' and 'stream-ext' dir-entries are pre-validated to ensure success)
> Renamed exfat_get_dentry_cached() to exfat_get_validated_dentry() due to a
> change in functionality.
> 
> Integrate type-validation with simplified.
> This will also recognize a dir-entry set that contains 'benign secondary'
> dir-entries.
> 
> And, rename TYPE_EXTEND to TYPE_NAME.
> 
> Suggested-by: Sungjong Seo <sj1557.seo@...sung.com>
> Signed-off-by: Tetsuhiro Kohada <kohada.t2@...il.com>
> ---
>  fs/exfat/dir.c      | 144 ++++++++++++++++++--------------------------
>  fs/exfat/exfat_fs.h |  15 +++--
>  fs/exfat/file.c     |   4 +-
>  fs/exfat/inode.c    |   6 +-
>  fs/exfat/namei.c    |   4 +-
>  5 files changed, 73 insertions(+), 100 deletions(-)
> 
> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c index
> f4cea9a7fd02..e029e0986edc 100644
> --- a/fs/exfat/dir.c
> +++ b/fs/exfat/dir.c
[snip]
>   */
>  struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block
*sb,
> -		struct exfat_chain *p_dir, int entry, unsigned int type)
> +		struct exfat_chain *p_dir, int entry, int max_entries)
>  {
>  	int ret, i, num_bh;
> -	unsigned int off, byte_offset, clu = 0;
> +	unsigned int byte_offset, clu = 0;
>  	sector_t sec;
>  	struct exfat_sb_info *sbi = EXFAT_SB(sb);
>  	struct exfat_entry_set_cache *es;
>  	struct exfat_dentry *ep;
> -	int num_entries;
> -	enum exfat_validate_dentry_mode mode = ES_MODE_STARTED;
>  	struct buffer_head *bh;
> 
>  	if (p_dir->dir == DIR_DELETED) {
> @@ -844,13 +815,13 @@ struct exfat_entry_set_cache
> *exfat_get_dentry_set(struct super_block *sb,
>  		return NULL;
>  	es->sb = sb;
>  	es->modified = false;
> +	es->num_entries = 1;
> 
>  	/* byte offset in cluster */
>  	byte_offset = EXFAT_CLU_OFFSET(byte_offset, sbi);
> 
>  	/* byte offset in sector */
> -	off = EXFAT_BLK_OFFSET(byte_offset, sb);
> -	es->start_off = off;
> +	es->start_off = EXFAT_BLK_OFFSET(byte_offset, sb);
> 
>  	/* sector offset in cluster */
>  	sec = EXFAT_B_TO_BLK(byte_offset, sb); @@ -861,15 +832,12 @@ struct
> exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
>  		goto free_es;
>  	es->bh[es->num_bh++] = bh;
> 
> -	ep = exfat_get_dentry_cached(es, 0);
> -	if (!exfat_validate_entry(exfat_get_entry_type(ep), &mode))
> +	ep = exfat_get_validated_dentry(es, 0, TYPE_FILE);
> +	if (!ep)
>  		goto free_es;
> +	es->num_entries = min(ep->dentry.file.num_ext + 1, max_entries);
> 
> -	num_entries = type == ES_ALL_ENTRIES ?
> -		ep->dentry.file.num_ext + 1 : type;
> -	es->num_entries = num_entries;
> -
> -	num_bh = EXFAT_B_TO_BLK_ROUND_UP(off + num_entries * DENTRY_SIZE,
> sb);
> +	num_bh = EXFAT_B_TO_BLK_ROUND_UP(es->start_off  + es->num_entries *
> +DENTRY_SIZE, sb);
>  	for (i = 1; i < num_bh; i++) {
>  		/* get the next sector */
>  		if (exfat_is_last_sector_in_cluster(sbi, sec)) { @@ -889,11
> +857,13 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct
> super_block *sb,
>  	}
> 
>  	/* validiate cached dentries */
> -	for (i = 1; i < num_entries; i++) {
> -		ep = exfat_get_dentry_cached(es, i);
> -		if (!exfat_validate_entry(exfat_get_entry_type(ep), &mode))

> +	for (i = 1; i < es->num_entries; i++) {
> +		if (!exfat_get_validated_dentry(es, i, TYPE_SECONDARY))
>  			goto free_es;
>  	}
> +	if (!exfat_get_validated_dentry(es, 1, TYPE_STREAM))
> +		goto free_es;

It looks better to move checking TYPE_STREAM above the for-loop.
And then for-loop should start from index 2.

BTW, do you think it is enough to check only TYPE_SECONDARY not TYPE NAME?
As you might know, FILE, STREAM and NAME entries must be consecutive in
order.

> +
>  	return es;
>