linux-kernel - RE: [PATCH 1/2] exfat: add NameLength check when extracting name

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Date:   Thu, 13 Aug 2020 11:53:06 +0900
From:   "Namjae Jeon" <namjae.jeon@...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>,
        "'Sungjong Seo'" <sj1557.seo@...sung.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] exfat: add NameLength check when extracting name

> Thank you for your reply.
> 
> >> -static void exfat_get_uniname_from_ext_entry(struct super_block *sb,
> >> -		struct exfat_chain *p_dir, int entry, unsigned short *uniname)
> >> +static int exfat_get_uniname_from_name_entries(struct exfat_entry_set_cache *es,
> >> +		struct exfat_uni_name *uniname)
> >>   {
> >> -	int i;
> >> -	struct exfat_entry_set_cache *es;
> >> +	int n, l, i;
> >>   	struct exfat_dentry *ep;
> >>
> >> -	es = exfat_get_dentry_set(sb, p_dir, entry, ES_ALL_ENTRIES);
> >> -	if (!es)
> >> -		return;
> >> +	uniname->name_len = es->de_stream->name_len;
> >> +	if (uniname->name_len == 0)
> >> +		return -EIO;
> > Can we validate ->name_len and name entry ->type in exfat_get_dentry_set() ?
> 
> Yes.
> As I wrote in a previous email, entry type validation, name-length validation, and name extraction
> should not be separated, so implement all of these in exfat_get_dentry_set().
> It can be easily implemented by adding uniname to exfat_entry_set_cache and calling
> exfat_get_uniname_from_name_entries() from exfat_get_dentry_set().
No, We can check stream->name_len and name entry type in exfat_get_dentry_set().
And you are already checking entry type with TYPE_SECONDARY in
exfat_get_dentry_set(). Why do we have to check twice?

>
> However, that would be over-implementation.
> Not all callers of exfat_get_dentry_set() need a name.
Where? It will not checked with ES_2_ENTRIES.

> It is enough to validate the name when it is needed.
> This is a file-system driver, not fsck.
Sorry, I don't understand what you are talking about. If there is a problem
in ondisk-metadata, Filesystem should return error.

> Validation is possible in exfat_get_dentry_set(), but unnecessary.
> 
> Why do you want to validate the name in exfat_get_dentry_set()?
exfat_get_dentry_set validates file, stream entry. And you are trying to check
name entries with type_secondary. In addition, trying add the checksum check.
Conversely, Why would you want to add those checks to exfat_get_dentry_set()?
Why do we check only name entries separately? Aren't you intent to return
validated entry set in exfat_get_dentry_set()?
> 
> 
> BR
> ---
> Tetsuhiro Kohada <kohada.t2@...il.com>