linux-ext4 - Re: [PATCH 5/6] f2fs: switch to using fscrypt_match

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Date:   Tue, 25 Apr 2017 15:37:56 +0200
From:   Richard Weinberger <richard.weinberger@...il.com>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     linux-fscrypt@...r.kernel.org,
        Ryo Hashimoto <hashimoto@...omium.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>, linux-ext4@...r.kernel.org,
        Kazuhiro Inaba <kinaba@...omium.org>,
        David Gstir <david@...ma-star.at>
Subject: Re: [PATCH 5/6] f2fs: switch to using fscrypt_match_name()

Eric, Jaegeuk,


On Mon, Apr 24, 2017 at 7:00 PM, Eric Biggers <ebiggers3@...il.com> wrote:
> From: Eric Biggers <ebiggers@...gle.com>
>
> Switch f2fs directory searches to use the fscrypt_match_name() helper
> function.  There should be no functional change.

> -#ifdef CONFIG_F2FS_FS_ENCRYPTION
> -               if (unlikely(!name->name)) {
> -                       if (fname->usr_fname->name[0] == '_') {
> -                               if (de_name.len > 32 &&
> -                                       !memcmp(de_name.name + ((de_name.len - 17) & ~15),
> -                                               fname->crypto_buf.name + 8, 16))
> -                                       goto found;
> -                               goto not_match;
> -                       }
> -                       name->name = fname->crypto_buf.name;
> -                       name->len = fname->crypto_buf.len;
> -               }

Sorry if this is a stupid question, but why do you have to compare hashes _and_
the last few bytes of the bigname?
A lookup via bigname gives you two 32bits hash values, and there I'd assume that
this is sufficient for a collisions free lookup. Especially since an
resumed readdir()
with a 64bits cookie has to work too on your filesystem.

-- 
Thanks,
//richard