linux-kernel - Re: [PATCH v2] vfat: don't read garbage after last dirent

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Date:   Mon, 24 Dec 2018 21:14:49 +0900
From:   OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:     Matteo Croce <mcroce@...hat.com>
Cc:     Timothy Redaelli <tredaelli@...hat.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] vfat: don't read garbage after last dirent

Matteo Croce <mcroce@...hat.com> writes:

> The FAT32 File System Specification[1] states that:
>
>     If DIR_Name[0] == 0x00, then the directory entry is free, and there
>     are no allocated directory entries after this one.
>
>     The special 0 value, indicates to FAT file system driver code that
>     the rest of the entries in this directory do not need to be examined
>     because they are all free.
>
> This is not enforced by Linux, and is possible to read garbage if not
> all dirents after the last one are filled with zeroes.
>
> [1] http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc
>
> Reported-by: Timothy Redaelli <tredaelli@...hat.com>
> Signed-off-by: Matteo Croce <mcroce@...hat.com>

We have to handle all paths that is using fat_get_entry(), to make
consistent behavior.

With quick check, there are still several issues remaining. Please check
more. For example, looks like fat_parse_long()/fat_search_long() path is
missing, and fat_get_dotdot_entry(), fat_subdirs() too.

(while adding new entry, if we found zeroed entry, we would be better to
warn about fsck.)

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>