linux-ext4 - Re: [PATCH] ext4: Avoid creating new file in append-only dir when open(2) return error

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Message-ID: <CA+dCu8_bMXy3FN9BWFUwCcg4=peH93Mv7CcypShfQETA71Hebw@mail.gmail.com>
Date:	Sun, 30 Oct 2011 09:23:47 +0800
From:	Eryu Guan <guaneryu@...il.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Avoid creating new file in append-only dir when
 open(2) return error

On Sun, Oct 30, 2011 at 2:54 AM, Ted Ts'o <tytso@....edu> wrote:
> On Sat, Oct 29, 2011 at 02:02:41AM +0800, Eryu Guan wrote:
>> Newly created file on ext4 inherits inode flags from parent directory,
>> so new inode created in append-only directory has S_APPEND flag set,
>> may_open() called by do_last() checks that flag then returns -EPERM,
>> but at that time the new inode is already created.
>
> I have the following patch in the ext4 tree that should take care of
> this issue for ext2/3/4.
>
>                                                - Ted
>
> ext2,ext3,ext4: don't inherit APPEND_FL or IMMUTABLE_FL for new inodes
>
> This doesn't make much sense, and it exposes a bug in the kernel where
> attempts to create a new file in an append-only directory using
> O_CREAT will fail (but still leave a zero-length file).  This was
> discovered when xfstests #79 was generalized so it could run on all
> file systems.
>

I also found this by checking xfstests 079 and wanted to fix it in a way not
changing the current behavior. Masking out EXTN_APPEND_FL from inherit bits
makes more sense.

I think I should resend the comment cleanup part.

Thanks!

Eryu Guan
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