linux-ext4 - Re: [PATCH 3/3] e4defrag: avoid unsuccessful return in non-privileged user

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Message-ID: <87f94c370909301137s40f09b7wb08ca7dee9f8dd15@mail.gmail.com>
Date:	Wed, 30 Sep 2009 14:37:24 -0400
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Kazuya Mio <k-mio@...jp.nec.com>
Cc:	linux-ext4@...r.kernel.org, Theodore Tso <tytso@....edu>
Subject: Re: [PATCH 3/3] e4defrag: avoid unsuccessful return in non-privileged 
	user

2009/9/30 Kazuya Mio <k-mio@...jp.nec.com>:
> If non-privileged user does e4defrag, e4defrag returns 1 despite
> its success. This patch fixes this problem.
>
> Signed-off-by: Kazuya Mio <k-mio@...jp.nec.com>
> ---
>
>  e4defrag.c |    1 +
>  1 file changed, 1 insertion(+)
> diff --git a/misc/e4defrag.c b/misc/e4defrag.c
> index 94f8529..98dda92 100644
> --- a/misc/e4defrag.c
> +++ b/misc/e4defrag.c
> @@ -2025,6 +2025,7 @@ int main(int argc, char *argv[])
>                                if (!(mode_flag & DETAIL) &&
>                                                current_uid != ROOT_UID) {
>                                        printf(" Done.\n");
> +                                       success_flag = 1;
>                                        continue;
>                                }

I should know this, but this patch made me wonder about the underlying
implementation of EXT4_IOC_MOVE_EXT.

After EXT4_IOC_MOVE_EXT is called, can userspace somehow modify the
defragged file?

ie. If I only have readonly access to a file and I call
EXT4_IOC_MOVE_EXT to replace some of the data blocks, is it possible
now for me to write data to the donor_fd and thus modify the data in
the original file?

Greg
-- 
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