linux-kernel - Re: [PATCH 2/2] btrfs: avoid overflowing f

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Message-ID: <CAL3q7H7fFg0UNL_hR=rUpbGmFpM2QHK+ME4_NMn3zB4vuJYMcA@mail.gmail.com>
Date:	Wed, 30 Mar 2016 22:48:26 +0100
From:	Filipe Manana <fdmanana@...il.com>
To:	Luis de Bethencourt <luisbg@....samsung.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	David Sterba <dsterba@...e.com>,
	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH 2/2] btrfs: avoid overflowing f_bfree

On Wed, Mar 30, 2016 at 9:53 PM, Luis de Bethencourt
<luisbg@....samsung.com> wrote:
> Since mixed block groups accounting isn't byte-accurate and f_bree is an
> unsigned integer, it could overflow. Avoid this.
>
> Signed-off-by: Luis de Bethencourt <luisbg@....samsung.com>
> Suggested-by: David Sterba <dsterba@...e.com>
> ---
>  fs/btrfs/super.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index bdca79c..93376d0 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2101,6 +2101,11 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>         /* Account global block reserve as used, it's in logical size already */
>         spin_lock(&block_rsv->lock);
>         buf->f_bfree -= block_rsv->size >> bits;

You forgot to remove the line above, didn't you?

> +       /* Mixed block groups accounting is not byte-accurate, avoid overflow */
> +       if (buf->f_bfree >= block_rsv->size >> bits)
> +               buf->f_bfree -= block_rsv->size >> bits;
> +       else
> +               buf->f_bfree = 0;
>         spin_unlock(&block_rsv->lock);
>
>         buf->f_bavail = div_u64(total_free_data, factor);
> --
> 2.5.3
>
> --
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-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."