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

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Date:	Wed, 30 Mar 2016 23:10:16 +0100
From:	Luis de Bethencourt <luisbg@....samsung.com>
To:	fdmanana@...il.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 30/03/16 22:48, Filipe Manana wrote:
> 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?
> 

Shoot! Indeed I did, sorry. Thanks for noticing.

Sending version 2.

Luis

>> +       /* 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
>>
>> --