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[PATCH 2/2] btrfs: avoid overflowing f_bfree

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  [PATCH 2/2] btrfs: avoid overflowing f_bfree Luis de Bethencourt <luisbg@osg.samsung.com> - 2016-03-30 23:00 +0200
    Re: [PATCH 2/2] btrfs: avoid overflowing f_bfree Filipe Manana <fdmanana@gmail.com> - 2016-03-30 23:50 +0200
      Re: [PATCH 2/2] btrfs: avoid overflowing f_bfree Luis de Bethencourt <luisbg@osg.samsung.com> - 2016-03-31 00:20 +0200

#1367609 — [PATCH 2/2] btrfs: avoid overflowing f_bfree

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@osg.samsung.com>
Suggested-by: David Sterba <dsterba@suse.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;
+	/* 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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#1367626

On Wed, Mar 30, 2016 at 9:53 PM, Luis de Bethencourt
<luisbg@osg.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@osg.samsung.com>
> Suggested-by: David Sterba <dsterba@suse.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
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html



-- 
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."

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#1367648

On 30/03/16 22:48, Filipe Manana wrote:
> On Wed, Mar 30, 2016 at 9:53 PM, Luis de Bethencourt
> <luisbg@osg.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@osg.samsung.com>
>> Suggested-by: David Sterba <dsterba@suse.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
>>
>> --

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