Re: [PATCH 3/3] btrfs: Avoid possible qgroup_rsv_size overflow in btrfs_calculate_inode_block_rsv_size

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2019/3/18 下午11:45, Nikolay Borisov wrote:
> qgroup_rsv_size is calculated as the product of
> outstanding_extent * fs_info->nodesize. The product is calculated with
> 32 bith precision since both variables are defined as u32. Yet
> qgroup_rsv_size expects a 64 bit result.
> 
> Avoid possible multiplication overflow by casting outstanding_extent to
> u64.
> 
> Fixes-coverity-id: 1435101
> ff6bc37eb7f6 ("btrfs: qgroup: Use independent and accurate per inode qgroup rsv")
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/extent-tree.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index b085d8215f0e..beddf9eef4a2 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -6173,7 +6173,7 @@ static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info,
>  	 *
>  	 * This is overestimating in most cases.
>  	 */
> -	qgroup_rsv_size = outstanding_extents * fs_info->nodesize;
> +	qgroup_rsv_size = (u64) outstanding_extents * fs_info->nodesize;

I'm a little uncertain about what's the proper way to do a u32 * u32 and
get a u64 in C.

For division we have DIV macro but not for multiple.

Thanks,
Qu

>  
>  	spin_lock(&block_rsv->lock);
>  	block_rsv->size = reserve_size;
>