linux-kernel - Re: [PATCH 6/7] btrfs: Promote to unsigned long long before shifting

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Date:   Mon, 26 Oct 2020 17:35:46 +0100
From:   David Sterba <dsterba@...e.cz>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, ericvh@...il.com, lucho@...kov.net,
        viro@...iv.linux.org.uk, jlayton@...nel.org, idryomov@...il.com,
        mark@...heh.com, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com,
        v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        ceph-devel@...r.kernel.org, ocfs2-devel@....oracle.com,
        linux-btrfs@...r.kernel.org, clm@...com, josef@...icpanda.com,
        dsterba@...e.com, stable@...r.kernel.org
Subject: Re: [PATCH 6/7] btrfs: Promote to unsigned long long before shifting

On Sun, Oct 04, 2020 at 07:04:27PM +0100, Matthew Wilcox (Oracle) wrote:
> On 32-bit systems, this shift will overflow for files larger than 4GB.
> 
> Cc: stable@...r.kernel.org
> Fixes: 53b381b3abeb ("Btrfs: RAID5 and RAID6")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  fs/btrfs/raid56.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
> index 255490f42b5d..5ee0a53301bd 100644
> --- a/fs/btrfs/raid56.c
> +++ b/fs/btrfs/raid56.c
> @@ -1089,7 +1089,7 @@ static int rbio_add_io_page(struct btrfs_raid_bio *rbio,
>  	u64 disk_start;
>  
>  	stripe = &rbio->bbio->stripes[stripe_nr];
> -	disk_start = stripe->physical + (page_index << PAGE_SHIFT);
> +	disk_start = stripe->physical + ((loff_t)page_index << PAGE_SHIFT);

It seems that this patch is mechanical replacement. If you check the
callers, the page_index is passed from an int that iterates over bits
set in an unsigned long (bitmap). The result won't overflow.