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

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Message-ID: <20201026170354.GR6756@twin.jikos.cz>
Date:   Mon, 26 Oct 2020 18:03:54 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dsterba@...e.cz, 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 Mon, Oct 26, 2020 at 04:44:42PM +0000, Matthew Wilcox wrote:
> On Mon, Oct 26, 2020 at 05:35:46PM +0100, David Sterba wrote:
> > 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.
> 
> Not mechanical, but I clearly made mistakes.  Will you pick up the
> patches which actually fix bugs?

Yes, I just replied to the first patch, that does fix an overflow.