linux-kernel - Re: [PATCH 1/7] 9P: Cast to loff

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Date:   Wed, 7 Oct 2020 06:48:49 +0100
From:   Christoph Hellwig <hch@...radead.org>
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 1/7] 9P: Cast to loff_t before multiplying

On Sun, Oct 04, 2020 at 07:04:22PM +0100, Matthew Wilcox (Oracle) wrote:
> On 32-bit systems, this multiplication will overflow for files larger
> than 4GB.
> 
> Cc: stable@...r.kernel.org
> Fixes: fb89b45cdfdc ("9P: introduction of a new cache=mmap model.")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  fs/9p/vfs_file.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
> index 3576123d8299..6d97b6b4d34b 100644
> --- a/fs/9p/vfs_file.c
> +++ b/fs/9p/vfs_file.c
> @@ -612,9 +612,9 @@ static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
>  	struct writeback_control wbc = {
>  		.nr_to_write = LONG_MAX,
>  		.sync_mode = WB_SYNC_ALL,
> -		.range_start = vma->vm_pgoff * PAGE_SIZE,
> +		.range_start = (loff_t)vma->vm_pgoff * PAGE_SIZE,

Given the may places where this issue shows up I think we really need
a vma_offset or similar helper for it.  Much better than chasing missing
casts everywhere.