Re: [PATCH 1/7] 9P: Cast to loff_t before multiplying

From: Christoph Hellwig <hch@infradead.org>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, ericvh@gmail.com,
	lucho@ionkov.net, viro@zeniv.linux.org.uk, jlayton@kernel.org,
	idryomov@gmail.com, mark@fasheh.com, jlbec@evilplan.org,
	joseph.qi@linux.alibaba.com,
	v9fs-developer@lists.sourceforge.net,
	linux-kernel@vger.kernel.org, ceph-devel@vger.kernel.org,
	ocfs2-devel@oss.oracle.com, linux-btrfs@vger.kernel.org,
	clm@fb.com, josef@toxicpanda.com, dsterba@suse.com,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/7] 9P: Cast to loff_t before multiplying
Date: Wed, 7 Oct 2020 06:48:49 +0100	[thread overview]
Message-ID: <20201007054849.GA16556@infradead.org> (raw)
In-Reply-To: <20201004180428.14494-2-willy@infradead.org>

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@vger.kernel.org
> Fixes: fb89b45cdfdc ("9P: introduction of a new cache=mmap model.")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.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.