Re: [PATCH] iomap: Fix overflow in iomap_page_mkwrite

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Nov 06, 2019 at 08:04:00PM +0100, Andreas Gruenbacher wrote:
> On architectures where ssize_t is wider than pgoff_t, the expression

ssize_t?  But you're changing @offset, which is loff_t.   I'm confused.

Also, which architectures are you talking about here?

--D

> ((page->index + 1) << PAGE_SHIFT) can overflow.  Rewrite to use the page
> offset, which we already compute here anyway.
> 
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> ---
>  fs/iomap/buffered-io.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index e25901ae3ff4..a30ea7ecb790 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1040,20 +1040,19 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
>  
>  	lock_page(page);
>  	size = i_size_read(inode);
> -	if ((page->mapping != inode->i_mapping) ||
> -	    (page_offset(page) > size)) {
> +	offset = page_offset(page);
> +	if (page->mapping != inode->i_mapping || offset > size) {
>  		/* We overload EFAULT to mean page got truncated */
>  		ret = -EFAULT;
>  		goto out_unlock;
>  	}
>  
>  	/* page is wholly or partially inside EOF */
> -	if (((page->index + 1) << PAGE_SHIFT) > size)
> +	if (offset > size - PAGE_SIZE)
>  		length = offset_in_page(size);
>  	else
>  		length = PAGE_SIZE;
>  
> -	offset = page_offset(page);
>  	while (length > 0) {
>  		ret = iomap_apply(inode, offset, length,
>  				IOMAP_WRITE | IOMAP_FAULT, ops, page,
> -- 
> 2.20.1
>