Re: [PATCH] io_uring/rsrc: bound io_coalesce_buffer() page array allocation

[Gabriel Krisman Bertazi]

Yi Xie <xieyi@xxxxxxxxxx> writes:

> kvmalloc_objs() in io_coalesce_buffer() does not check for size overflow
> when nr_folios is large.  Mirror the check used in memmap.c before
> allocating the page pointer array.
>
> Signed-off-by: Yi Xie <xieyi@xxxxxxxxxx>

Resending from yesterday as changing MUA is never harmless...

I don't think this can happen.

nr_folios comes from nr_pages in io_check_coalesce_buffer, and must be
less or equal to it.  But nr_pages is already checked in io_pin_pages,
introduced by:

  https://lore.kernel.org/io-uring/178216289049.99876.2987989144128669864.b4-ty@b4/T/#t

> ---
>  io_uring/rsrc.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index 8d0f2ee24e0c..f1f8d6dd102c 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -776,6 +776,8 @@ static bool io_coalesce_buffer(struct page ***pages, int *nr_pages,
>  	unsigned i, j;
>  
>  	/* Store head pages only*/
> +	if (nr_folios > INT_MAX / sizeof(struct page *))
> +		return false;
>  	new_array = kvmalloc_objs(struct page *, nr_folios);
>  	if (!new_array)
>  		return false;
> -- 
> 2.25.1
>

-- 
Gabriel Krisman Bertazi