Re: [PATCH 37/82] aio: Refactor intentional wrap-around test

[Jan Kara]

On Mon 22-01-24 16:27:12, Kees Cook wrote:
> In an effort to separate intentional arithmetic wrap-around from
> unexpected wrap-around, we need to refactor places that depend on this
> kind of math. One of the most common code patterns of this is:
> 
> 	VAR + value < VAR
> 
> Notably, this is considered "undefined behavior" for signed and pointer
> types, which the kernel works around by using the -fno-strict-overflow
> option in the build[1] (which used to just be -fwrapv). Regardless, we
> want to get the kernel source to the position where we can meaningfully
> instrument arithmetic wrap-around conditions and catch them when they
> are unexpected, regardless of whether they are signed[2], unsigned[3],
> or pointer[4] types.
> 
> Refactor open-coded wrap-around addition test to use add_would_overflow().
> This paves the way to enabling the wrap-around sanitizers in the future.
> 
> Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
> Link: https://github.com/KSPP/linux/issues/26 [2]
> Link: https://github.com/KSPP/linux/issues/27 [3]
> Link: https://github.com/KSPP/linux/issues/344 [4]
> Cc: Benjamin LaHaise <bcrl@xxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: linux-aio@xxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/aio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index bb2ff48991f3..edd19be3f4b1 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -796,7 +796,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
>  	/* limit the number of system wide aios */
>  	spin_lock(&aio_nr_lock);
>  	if (aio_nr + ctx->max_reqs > aio_max_nr ||
> -	    aio_nr + ctx->max_reqs < aio_nr) {
> +	    add_would_overflow(aio_nr, ctx->max_reqs)) {
>  		spin_unlock(&aio_nr_lock);
>  		err = -EAGAIN;
>  		goto err_ctx;
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR