Re: [PATCH 53/82] fs: Refactor intentional wrap-around test

[Jan Kara]

On Mon 22-01-24 16:27:28, 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: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Looks good atlhough I'd prefer wrapping the line to not overflow 80 chars.
Anyway feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/remap_range.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/remap_range.c b/fs/remap_range.c
> index f8c1120b8311..15e91bf2c5e3 100644
> --- a/fs/remap_range.c
> +++ b/fs/remap_range.c
> @@ -45,7 +45,7 @@ static int generic_remap_checks(struct file *file_in, loff_t pos_in,
>  		return -EINVAL;
>  
>  	/* Ensure offsets don't wrap. */
> -	if (pos_in + count < pos_in || pos_out + count < pos_out)
> +	if (add_would_overflow(pos_in, count) || add_would_overflow(pos_out, count))
>  		return -EINVAL;
>  
>  	size_in = i_size_read(inode_in);
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR