Re: [PATCH] md/raid10: fix divide-by-zero in setup_geo() with zero far_copies

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Junrui,


Thank you for the patch.

Am 16.04.26 um 05:39 schrieb Junrui Luo:
> setup_geo() extracts near_copies (nc) and far_copies (fc) from the
> user-provided layout parameter without checking for zero. When fc=0
> with the "improved" far set layout selected, 'geo->far_set_size =
> disks / fc' triggers a divide-by-zero.
> 
> Validate nc and fc immediately after extraction, returning -1 if
> either is zero.

Why also `nc` and not just `fc`?

It’d be great, if you documented the command how to create such a layout.

> Fixes: 475901aff158 ("MD RAID10: Improve redundancy for 'far' and 'offset' algorithms (part 1)")
> Reported-by: Yuhao Jiang <danisjiang@gmail.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
> ---
>   drivers/md/raid10.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 0653b5d8545a..811ea3d23b80 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -3791,6 +3791,8 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
>   	nc = layout & 255;
>   	fc = (layout >> 8) & 255;
>   	fo = layout & (1<<16);
> +	if (!nc || !fc)
> +		return -1;

I’d also print a warning, so the user knows, what was wrong:

     pr_warn(md/raid10:%s: near and far copies need to be greater than 
0, mdname(mddev));

>   	geo->raid_disks = disks;
>   	geo->near_copies = nc;
>   	geo->far_copies = fc;


Kind regards,

Paul