linux-hardening - Re: [PATCH] md/raid5: Convert stripe_head's "dev" to flexible array member

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Date:   Wed, 17 May 2023 21:27:24 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Song Liu <song@...nel.org>, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] md/raid5: Convert stripe_head's "dev" to flexible array
 member

On Wed, May 17, 2023 at 04:33:14PM -0700, Kees Cook wrote:
>  	sc = kmem_cache_create(conf->cache_name[conf->active_name],
> -			       sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
> +			       struct_size((struct stripe_head *)0, dev, devs),
>  			       0, 0, NULL);
>  	if (!sc)
>  		return 1;
> @@ -2559,7 +2559,7 @@ static int resize_stripes(struct r5conf *conf, int newsize)
>  
>  	/* Step 1 */
>  	sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
> -			       sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
> +			       struct_size((struct stripe_head *)0, dev, newsize),

The constant you're casting here should be NULL, not 0.
Also given that this expression is duplicated, I'd suggest a little
helper for it…

> -	} dev[1]; /* allocated with extra space depending of RAID geometry */
> +	} dev[]; /* allocated with extra space depending of RAID geometry */

And this isn't extra space over the single entry anymore, so I'd
change this to:

	/* allocated depending of RAID geometry */