linux-kernel - Re: [PATCH 1/2] staging: unisys: visorbus: address theoretical int overflows

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Message-ID: <20171128141148.3pkz6pwteuzoo2aa@mwanda>
Date:   Tue, 28 Nov 2017 17:11:49 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     David Kershner <david.kershner@...sys.com>
Cc:     gregkh@...uxfoundation.org, jes.sorensen@...il.com,
        linux-kernel@...r.kernel.org,
        driverdev-devel@...uxdriverproject.org, sparmaintainer@...sys.com,
        erik.arfvidson@...il.com, wadgaonkarsam@...il.com,
        Tim Sell <Timothy.Sell@...sys.com>
Subject: Re: [PATCH 1/2] staging: unisys: visorbus: address theoretical int
 overflows

> --- a/drivers/staging/unisys/visorbus/visorchipset.c
> +++ b/drivers/staging/unisys/visorbus/visorchipset.c
> @@ -581,7 +581,8 @@ static void *parser_name_get(struct parser_context *ctx)
>  	struct visor_controlvm_parameters_header *phdr;
>  
>  	phdr = &ctx->data;
> -	if (phdr->name_offset + phdr->name_length > ctx->param_bytes)
> +	if ((unsigned long)phdr->name_offset +
> +	    (unsigned long)phdr->name_length > ctx->param_bytes)
>  		return NULL;
>  	ctx->curr = (char *)&phdr + phdr->name_offset;
>  	ctx->bytes_remaining = phdr->name_length;


I haven't reviewed this code very thouroughly.  This should fix the
issue on 64 bit systems, but it's a no-op on 32 bit systems.  Which
might be fine?  I would be more comfortable if we just checked for
integer overflow explicitly.  There are bunch of ways to do that:

	if (phdr->name_offset > ctx->param_bytes ||
	    phdr->name_length > ctx->param_bytes ||
	    phdr->name_offset + phdr->name_length > ctx->param_bytes)

Or:

	if (phdr->name_offset + phdr->name_length < phdr->name_offset ||
	    phdr->name_offset + phdr->name_length > ctx->param_bytes)
		return NULL;

regards,
dan carpenter