linux-kernel - Re: [PATCH v2] platform/x86/amd/pmf: Use memdup

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Message-Id: <1D5BDE66-ABB3-41D9-ACB0-FBAC207D55DC@toblux.com>
Date: Thu, 30 May 2024 16:15:51 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: markus.elfring@....de,
 Shyam-sundar.S-k@....com,
 hdegoede@...hat.com,
 ilpo.jarvinen@...ux.intel.com,
 kernel-janitors@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v2] platform/x86/amd/pmf: Use memdup_user()

Hi Dan,

On 27. May 2024, at 12:38, Dan Carpenter <dan.carpenter@...aro.org> wrote:
> Also this check isn't great:
> 
> if (dev->policy_sz < header->length + 512)
> 
> header->length is a u32 that comes from the user, so the addition can
> overflow.  I can't immediately see how to exploit this though since we
> don't seem to use header->length after this (by itself).

How about

	if (header->length > U32_MAX - 512 || dev->policy_sz < header->length + 512)
		return -EINVAL;

to prevent a possible overflow?

header->length is used in the next line

	dev->policy_sz = header->length + 512;

and if the addition overflows, we end up setting dev->policy_sz to an 
invalid value.

Thanks,
Thorsten