linux-kernel - Re: [PATCH 2/3] scsi: megaraid_sas: check user-provided offsets

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Date:   Sat, 12 Sep 2020 08:20:53 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Kashyap Desai <kashyap.desai@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        hch@...radead.org, stable@...r.kernel.org,
        Anand Lodnoor <anand.lodnoor@...adcom.com>,
        Chandrakanth Patil <chandrakanth.patil@...adcom.com>,
        Hannes Reinecke <hare@...e.de>, megaraidlinux.pdl@...adcom.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] scsi: megaraid_sas: check user-provided offsets

On Tue, Sep 08, 2020 at 11:36:22PM +0200, Arnd Bergmann wrote:
> It sounds unwise to let user space pass an unchecked 32-bit
> offset into a kernel structure in an ioctl. This is an unsigned
> variable, so checking the upper bound for the size of the structure
> it points into is sufficient to avoid data corruption, but as
> the pointer might also be unaligned, it has to be written carefully
> as well.
> 
> While I stumbled over this problem by reading the code, I did not
> continue checking the function for further problems like it.

Oh, yikes!

> 
> Cc: stable@...r.kernel.org

What about a Fixes tag instead?

>  	if (ioc->sense_len) {
> +		/* make sure the pointer is part of the frame */
> +		if (ioc->sense_off > (sizeof(union megasas_frame) - sizeof(__le64))) {

No need for the inner braces and please avoid over 80 char lines.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@....de>