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

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Date:   Sun, 3 Jan 2021 19:49:39 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     "James E.J. Bottomley" <jejb@...ux.ibm.com>
Cc:     Phil Oester <kernel@...uxace.com>, Arnd Bergmann <arnd@...db.de>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        "# 3.4.x" <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 <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] scsi: megaraid_sas: check user-provided offsets

On Sun, Jan 3, 2021 at 6:00 PM James Bottomley <jejb@...ux.ibm.com> wrote:
> On Sun, 2021-01-03 at 17:26 +0100, Arnd Bergmann wrote:
> [...]
> > @@ -8209,7 +8208,7 @@ megasas_mgmt_fw_ioctl(struct megasas_instance
> > *instance,
> >                 if (instance->consistent_mask_64bit)
> >                         put_unaligned_le64(sense_handle, sense_ptr);
> >                 else
> > -                       put_unaligned_le32(sense_handle, sense_ptr);
> > +                       put_unaligned_le64(sense_handle, sense_ptr);
> >         }
>
> This hunk can't be right.  It effectively means removing the if.

I'm just trying to restore the state before the regression introduced
in my 381d34e376e3 ("scsi: megaraid_sas: Check user-provided offsets").

The old code always stored 'sizeof(long)' bytes into sense_ptr,
regardless of instance->consistent_mask_64bit, but it would truncate
the address to 32 bit if that was cleared. This was clearly bogus
and I tried to make it do something more meaningful, only storing
8 bytes into the structure if it was configured for 64-bit DMA, regardless
of the capabilities of the kernel.

> However, the if is needed because sense_handle is a dma_addr_t which
> can be either 32 or 64 bit.  What about changing the if to
>
> if (sizeof(dma_addr_t) == 8)
>
> instead?

That would not be useful either, the device surely does not care
if the kernel supports 64-bit DMA. What we'd really need here is
someone with access to the interface specifications to see how
many bytes should be stored in the structure. I suspect always
storing 64 bits (as my patch does) is correct, and would send a
proper patch to remove the if() if Phil confirms that my test
patch fixes the regression.

        Arnd