linux-kernel - RE: [PATCH] ACPI: scan: Fix a Hyper-V Linux VM panic caused by buffer overflow

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Date:   Fri, 8 Jan 2021 07:06:53 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     Michael Kelley <mikelley@...rosoft.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "len.brown@...el.com" <len.brown@...el.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>
Subject: RE: [PATCH] ACPI: scan: Fix a Hyper-V Linux VM panic caused by buffer
 overflow

> From: Rafael J. Wysocki <rafael@...nel.org>
> Sent: Thursday, January 7, 2021 5:48 AM
> > > > Linux VM on Hyper-V crashes with the latest mainline:
> > > > ...
> The root cause is a VM issue AFAICS, though.

Yes.
 
> It doesn't look like the right fix to me, though.
> 
> The problem appears to be that the string coming from _HID is too long
> (which is a spec violation). 

Yes. We have requested Hyper-V team to fix the buggy BIOS/firmware,
but we have to cope with the existing buggy Hyper-V hosts, at least
before the Hyper-V fix is deployed to the hosts, and some old versions
of the hosts may not get updated. :-(

> The patch truncates it to match the
> length of the target buffer, but that is not particularly useful.
> 
> It would be better to use something like kstrdup_const() to initialize
> acpi_device_bus_id->bus_id IMV.

Makes sense. I'll submit v2 shortly.

Thanks,
-- Dexuan