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Re: [PATCH 0/1] uas: add stream number sanity checks (maybe 6.1)

From: Mauro Matteo Cascella
Subject: Re: [PATCH 0/1] uas: add stream number sanity checks (maybe 6.1)
Date: Mon, 23 Aug 2021 11:59:07 +0200


On Fri, Aug 20, 2021 at 3:07 PM Philippe Mathieu-Daudé
<philmd@redhat.com> wrote:
> Cc'ing Mauro to double-check.
> On 8/20/21 2:12 PM, Peter Maydell wrote:
> > On Wed, 18 Aug 2021 at 13:10, Gerd Hoffmann <kraxel@redhat.com> wrote:
> >>
> >> Security fix.  Sorry for the last-minute patch, I had completely
> >> forgotten this one until the CVE number for it arrived today.
> >>
> >> Given that the classic usb storage device is way more popular than
> >> the uas (usb attached scsi) device the impact should be pretty low
> >> and we might consider to not screw up our release schedule for this.
> >
> > What's the impact if the bug is exploited ?
> Bug class: "guest-triggered user-after-free".
> Being privileged (root) in the guest, you can leak some data from
> the host process then DoS the host or potentially exploit the
> use-after-free to execute code on the host.

This is actually an out-of-bounds access issue (not UAF). It's still
potentially bad, but I agree with Gerd the impact is low. Plus there's
an assert right before [1] that makes it a DoS if the accessed memory
is not NULL.

[1] https://gitlab.com/qemu-project/qemu/-/blob/master/hw/usb/dev-uas.c#L850

Mauro Matteo Cascella
Red Hat Product Security
PGP-Key ID: BB3410B0

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