linux-kernel - Re: [syzbot] [virt?] upstream test error: KMSAN: use-after-free in vring_map_one

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Message-ID: <20251013040810-mutt-send-email-mst@kernel.org>
Date: Mon, 13 Oct 2025 04:08:41 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>,
	syzbot <syzbot+ac856b8b866cca41352c@...kaller.appspotmail.com>,
	eperezma@...hat.com, linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com, virtualization@...ts.linux.dev,
	xuanzhuo@...ux.alibaba.com
Subject: Re: [syzbot] [virt?] upstream test error: KMSAN: use-after-free in
 vring_map_one_sg

On Mon, Oct 13, 2025 at 09:37:29AM +0200, Paolo Abeni wrote:
> On 10/13/25 9:20 AM, Jason Wang wrote:
> > On Mon, Oct 13, 2025 at 1:29 PM Jason Wang <jasowang@...hat.com> wrote:
> >> On Sat, Oct 11, 2025 at 3:40 PM Jason Wang <jasowang@...hat.com> wrote:
> >>>
> >>> #syz test
> >>>
> >>> On Sat, Oct 11, 2025 at 4:38 AM syzbot
> >>> <syzbot+ac856b8b866cca41352c@...kaller.appspotmail.com> wrote:
> >>
> >> Paolo, it looks like the GSO tunnel features will leave uninitialized
> >> vnet header field which trigger KMSAN warning.
> >>
> >> Please have a look at the patch (which has been tested by syzbot) or
> >> propose another one.
> > 
> > Forget the attachment.
> 
> I have a few questions. The report mentions both UaF and uninit; the
> patch addresses "just" the uninit access. It's not clear to me if and
> how the UaF is addressed, and why/if it's related to the uninit access.


I'd like to understand that, too.

> Do you know better?
> 
> It looks like the uninit root cause is on "the other side"? i.e. the
> device not initializing properly the header. Would unconditionally
> clearing the hash info implicitly disable such feature?
> 
> The syzbot dashboard mentions a (no more available) reproducer. Do you
> have it cached somewhere?
> 
> Thanks,
> 
> Paolo