linux-kernel - Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev

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Date: Mon, 22 Apr 2024 09:00:31 -0400
From: Stefan Hajnoczi <stefanha@...hat.com>
To: Jeongjun Park <aha310510@...il.com>
Cc: mst@...hat.com, jasowang@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, sgarzare@...hat.com,
	syzbot+6c21aeb59d0e82eb2782@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com, virtualization@...ts.linux.dev,
	Arseny Krasnov <arseny.krasnov@...persky.com>
Subject: Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

On Sun, Apr 21, 2024 at 12:06:06PM +0900, Jeongjun Park wrote:
> static bool vhost_transport_seqpacket_allow(u32 remote_cid)
> {
> ....
> 	vsock = vhost_vsock_get(remote_cid);
> 
> 	if (vsock)
> 		seqpacket_allow = vsock->seqpacket_allow;
> ....
> }
> 
> I think this is due to reading a previously created uninitialized 
> vsock->seqpacket_allow inside vhost_transport_seqpacket_allow(), 
> which is executed by the function pointer present in the if statement.

CCing Arseny, author of commit ced7b713711f ("vhost/vsock: support
SEQPACKET for transport").

Looks like a genuine bug in the commit. vhost_vsock_set_features() sets
seqpacket_allow to true when the feature is negotiated. The assumption
is that the field defaults to false.

The rest of the vhost_vsock.ko code is written to initialize the
vhost_vsock fields, so you could argue seqpacket_allow should just be
explicitly initialized to false.

However, eliminating this class of errors by zeroing seems reasonable in
this code path. vhost_vsock_dev_open() is not performance-critical.

Acked-by: Stefan Hajnoczi <stefanha@...hat.com>

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