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

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Date: Sun, 5 May 2024 22:53:39 +0300
From: Arseniy Krasnov <avkrasnov@...utedevices.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella
	<sgarzare@...hat.com>, Jeongjun Park <aha310510@...il.com>, Jason Wang
	<jasowang@...hat.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, LKML
	<linux-kernel@...r.kernel.org>, <virtualization@...ts.linux.dev>,
	<syzbot+6c21aeb59d0e82eb2782@...kaller.appspotmail.com>,
	<syzkaller-bugs@...glegroups.com>, Krasnov Arseniy <oxffffaa@...il.com>
Subject: Re: [PATCH virt] virt: fix uninit-value in vhost_vsock_dev_open

> But now that it's explained, the bugfix as proposed is incomplete:
> userspace can set features twice and the second time will leak
> old VIRTIO_VSOCK_F_SEQPACKET bit value.
> 
> And I am pretty sure the Fixes tag is wrong.
> 
> So I wrote this, but I actually don't have a set for
> seqpacket to test this. Arseny could you help test maybe?
> Thanks!

Hi! Sorry for late reply! Just run vsock test suite with this patch -
seems everything is ok!

> 
> 
> commit bcc17a060d93b198d8a17a9b87b593f41337ee28
> Author: Michael S. Tsirkin <mst@...hat.com>
> Date:   Mon Apr 22 10:03:13 2024 -0400
> 
> vhost/vsock: always initialize seqpacket_allow
> 
> There are two issues around seqpacket_allow:
> 1. seqpacket_allow is not initialized when socket is
> created. Thus if features are never set, it will be
> read uninitialized.
> 2. if VIRTIO_VSOCK_F_SEQPACKET is set and then cleared,
> then seqpacket_allow will not be cleared appropriately
> (existing apps I know about don't usually do this but
> it's legal and there's no way to be sure no one relies
> on this).
> 
> To fix:
>     - initialize seqpacket_allow after allocation
>     - set it unconditionally in set_features
> 
> Reported-by: syzbot+6c21aeb59d0e82eb2782@...kaller.appspotmail.com
> Reported-by: Jeongjun Park <aha310510@...il.com>
> Fixes: ced7b713711f ("vhost/vsock: support SEQPACKET for transport").
> Cc: Arseny Krasnov <arseny.krasnov@...persky.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Stefan Hajnoczi <stefanha@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

Acked-by: Arseniy Krasnov <avkrasnov@...utedevices.com>

> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index ec20ecff85c7..bf664ec9341b 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -667,6 +667,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>  	}
>  
>  	vsock->guest_cid = 0; /* no CID assigned yet */
> +	vsock->seqpacket_allow = false;
>  
>  	atomic_set(&vsock->queued_replies, 0);
>  
> @@ -810,8 +811,7 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
>  			goto err;
>  	}
>  
> -	if (features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET))
> -		vsock->seqpacket_allow = true;
> +	vsock->seqpacket_allow = features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET);
>  
>  	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
>  		vq = &vsock->vqs[i];