On Mon, Apr 22, 2024 at 09:00:31AM -0400, Stefan Hajnoczi wrote:
> 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@xxxxxxxxxx>
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!
commit bcc17a060d93b198d8a17a9b87b593f41337ee28
Author: Michael S. Tsirkin <mst@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Jeongjun Park <aha310510@xxxxxxxxx>
Fixes: ced7b713711f ("vhost/vsock: support SEQPACKET for transport").
Cc: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
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];
