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@syzkaller.appspotmail.com
Reported-by: Jeongjun Park <redacted>
Fixes: ced7b713711f ("vhost/vsock: support SEQPACKET for transport").
Cc: Arseny Krasnov <redacted>
Cc: David S. Miller <davem@davemloft.net>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Arseniy Krasnov <redacted>
Tested-by: Arseniy Krasnov <redacted>

---


Reposting now it's been tested.

 drivers/vhost/vsock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

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];

-- 
MST