[RFC PATCH] vhost_vdpa: assign irq bypass producer token correctly

[Jason Wang <jasowang@redhat.com>]

We used to call irq_bypass_unregister_producer() in
vhost_vdpa_setup_vq_irq() which is problematic as we don't know if the
token pointer is still valid or not.

Actually, we use the eventfd_ctx as the token so the life cycle of the
token should be bound to the VHOST_SET_VRING_CALL instead of
vhost_vdpa_setup_vq_irq() which could be called by set_status().

Fixing this by setting up  irq bypass producer's token when handling
VHOST_SET_VRING_CALL and un-registering the producer before calling
vhost_vring_ioctl() to prevent a possible use after free as eventfd
could have been released in vhost_vring_ioctl().

Fixes: 2cf1ba9a4d15 ("vhost_vdpa: implement IRQ offloading in vhost_vdpa")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Note for Dragos: Please check whether this fixes your issue. I
slightly test it with vp_vdpa in L2.
---
 drivers/vhost/vdpa.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index e31ec9ebc4ce..388226a48bcc 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -209,11 +209,9 @@ static void vhost_vdpa_setup_vq_irq(struct vhost_vdpa *v, u16 qid)
 	if (irq < 0)
 		return;
 
-	irq_bypass_unregister_producer(&vq->call_ctx.producer);
 	if (!vq->call_ctx.ctx)
 		return;
 
-	vq->call_ctx.producer.token = vq->call_ctx.ctx;
 	vq->call_ctx.producer.irq = irq;
 	ret = irq_bypass_register_producer(&vq->call_ctx.producer);
 	if (unlikely(ret))
@@ -709,6 +707,12 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 			vq->last_avail_idx = vq_state.split.avail_index;
 		}
 		break;
+	case VHOST_SET_VRING_CALL:
+		if (vq->call_ctx.ctx) {
+			vhost_vdpa_unsetup_vq_irq(v, idx);
+			vq->call_ctx.producer.token = NULL;
+		}
+		break;
 	}
 
 	r = vhost_vring_ioctl(&v->vdev, cmd, argp);
@@ -747,13 +751,14 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 			cb.callback = vhost_vdpa_virtqueue_cb;
 			cb.private = vq;
 			cb.trigger = vq->call_ctx.ctx;
+			vq->call_ctx.producer.token = vq->call_ctx.ctx;
+			vhost_vdpa_setup_vq_irq(v, idx);
 		} else {
 			cb.callback = NULL;
 			cb.private = NULL;
 			cb.trigger = NULL;
 		}
 		ops->set_vq_cb(vdpa, idx, &cb);
-		vhost_vdpa_setup_vq_irq(v, idx);
 		break;
 
 	case VHOST_SET_VRING_NUM:
@@ -1419,6 +1424,7 @@ static int vhost_vdpa_open(struct inode *inode, struct file *filep)
 	for (i = 0; i < nvqs; i++) {
 		vqs[i] = &v->vqs[i];
 		vqs[i]->handle_kick = handle_vq_kick;
+		vqs[i]->call_ctx.ctx = NULL;
 	}
 	vhost_dev_init(dev, vqs, nvqs, 0, 0, 0, false,
 		       vhost_vdpa_process_iotlb_msg);
-- 
2.31.1