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virtio-9p: handle handle_9p_output() error 

A broken guest may send a request without providing buffers for the reply
or for the request itself, and virtqueue_pop() will return an element with
either in_num == 0 or out_num == 0.

All 9P requests are expected to start with the following 7-byte header:

            uint32_t size_le;
            uint8_t id;
            uint16_t tag_le;

If iov_to_buf() fails to return these 7 bytes, then something is wrong in
the guest.

In both cases, it is wrong to crash QEMU, since the root cause lies in the
guest.

This patch hence does the following:
- keep the check of in_num since pdu_complete() assumes it has enough
  space to store the reply and we will send something broken to the guest
- let iov_to_buf() handle out_num == 0, since it will return 0 just like
  if the guest had provided an zero-sized buffer.
- call virtio_error() to inform the guest that the device is now broken,
  instead of aborting
- detach the request from the virtqueue and free it

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Greg Kurz 2016-09-30 17:12:58 +02:00 committed by Michael S. Tsirkin
parent d14dde5ec7
commit d3d74d6fe0
1 changed files with 21 additions and 5 deletions
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26
hw/9pfs/virtio-9p-device.c
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@ -41,6 +41,7 @@ static void handle_9p_output(VirtIODevice *vdev, VirtQueue *vq)
V9fsState *s = &v->state;
V9fsPDU *pdu;
ssize_t len;
VirtQueueElement *elem;
while ((pdu = pdu_alloc(s))) {
struct {
@ -48,21 +49,28 @@ static void handle_9p_output(VirtIODevice *vdev, VirtQueue *vq)
uint8_t id;
uint16_t tag_le;
} QEMU_PACKED out;
VirtQueueElement *elem;
elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
if (!elem) {
pdu_free(pdu);
break;
goto out_free_pdu;
}
BUG_ON(elem->out_num == 0 || elem->in_num == 0);
if (elem->in_num == 0) {
virtio_error(vdev,
"The guest sent a VirtFS request without space for "
"the reply");
goto out_free_req;
}
QEMU_BUILD_BUG_ON(sizeof(out) != 7);
v->elems[pdu->idx] = elem;
len = iov_to_buf(elem->out_sg, elem->out_num, 0,
&out, sizeof(out));
BUG_ON(len != sizeof(out));
if (len != sizeof(out)) {
virtio_error(vdev, "The guest sent a malformed VirtFS request: "
"header size is %zd, should be 7", len);
goto out_free_req;
}
pdu->size = le32_to_cpu(out.size_le);
@ -72,6 +80,14 @@ static void handle_9p_output(VirtIODevice *vdev, VirtQueue *vq)
qemu_co_queue_init(&pdu->complete);
pdu_submit(pdu);
}
return;
out_free_req:
virtqueue_detach_element(vq, elem, 0);
g_free(elem);
out_free_pdu:
pdu_free(pdu);
}
static uint64_t virtio_9p_get_features(VirtIODevice *vdev, uint64_t features,