From: Greg Kurz <gr...@kaod.org>
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 <gr...@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
Reviewed-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
hw/9pfs/virtio-9p-device.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
index e7ea0e4..a338f64 100644
--- a/hw/9pfs/virtio-9p-device.c
+++ b/hw/9pfs/virtio-9p-device.c
@@ -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,
--
MST
