| Message ID | 147487885500.6679.17365810852820160326.stgit@bahia |
|---|---|
| State | New |
| Headers | show |
On Mon, Sep 26, 2016 at 10:34:15AM +0200, Greg Kurz wrote: > 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> > --- > v3: - dropped the out_num check (already covered by iov_to_buf()) > - reworded the in_num error message > - added an error path to detach and free the virtqueue element > > I haven't added the R-b tags received during v2 because of the above > changes. > --- > hw/9pfs/virtio-9p-device.c | 26 +++++++++++++++++++++----- > 1 file changed, 21 insertions(+), 5 deletions(-) Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c index e7ea0e45f3dd..a338f6400264 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,
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> --- v3: - dropped the out_num check (already covered by iov_to_buf()) - reworded the in_num error message - added an error path to detach and free the virtqueue element I haven't added the R-b tags received during v2 because of the above changes. --- hw/9pfs/virtio-9p-device.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)