Current control messages are small enough to not be split into multiple buffers but we could run into such a situation in the future or a malicious guest could cause such a situation.
So handle the entire iov request for control messages. Also ensure the size of the control request is >= what we expect otherwise we risk accessing memory that we don't own. Signed-off-by: Amit Shah <amit.s...@redhat.com> CC: Avi Kivity <a...@redhat.com> Reported-by: Avi Kivity <a...@redhat.com> --- hw/virtio-serial-bus.c | 34 +++++++++++++++++++++++++++++++--- 1 files changed, 31 insertions(+), 3 deletions(-) diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c index bd1223e..3edfeca 100644 --- a/hw/virtio-serial-bus.c +++ b/hw/virtio-serial-bus.c @@ -216,7 +216,7 @@ static void mon_event(const char *device, const uint32_t port_id, } /* Guest wants to notify us of some event */ -static void handle_control_message(VirtIOSerial *vser, void *buf) +static void handle_control_message(VirtIOSerial *vser, void *buf, size_t len) { struct VirtIOSerialPort *port; struct virtio_console_control cpkt, *gcpkt; @@ -225,6 +225,11 @@ static void handle_control_message(VirtIOSerial *vser, void *buf) gcpkt = buf; + if (len < sizeof(cpkt)) { + /* The guest sent an invalid control packet */ + return; + } + cpkt.event = lduw_p(&gcpkt->event); cpkt.value = lduw_p(&gcpkt->value); @@ -321,12 +326,35 @@ static void control_out(VirtIODevice *vdev, VirtQueue *vq) { VirtQueueElement elem; VirtIOSerial *vser; + uint8_t *buf; + size_t len; vser = DO_UPCAST(VirtIOSerial, vdev, vdev); + len = 0; + buf = NULL; while (virtqueue_pop(vq, &elem)) { - handle_control_message(vser, elem.out_sg[0].iov_base); - virtqueue_push(vq, &elem, elem.out_sg[0].iov_len); + size_t cur_len, copied; + + cur_len = iov_size(elem.out_sg, elem.out_num); + /* + * Allocate a new buf only if we didn't have one previously or + * if the size of the buf differs + */ + if (cur_len != len) { + if (len) { + qemu_free(buf); + } + buf = qemu_malloc(cur_len); + len = cur_len; + } + copied = iov_to_buf(elem.out_sg, elem.out_num, buf, 0, len); + + handle_control_message(vser, buf, copied); + virtqueue_push(vq, &elem, copied); + } + if (len) { + qemu_free(buf); } virtio_notify(vdev, vq); } -- 1.6.2.5