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virtio-balloon: fix a use-after-free case 

The elem could theorically contain both outbuf and inbufs. We move the
free operation to the end of this function to avoid using elem->in_sg
while elem has been freed.

Fixes: c13c4153f7
("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
CC: Michael S. Tsirkin <mst@redhat.com>
CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Peter Xu <peterx@redhat.com>
Message-Id: <1552383280-4122-1-git-send-email-wei.w.wang@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Wei Wang 2019-03-12 17:34:40 +08:00 committed by Michael S. Tsirkin
parent 9d86712365
commit ae440bd14c
1 changed files with 7 additions and 6 deletions
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13
hw/virtio/virtio-balloon.c
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@ -391,6 +391,7 @@ static bool get_free_page_hints(VirtIOBalloon *dev)
VirtQueueElement *elem;
VirtIODevice *vdev = VIRTIO_DEVICE(dev);
VirtQueue *vq = dev->free_page_vq;
bool ret = true;
while (dev->block_iothread) {
qemu_cond_wait(&dev->free_page_cond, &dev->free_page_lock);
@ -405,13 +406,12 @@ static bool get_free_page_hints(VirtIOBalloon *dev)
uint32_t id;
size_t size = iov_to_buf(elem->out_sg, elem->out_num, 0,
&id, sizeof(id));
virtqueue_push(vq, elem, size);
g_free(elem);
virtio_tswap32s(vdev, &id);
if (unlikely(size != sizeof(id))) {
virtio_error(vdev, "received an incorrect cmd id");
return false;
ret = false;
goto out;
}
if (id == dev->free_page_report_cmd_id) {
dev->free_page_report_status = FREE_PAGE_REPORT_S_START;
@ -431,11 +431,12 @@ static bool get_free_page_hints(VirtIOBalloon *dev)
qemu_guest_free_page_hint(elem->in_sg[0].iov_base,
elem->in_sg[0].iov_len);
}
virtqueue_push(vq, elem, 1);
g_free(elem);
}
return true;
out:
virtqueue_push(vq, elem, 1);
g_free(elem);
return ret;
}
static void virtio_ballloon_get_free_page_hints(void *opaque)