From 4bf58c7213b0ab03209a53731c71f0861c35ef91 Mon Sep 17 00:00:00 2001 From: Wentao Liang Date: Thu, 7 Apr 2022 05:51:59 -0400 Subject: [PATCH] virtio-iommu: use-after-free fix MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit A potential Use-after-free was reported in virtio_iommu_handle_command when using virtio-iommu: > I find a potential Use-after-free in QEMU 6.2.0, which is in > virtio_iommu_handle_command() (./hw/virtio/virtio-iommu.c). > > > Specifically, in the loop body, the variable 'buf' allocated at line 639 can be > freed by g_free() at line 659. However, if the execution path enters the loop > body again and the if branch takes true at line 616, the control will directly > jump to 'out' at line 651. At this time, 'buf' is a freed pointer, which is not > assigned with an allocated memory but used at line 653. As a result, a UAF bug > is triggered. > > > > 599 for (;;) { > ... > 615 sz = iov_to_buf(iov, iov_cnt, 0, &head, sizeof(head)); > 616 if (unlikely(sz != sizeof(head))) { > 617 tail.status = VIRTIO_IOMMU_S_DEVERR; > 618 goto out; > 619 } > ... > 639 buf = g_malloc0(output_size); > ... > 651 out: > 652 sz = iov_from_buf(elem->in_sg, elem->in_num, 0, > 653 buf ? buf : &tail, output_size); > ... > 659 g_free(buf); > > We can fix it by set ‘buf‘ to NULL after freeing it: > > > 651 out: > 652 sz = iov_from_buf(elem->in_sg, elem->in_num, 0, > 653 buf ? buf : &tail, output_size); > ... > 659 g_free(buf); > +++ buf = NULL; > 660 } Fix as suggested by the reporter. Signed-off-by: Wentao Liang Signed-off-by: Michael S. Tsirkin Message-id: 20220407095047.50371-1-mst@redhat.com Message-ID: <20220406040445-mutt-send-email-mst@kernel.org> Signed-off-by: Peter Maydell --- hw/virtio/virtio-iommu.c | 1 + 1 file changed, 1 insertion(+) diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c index 664cbd9583..6d5ea0bdf1 100644 --- a/hw/virtio/virtio-iommu.c +++ b/hw/virtio/virtio-iommu.c @@ -683,6 +683,7 @@ out: virtio_notify(vdev, vq); g_free(elem); g_free(buf); + buf = NULL; } }