From 92504013c1489168e3514f3c7342c016156c6af3 Mon Sep 17 00:00:00 2001 From: Michael S. Tsirkin Date: Wed, 19 Mar 2014 17:21:02 +0200 Subject: [PATCH] virtio-net: fix guest-triggerable buffer overrun RH-Author: Michael S. Tsirkin Message-id: <1395242197-28749-1-git-send-email-mst@redhat.com> O-Subject: [virt-devel][PATCH EMBARGOED qemu-kvm RHEL7.0] virtio-net: fix Bugzilla: 1078308 RH-Acked-by: Markus Armbruster RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Vlad Yasevich RH-Acked-by: Dr. David Alan Gilbert When VM guest programs multicast addresses for a virtio net card, it supplies a 32 bit entries counter for the number of addresses. These addresses are read into tail portion of a fixed macs array which has size MAC_TABLE_ENTRIES, at offset equal to in_use. To avoid overflow of this array by guest, qemu attempts to test the size as follows: - if (in_use + mac_data.entries <= MAC_TABLE_ENTRIES) { however, as mac_data.entries is uint32_t, this sum can overflow, e.g. if in_use is 1 and mac_data.entries is 0xffffffff then in_use + mac_data.entries will be 0. Qemu will then read guest supplied buffer into this memory, overflowing buffer on heap. Signed-off-by: Michael S. Tsirkin Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1078308 Upstream status: EMBARGOED RT 284849 Brew build: http://brewweb.devel.redhat.com/brew/taskinfo?taskID=7225956 --- hw/net/virtio-net.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index 06c53fe..2d559e0 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -594,7 +594,7 @@ static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd, goto error; } - if (in_use + mac_data.entries <= MAC_TABLE_ENTRIES) { + if (mac_data.entries <= MAC_TABLE_ENTRIES - in_use) { s = iov_to_buf(iov, iov_cnt, 0, &macs[in_use * ETH_ALEN], mac_data.entries * ETH_ALEN); if (s != mac_data.entries * ETH_ALEN) { -- 1.7.1