Fix possible OOB during queuing packets

We try to detect and drop too large packet (>INT_MAX) in 1592a9947036 ("net: ignore packet size greater than INT_MAX") during packet delivering. Unfortunately, this is not sufficient as we may hit another integer overflow when trying to queue such large packet in qemu_net_queue_append_iov():

- size of the allocation may overflow on 32bit
- packet->size is integer which may overflow even on 64bit

Fixing this by moving the check to qemu_sendv_packet_async() which is the entrance of all networking codes and reduce the limit to NET_BUFSIZE to be more conservative. This works since:

- For the callers that call qemu_sendv_packet_async() directly, they only care about if zero is returned to determine whether to prevent the source from producing more packets. A callback will be triggered if peer can accept more then source could be enabled. This is usually used by high speed networking implementation like virtio-net or netmap.
- For the callers that call qemu_sendv_packet() that calls qemu_sendv_packet_async() indirectly, they often ignore the return value. In this case qemu will just the drop packets if peer can't receive.

Qemu will copy the packet if it was queued. So it was safe for both kinds of the callers to assume the packet was sent.

Since we move the check from qemu_deliver_packet_iov() to qemu_sendv_packet_async(), it would be safer to make qemu_deliver_packet_iov() static to prevent any external user in the future.

This is a revised patch of CVE-2018-17963.

Cc [email protected]

Cc Li Qiang <[email protected]>

Fixes 1592a9947036 ("net: ignore packet size greater than INT_MAX")

Reported-by Li Qiang <[email protected]>

Reviewed-by Li Qiang <[email protected]>

Signed-off-by Jason Wang <[email protected]>

---
 include/net/net.h |  6 ------
 net/net.c         | 28 +++++++++++++++++-----------
 2 files changed, 17 insertions(+), 17 deletions(-)

include/net/net.h +0 -6

index 7936d53d2f..ec13702dbf 100644
@@ -169,12 +169,6 @@ void qemu_check_nic_model(NICInfo *nd, const char *model);
 int qemu_find_nic_model(NICInfo *nd, const char * const *models,
                         const char *default_model);
 
-ssize_t qemu_deliver_packet_iov(NetClientState *sender,
-                            unsigned flags,
-                            const struct iovec *iov,
-                            int iovcnt,
-                            void *opaque);
-
 void print_net_client(Monitor *mon, NetClientState *nc);
 void hmp_info_network(Monitor *mon, const QDict *qdict);
 void net_socket_rs_init(SocketReadState *rs,

net/net.c +12 -10

index 07c194a8f6..1f7d626197 100644
@@ -231,6 +231,11 @@ static void qemu_net_client_destructor(NetClientState *nc)
 {
     g_free(nc);
 }
+static ssize_t qemu_deliver_packet_iov(NetClientState *sender,
+                                       unsigned flags,
+                                       const struct iovec *iov,
+                                       int iovcnt,
+                                       void *opaque);
 
 static void qemu_net_client_setup(NetClientState *nc,
                                   NetClientInfo *info,

@@ -705,22 +710,18 @@ static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec *iov,
     return ret;
 }
 
-ssize_t qemu_deliver_packet_iov(NetClientState *sender,
-                                unsigned flags,
-                                const struct iovec *iov,
-                                int iovcnt,
-                                void *opaque)
+static ssize_t qemu_deliver_packet_iov(NetClientState *sender,
+                                       unsigned flags,
+                                       const struct iovec *iov,
+                                       int iovcnt,
+                                       void *opaque)
 {
     NetClientState *nc = opaque;
-    size_t size = iov_size(iov, iovcnt);
     int ret;
 
-    if (size > INT_MAX) {
-        return size;
-    }
 
     if (nc->link_down) {
-        return size;
+        return iov_size(iov, iovcnt);
     }
 
     if (nc->receive_disabled) {

@@ -745,10 +746,15 @@ ssize_t qemu_sendv_packet_async(NetClientState *sender,
                                 NetPacketSent *sent_cb)
 {
     NetQueue *queue;
+    size_t size = iov_size(iov, iovcnt);
     int ret;
 

If we want to qtest through hub, it would be much more simpler and safer to configure the hub without host network. So silent this warnings for qtest.

Signed-off-by Jason Wang <[email protected]>

---
 net/hub.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

net/hub.c +1 -0

index 78b671ed95..5795a678ed 100644
@@ -20,6 +20,7 @@
 #include "hub.h"
 #include "qemu/iov.h"
 #include "qemu/error-report.h"
+#include "sysemu/qtest.h"
 
 /*
  * A hub broadcasts incoming packets to all its ports except the source port.

This test tries to build a packet whose size is greater than INT_MAX which tries to trigger integer overflow in qemu_net_queue_append_iov() which may result OOB.

Signed-off-by Jason Wang <[email protected]>

---
 tests/virtio-net-test.c | 46 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

tests/virtio-net-test.c +42 -0

index bdd6af9999..e9783e6707 100644
@@ -245,6 +245,48 @@ static void pci_basic(gconstpointer data)
     g_free(dev);
     qtest_shutdown(qs);
 }
+
+static void large_tx(gconstpointer data)
+{
+    QVirtioPCIDevice *dev;
+    QOSState *qs;
+    QVirtQueuePCI *tx, *rx;
+    QVirtQueue *vq;
+    uint64_t req_addr;
+    uint32_t free_head;
+    size_t alloc_size = (size_t)data / 64;
+    int i;
+
+    qs = pci_test_start("-netdev hubport,id=hp0,hubid=0 "
+                        "-device virtio-net-pci,netdev=hp0");
+    dev = virtio_net_pci_init(qs->pcibus, PCI_SLOT);
+
+    rx = (QVirtQueuePCI *)qvirtqueue_setup(&dev->vdev, qs->alloc, 0);
+    tx = (QVirtQueuePCI *)qvirtqueue_setup(&dev->vdev, qs->alloc, 1);
+
+    driver_init(&dev->vdev);
+    vq = &tx->vq;
+
+    /* Bypass the limitation by pointing several descriptors to a single
+     * smaller area */
+    req_addr = guest_alloc(qs->alloc, alloc_size);
+    free_head = qvirtqueue_add(vq, req_addr, alloc_size, false, true);
+
+    for (i = 0; i < 64; i++) {
+        qvirtqueue_add(vq, req_addr, alloc_size, false, i != 63);
+    }
+    qvirtqueue_kick(&dev->vdev, vq, free_head);
+
+    qvirtio_wait_used_elem(&dev->vdev, vq, free_head, NULL,
+                           QVIRTIO_NET_TIMEOUT_US);
+
+    qvirtqueue_cleanup(dev->vdev.bus, &tx->vq, qs->alloc);
+    qvirtqueue_cleanup(dev->vdev.bus, &rx->vq, qs->alloc);
+    qvirtio_pci_device_disable(dev);
+    g_free(dev->pdev);
+    g_free(dev);
+    qtest_shutdown(qs);
+}
 #endif
 
 static void hotplug(void)

Hi:

This series tries to fix a possible OOB during queueing packets through qemu_net_queue_append_iov(). This could happen when it tries to queue a packet whose size is larger than INT_MAX which may lead integer overflow. We've fixed similar issue in the past during qemu_net_queue_deliver_iov() by ignoring large packets there. Let's just move the check earlier to qemu_sendv_packet_async() and reduce the limitation to NET_BUFSIZE. A simple qtest were also added this.

Please review.

Thanks

Changes from V1:
- slient compiling warnings
Changes from V2:
- annotate pci_test_start() with GCC_FMT_ATTR()
- drop intermediate cmd string variable
Changes from V4:
- silent hub warning if qtest is enabled
- make qemu_deliver_packet_iov() static
- add one more test for packet size slightly greater than NET_BUFSIZE
- tweak the commit log and add more justification
- typo/whitespace fixes and other minor code style tweaks

Jason Wang (5):
net: drop too large packet early
net: hub: suppress warnings of no host network for qtest
virtio-net-test: accept variable length argument in pci_test_start()
virtio-net-test: remove unused macro
virtio-net-test: add large tx buffer test