hw/net/xgmac: Fix buffer overflow in xgmac_enet_send()

A buffer overflow issue was reported by Mr. Ziming Zhang, CC'd here. It
occurs while sending an Ethernet frame due to missing break statements
and improper checking of the buffer size.

Reported-by: Ziming Zhang <ezrakiez@gmail.com>
Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>

diff --git a/hw/net/xgmac.c b/hw/net/xgmac.c
index 574dd47b412fef025943f8e4b8be23bd6829db02..5bf1b6101242d0922ece06ec50fc5e877bce0314 100644 (file)
--- a/hw/net/xgmac.c
+++ b/hw/net/xgmac.c
@@ -220,21 +220,31 @@ static void xgmac_enet_send(XgmacState *s)
         }
         len = (bd.buffer1_size & 0xfff) + (bd.buffer2_size & 0xfff);
 
+        /*
+         * FIXME: these cases of malformed tx descriptors (bad sizes)
+         * should probably be reported back to the guest somehow
+         * rather than simply silently stopping processing, but we
+         * don't know what the hardware does in this situation.
+         * This will only happen for buggy guests anyway.
+         */
         if ((bd.buffer1_size & 0xfff) > 2048) {
             DEBUGF_BRK("qemu:%s:ERROR...ERROR...ERROR... -- "
                         "xgmac buffer 1 len on send > 2048 (0x%x)\n",
                          __func__, bd.buffer1_size & 0xfff);
+            break;
         }
         if ((bd.buffer2_size & 0xfff) != 0) {
             DEBUGF_BRK("qemu:%s:ERROR...ERROR...ERROR... -- "
                         "xgmac buffer 2 len on send != 0 (0x%x)\n",
                         __func__, bd.buffer2_size & 0xfff);
+            break;
         }
-        if (len >= sizeof(frame)) {
+        if (frame_size + len >= sizeof(frame)) {
             DEBUGF_BRK("qemu:%s: buffer overflow %d read into %zu "
-                        "buffer\n" , __func__, len, sizeof(frame));
+                        "buffer\n" , __func__, frame_size + len, sizeof(frame));
             DEBUGF_BRK("qemu:%s: buffer1.size=%d; buffer2.size=%d\n",
                         __func__, bd.buffer1_size, bd.buffer2_size);
+            break;
         }
 
         cpu_physical_memory_read(bd.buffer1_addr, ptr, len);