A buffer overflow vulnerability in mipsnet_ioport_write() function was found.

Vulnerable code (hw/net/mipsnet.c):

static void mipsnet_ioport_write(void *opaque, hwaddr addr,
uint64_t val, unsigned int size)
{
MIPSnetState *s = opaque;

addr &= 0x3f;
trace_mipsnet_write(addr, val);
switch (addr) {
case MIPSNET_TX_DATA_COUNT:
s->tx_count = (val <= MAX_ETH_FRAME_SIZE) ? val : 0;// set tx_count=0
s->tx_written = 0;
break;
...
case MIPSNET_TX_DATA_BUFFER:
s->tx_buffer[s->tx_written++] = val;
if (s->tx_written == s->tx_count) { // never get executed, causes the s->tx_buffer to overflow
/* Send buffer. */
trace_mipsnet_send(s->tx_count);
qemu_send_packet(qemu_get_queue(s->nic), s->tx_buffer, s->tx_count);
s->tx_count = s->tx_written = 0;
s->intctl |= MIPSNET_INTCTL_TXDONE;
s->busy = 1;
mipsnet_update_irq(s);
}
...
}

s->tx_written can exceed the MAX_ETH_FRAME_SIZE causing s->tx_buffer to overflow.