Re: [PATCH] net: nvidia: forcedeth: Fix two possible concurrency use-after-free bugs

[Jia-Ju Bai]

On 2019/1/9 9:24, Yanjun Zhu wrote:
> On 2019/1/8 20:57, Jia-Ju Bai wrote:
> > On 2019/1/8 20:54, Zhu Yanjun wrote:
> > > å 2019/1/8 20:45, Jia-Ju Bai åé:
> > > > In drivers/net/ethernet/nvidia/forcedeth.c, the functions
> > > > nv_start_xmit() and nv_start_xmit_optimized() can be concurrently
> > > > executed with nv_poll_controller().
> > > >
> > > > nv_start_xmit
> > > >    line 2321: prev_tx_ctx->skb = skb;
> > > >
> > > > nv_start_xmit_optimized
> > > >    line 2479: prev_tx_ctx->skb = skb;
> > > >
> > > > nv_poll_controller
> > > >    nv_do_nic_poll
> > > >      line 4134: spin_lock(&np->lock);
> > > >      nv_drain_rxtx
> > > >        nv_drain_tx
> > > >          nv_release_txskb
> > > >            line 2004: dev_kfree_skb_any(tx_skb->skb);
> > > >
> > > > Thus, two possible concurrency use-after-free bugs may occur.
> > > >
> > > > To fix these possible bugs,
> > >
> > >
> > > Does this really occur? Can you reproduce this ?
> >
> > This bug is not found by the real execution.
> > It is found by a static tool written by myself, and then I check it 
> > by manual code review.
>
> Before "line 2004: dev_kfree_skb_any(tx_skb->skb); ",
>
> "
>
>                 nv_disable_irq(dev);
>                 nv_napi_disable(dev);
>                 netif_tx_lock_bh(dev);
>                 netif_addr_lock(dev);
>                 spin_lock(&np->lock);
>                 /* stop engines */
>                 nv_stop_rxtx(dev);   <---this stop rxtx
>                 nv_txrx_reset(dev);
> "
>
> In this case, does nv_start_xmit or nv_start_xmit_optimized still work 
> well?

nv_stop_rxtx() calls nv_stop_tx(dev).

static void nv_stop_tx(struct net_device *dev)
{
    struct fe_priv *np = netdev_priv(dev);
    u8 __iomem *base = get_hwbase(dev);
    u32 tx_ctrl = readl(base + NvRegTransmitterControl);

    if (!np->mac_in_use)
        tx_ctrl &= ~NVREG_XMITCTL_START;
    else
        tx_ctrl |= NVREG_XMITCTL_TX_PATH_EN;
    writel(tx_ctrl, base + NvRegTransmitterControl);
    if (reg_delay(dev, NvRegTransmitterStatus, NVREG_XMITSTAT_BUSY, 0,
              NV_TXSTOP_DELAY1, NV_TXSTOP_DELAY1MAX))
        netdev_info(dev, "%s: TransmitterStatus remained busy\n",
                __func__);

    udelay(NV_TXSTOP_DELAY2);
    if (!np->mac_in_use)
        writel(readl(base + NvRegTransmitPoll) & 
NVREG_TRANSMITPOLL_MAC_ADDR_REV,
               base + NvRegTransmitPoll);
}

nv_stop_tx() seems to only write registers to stop transmitting for 
hardware.
But it does not wait until nv_start_xmit() and nv_start_xmit_optimized() 
finish execution.
Maybe netif_stop_queue() should be used here to stop transmitting for 
network layer, but this function does not seem to wait, either.
Do you know any function that can wait until ".ndo_start_xmit" finish 
execution?


Best wishes,
Jia-Ju Bai