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

[Yanjun Zhu]

On 2019/1/9 10:03, Jia-Ju Bai wrote:
> 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
> > > > > ÂÂ line 2321: prev_tx_ctx->skb = skb;
> > > > >
> > > > > nv_start_xmit_optimized
> > > > > ÂÂ line 2479: prev_tx_ctx->skb = skb;
> > > > >
> > > > > nv_poll_controller
> > > > > ÂÂ nv_do_nic_poll
> > > > > ÂÂÂÂ line 4134: spin_lock(&np->lock);
> > > > > ÂÂÂÂ nv_drain_rxtx
> > > > > ÂÂÂÂÂÂ nv_drain_tx
> > > > > ÂÂÂÂÂÂÂÂ nv_release_txskb
> > > > > ÂÂÂÂÂÂÂÂÂÂ 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); ",
> >
> > "
> >
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ nv_disable_irq(dev);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ nv_napi_disable(dev);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ netif_tx_lock_bh(dev);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ netif_addr_lock(dev);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ spin_lock(&np->lock);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ /* stop engines */
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ nv_stop_rxtx(dev);ÂÂ <---this stop rxtx
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 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)
> {
> ÂÂÂ struct fe_priv *np = netdev_priv(dev);
> ÂÂÂ u8 __iomem *base = get_hwbase(dev);
> ÂÂÂ u32 tx_ctrl = readl(base + NvRegTransmitterControl);
>
> ÂÂÂ if (!np->mac_in_use)
> ÂÂÂÂÂÂÂ tx_ctrl &= ~NVREG_XMITCTL_START;
> ÂÂÂ else
> ÂÂÂÂÂÂÂ tx_ctrl |= NVREG_XMITCTL_TX_PATH_EN;
> ÂÂÂ writel(tx_ctrl, base + NvRegTransmitterControl);
> ÂÂÂ if (reg_delay(dev, NvRegTransmitterStatus, NVREG_XMITSTAT_BUSY, 0,
> ÂÂÂÂÂÂÂÂÂÂÂÂÂ NV_TXSTOP_DELAY1, NV_TXSTOP_DELAY1MAX))
> ÂÂÂÂÂÂÂ netdev_info(dev, "%s: TransmitterStatus remained busy\n",
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ __func__);
>
> ÂÂÂ udelay(NV_TXSTOP_DELAY2);
> ÂÂÂ if (!np->mac_in_use)
> ÂÂÂÂÂÂÂ writel(readl(base + NvRegTransmitPoll) & 
> NVREG_TRANSMITPOLL_MAC_ADDR_REV,
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 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.
There are 3 modes in forcedeth NIC.
In throughput mode (0), every tx & rx packet will generate an interrupt.
In CPU mode (1), interrupts are controlled by a timer.
In dynamic mode (2), the mode toggles between throughput and CPU mode 
based on network load.

From the source code,

"np->recover_error = 1;" is related with CPU mode.

nv_start_xmit or nv_start_xmit_optimized seems related with ghroughput mode.

In static void nv_do_nic_poll(struct timer_list *t),
when if (np->recover_error), line 2004: dev_kfree_skb_any(tx_skb->skb); 
will run.

When "np->recover_error=1", do you think nv_start_xmit or 
nv_start_xmit_optimized will be called?


> 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