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

[Yanjun Zhu]

On 2019/1/9 11:20, Jia-Ju Bai wrote:
> On 2019/1/9 10:35, Yanjun Zhu wrote:
> > 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?
>
> Sorry, I do not know about these modes...
> But I still think nv_start_xmit() or nv_start_xmit_optimized() can be 
> called here, in no matter which mode :)


:-P

If you have forcedeth NIC, you can make tests with it.:-)
> Best wishes,
> Jia-Ju Bai