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Subject: Re: [PATCH] net: nvidia: forcedeth: Fix two possible concurrency
 use-after-free bugs
To:     Yanjun Zhu <yanjun.zhu@oracle.com>, davem@davemloft.net,
        keescook@chromium.org
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20190108124518.21986-1-baijiaju1990@gmail.com>
 <27392ae0-2c0f-f099-05d8-f9cdbfbd313e@oracle.com>
 <f9ab7ba3-573c-6703-1b01-37a9e0a9b769@gmail.com>
 <f87bd4b7-81d5-1f0c-137e-ecbc02753257@oracle.com>
 <a1a71d06-9c1c-7e18-0e24-103fa89facf2@gmail.com>
 <a861dacb-c992-13d7-5458-09445183655b@oracle.com>
From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Message-ID: <54c2efce-18ac-46d4-7fb5-8510699b528e@gmail.com>
Date:   Wed, 9 Jan 2019 11:20:52 +0800
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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:
>>>>>
>>>>> 在 2019/1/8 20:45, Jia-Ju Bai 写道:
>>>>>> 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.
> 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 :)


Best wishes,
Jia-Ju Bai