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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>
From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Message-ID: <a1a71d06-9c1c-7e18-0e24-103fa89facf2@gmail.com>
Date:   Wed, 9 Jan 2019 10:03:30 +0800
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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.
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