netdev - Re: [PATCH] net: netcp: Fix crash in error path when DMA channel open fails

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Message-ID: <08a13fb0-dd12-491e-98af-ef67d55cc403@ti.com>
Date: Fri, 26 Sep 2025 22:28:47 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Simon Horman <horms@...nel.org>
CC: Nishanth Menon <nm@...com>,
        Uwe Kleine-König
	<u.kleine-koenig@...libre.com>,
        Paolo Abeni <pabeni@...hat.com>, Jakub
 Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S.
 Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew+netdev@...n.ch>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, <s-vadapalli@...com>
Subject: Re: [PATCH] net: netcp: Fix crash in error path when DMA channel open
 fails

On 26/09/25 10:12 PM, Simon Horman wrote:
> On Fri, Sep 26, 2025 at 09:57:02PM +0530, Siddharth Vadapalli wrote:
>> On 26/09/25 9:43 PM, Simon Horman wrote:
>>> On Fri, Sep 26, 2025 at 10:08:53AM -0500, Nishanth Menon wrote:
>>>> When knav_dma_open_channel() fails in netcp_setup_navigator_resources(),
>>>> the rx_channel field is set to an ERR_PTR value. Later, when
>>>> netcp_free_navigator_resources() is called in the error path, it attempts
>>>> to close this invalid channel pointer, causing a crash.
>>>>
>>>> Add a check for ERR values to handle the failure scenario.
>>>>
>>>> Fixes: 84640e27f230 ("net: netcp: Add Keystone NetCP core driver")
>>>> Signed-off-by: Nishanth Menon <nm@...com>
>>>> ---
>>>>
>>>> Seen on kci log for k2hk: https://dashboard.kernelci.org/log-viewer?itemId=ti%3A2eb55ed935eb42c292e02f59&org=ti&type=test&url=http%3A%2F%2Ffiles.kernelci.org%2F%2Fti%2Fmainline%2Fmaster%2Fv6.17-rc7-59-gbf40f4b87761%2Farm%2Fmulti_v7_defconfig%2BCONFIG_EFI%3Dy%2BCONFIG_ARM_LPAE%3Dy%2Bdebug%2Bkselftest%2Btinyconfig%2Fgcc-12%2Fbaseline-nfs-boot.nfs-k2hk-evm.txt.gz
>>>>
>>>>    drivers/net/ethernet/ti/netcp_core.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/ti/netcp_core.c b/drivers/net/ethernet/ti/netcp_core.c
>>>> index 857820657bac..4ff17fd6caae 100644
>>>> --- a/drivers/net/ethernet/ti/netcp_core.c
>>>> +++ b/drivers/net/ethernet/ti/netcp_core.c
>>>> @@ -1549,7 +1549,7 @@ static void netcp_free_navigator_resources(struct netcp_intf *netcp)
>>>>    {
>>>>    	int i;
>>>> -	if (netcp->rx_channel) {
>>>> +	if (!IS_ERR(netcp->rx_channel)) {
>>>>    		knav_dma_close_channel(netcp->rx_channel);
>>>>    		netcp->rx_channel = NULL;
>>>>    	}
>>>
>>> Hi Nishanth,
>>>
>>> Thanks for your patch.
>>>
>>> I expect that netcp_txpipe_close() has a similar problem too.
>>>
>>> But I also think that using IS_ERR is not correct, because it seems to me
>>> that there are also cases where rx_channel can be NULL.
>>
>> Could you please clarify where rx_channel is NULL? rx_channel is set by
>> invoking knav_dma_open_channel().
> 
> Hi Siddharth,
> 
> I am assuming that when netcp_setup_navigator_resources() is called, at
> least for the first time, that netcp->rx_channel is NULL. So any of the
> occurrence of 'goto fail' in that function before the call to
> knav_dma_open_channel().

I missed this. Thank you for pointing this out.

> 
>> Also, please refer to:
>> https://github.com/torvalds/linux/commit/5b6cb43b4d62
>> which specifically points out that knav_dma_open_channel() will not return
>> NULL so the check for NULL isn't required.
>>>
>>> I see that on error knav_dma_open_channel() always returns ERR_PTR(-EINVAL)
>>> (open coded as (void *)-EINVAL) on error. So I think a better approach
>>> would be to change knav_dma_open_channel() to return NULL, and update callers
>>> accordingly.
>>
>> The commit referred to above made changes to the driver specifically due to
>> the observation that knav_dma_open_channel() never returns NULL. Modifying
>> knav_dma_open_channel() to return NULL will effectively result in having to
>> undo the changes made by the commit.
> 
> I wasn't aware of that patch. But my observation is that the return value
> of knav_dma_open_channel() is still not handled correctly. E.g. the bug
> your patch is fixing.  And I'm proposing an alternate approach which I feel
> will be less error-prone.

Ok. If I understand correctly, you are proposing that the 'error codes' 
returned by knav_dma_open_channel() should be turned into a dev_err() 
print for the user and knav_dma_open_channel() should always return NULL 
in case of failure and a pointer to the channel in case of success. Is 
that right?