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

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Message-ID: <aNbCgK76kQqhcQY2@horms.kernel.org>
Date: Fri, 26 Sep 2025 17:42:40 +0100
From: Simon Horman <horms@...nel.org>
To: Siddharth Vadapalli <s-vadapalli@...com>
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
Subject: Re: [PATCH] net: netcp: Fix crash in error path when DMA channel
 open fails

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().

> 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.