linux-kernel - Re: [PATCH v1] gve: fix zero size queue page list allocation

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Date:   Mon, 14 Feb 2022 21:31:27 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Wang, Haiyue" <haiyue.wang@...el.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jeroen de Borst <jeroendb@...gle.com>,
        Catherine Sullivan <csully@...gle.com>,
        "David Awogbemila" <awogbemila@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        "Forrest, Bailey" <bcf@...gle.com>, Tao Liu <xliutaox@...gle.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        John Fraker <jfraker@...gle.com>,
        "Yangchun Fu" <yangchun@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] gve: fix zero size queue page list allocation

On Tue, 15 Feb 2022 05:25:49 +0000 Wang, Haiyue wrote:
> > On Mon, 14 Feb 2022 10:41:29 +0800 Haiyue Wang wrote:  
> > > According to the two functions 'gve_num_tx/rx_qpls', only the queue with
> > > GVE_GQI_QPL_FORMAT format has queue page list.
> > >
> > > The 'queue_format == GVE_GQI_RDA_FORMAT' may lead to request zero sized
> > > memory allocation, like if the queue format is GVE_DQO_RDA_FORMAT.
> > >
> > > The kernel memory subsystem will return ZERO_SIZE_PTR, which is not NULL
> > > address, so the driver can run successfully. Also the code still checks
> > > the queue page list number firstly, then accesses the allocated memory,
> > > so zero number queue page list allocation will not lead to access fault.
> > >
> > > Use the queue page list number to detect no QPLs, it can avoid zero size
> > > queue page list memory allocation.  
> > 
> > There's no bug here, strictly speaking, the driver will function
> > correctly? In that case please repost without the Fixes tag and  
> 
> Code design bug, the 'queue_format == GVE_GQI_RDA_FORMAT' is not correct. But,
> yes, it works. So still need to remove the tag ?

A bug is something that users can notice. If there are conditions under
which this may lead to user-visible mis-behavior then we should keep
the tag and send the patch to stable as well.

If there is no user-visible problem here, then the patch is just
future-proofing / refactoring and we should not risk introducing real
bugs by making people backport it (which is what adding a Fixes will
do).