Subject: Re: [PATCH][next] iavf: Replace one-element array with flexible-array member

From: Kees Cook <[email-masked]>
Date: Fri, 26 May 2023 14:00:50 -0700

On Tue, May 23, 2023 at 11:19:00AM -0700, Tony Nguyen wrote:
> On 5/15/2023 5:44 PM, Gustavo A. R. Silva wrote:
> > One-element arrays are deprecated, and we are replacing them with flexible
> > array members instead. So, replace one-element array with flexible-array
> > member in struct iavf_qvlist_info, and refactor the rest of the code,
> > accordingly.
> > 
> > This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> > routines on memcpy() and help us make progress towards globally
> > enabling -fstrict-flex-arrays=3 [1].
> > 
> > Link: https://github.com/KSPP/linux/issues/79
> > Link: https://github.com/KSPP/linux/issues/289
> > Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> > Signed-off-by: Gustavo A. R. Silva <[email-masked]>
> > ---
> >   drivers/net/ethernet/intel/iavf/iavf_client.c | 2 +-
> >   drivers/net/ethernet/intel/iavf/iavf_client.h | 2 +-
> >   2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/iavf/iavf_client.c b/drivers/net/ethernet/intel/iavf/iavf_client.c
> > index 93c903c02c64..782384b3aa38 100644
> > --- a/drivers/net/ethernet/intel/iavf/iavf_client.c
> > +++ b/drivers/net/ethernet/intel/iavf/iavf_client.c
> > @@ -470,7 +470,7 @@ static int iavf_client_setup_qvlist(struct iavf_info *ldev,
> >   	v_qvlist_info = (struct virtchnl_rdma_qvlist_info *)qvlist_info;
> >   	msg_size = struct_size(v_qvlist_info, qv_info,
> > -			       v_qvlist_info->num_vectors - 1);
> > +			       v_qvlist_info->num_vectors);
> 
> The problem is this mirrors the virtchnl struct (virtchnl_rdma_qvlist_info)
> so that structure needs to change as well... However, this goes back to the
> interface that virtchnl provides between PF and VF [1].
> 
> I think removing the iavf structure and directly using the virtchnl one
> would make sense. We'd need to adjust virtchnl and follow Kees' suggestion
> [2].

Note that at the time I suggested "[0]", but it should have been
"[]". But, yes, Keeping the "over allocation" is fine since it's a
hardware ABI.

Alternatively, it could be defined with a union to keep all the sizes
the same:

 struct iavf_qvlist_info {
 	u32 num_vectors;
-	struct iavf_qv_info qv_info[1];
+	union {
+		struct iavf_qv_info single_qv_info;
+		DECLARE_FLEX_ARRAY(struct iavf_qv_info, qv_info)
+	};
 };

-Kees

> 
> >   	adapter->client_pending |= BIT(VIRTCHNL_OP_CONFIG_RDMA_IRQ_MAP);
> >   	err = iavf_aq_send_msg_to_pf(&adapter->hw,
> > diff --git a/drivers/net/ethernet/intel/iavf/iavf_client.h b/drivers/net/ethernet/intel/iavf/iavf_client.h
> > index c5d51d7dc7cc..500269bc0f5b 100644
> > --- a/drivers/net/ethernet/intel/iavf/iavf_client.h
> > +++ b/drivers/net/ethernet/intel/iavf/iavf_client.h
> > @@ -53,7 +53,7 @@ struct iavf_qv_info {
> >   struct iavf_qvlist_info {
> >   	u32 num_vectors;
> > -	struct iavf_qv_info qv_info[1];
> > +	struct iavf_qv_info qv_info[];
> >   };
> >   #define IAVF_CLIENT_MSIX_ALL 0xFFFFFFFF
> 
> [1] https://lore.kernel.org/intel-wired-lan/[email-masked]/
> [2] https://lore.kernel.org/intel-wired-lan/202106091424.37E833794@keescook/

-- 
Kees Cook