Re: [PATCH iwl-net] idpf: fix RSS LUT memcpy size

[Larysa Zaremba <larysa.zaremba@intel.com>]

On Thu, Apr 30, 2026 at 09:38:44AM -0700, Jacob Keller wrote:
> On 4/29/2026 12:42 AM, Larysa Zaremba wrote:
> > Based on the following feedback from Sashiko (received for iXD phase 1
> > patchset, but valid for the net tree):
> > 
> >  "Is the bounds check xn_params.recv_mem.iov_len < lut_buf_size sufficient?
> >   Since lut_buf_size only represents the size of the array elements, should
> >   this check instead verify that the payload is at least
> >   sizeof(struct virtchnl2_rss_lut) + lut_buf_size?
> > 
> >   [...]
> > 
> >   Does memcpy copy the correct amount of data here? rss_lut_size stores the
> >   number of 32-bit entries, not the size in bytes. Should it use
> >   lut_buf_size or rss_data->rss_lut_size * sizeof(u32) instead?"
> > 
> > After inspecting the code, it was concluded that RSS memcpy size is in fact
> > 4 times smaller than it has to be, since a single array entry in a u32, and
> > rss_data->rss_lut_size is clearly used as an array size. Required Rx buffer
> > size is also too small, but this is a common issue in the idpf code.
> > 
> > Use a full buffer size (lut_buf_size) instead of the array length
> > (rss_data->rss_lut_size) when doing memcpy of RSS lookup table.
> > While at it, increase required Rx buffer size to a whole flex-array
> > containing structure instead of just the array.
> > 
> > Link: https://sashiko.dev/#/patchset/20260323174052.5355-1-larysa.zaremba%40intel.com?part=8
> > Fixes: 95af467d9a4e ("idpf: configure resources for RX queues")
> > Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
> > Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> > ---
> >  drivers/net/ethernet/intel/idpf/idpf_virtchnl.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> > index be66f9b2e101..a97d2e9b54d4 100644
> > --- a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> > +++ b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> > @@ -2916,7 +2916,7 @@ int idpf_send_get_set_rss_lut_msg(struct idpf_adapter *adapter,
> >  		return -EIO;
> >  
> >  	lut_buf_size = le16_to_cpu(recv_rl->lut_entries) * sizeof(u32);
> > -	if (reply_sz < lut_buf_size)
> > +	if (reply_sz < lut_buf_size + sizeof(struct virtchnl2_rss_lut))
> 
> This feels like it should be using struct_size or flex_array_size...
> 

struct_size() does not really fit here, as lut_buf_size is needed later for 
flex-array-only memcpy, but flex_array_size() I can use.

> >  		return -EIO;
> >  
> >  	/* size didn't change, we can reuse existing lut buf */
> > @@ -2933,7 +2933,7 @@ int idpf_send_get_set_rss_lut_msg(struct idpf_adapter *adapter,
> >  	}
> >  
> >  do_memcpy:
> > -	memcpy(rss_data->rss_lut, recv_rl->lut, rss_data->rss_lut_size);
> > +	memcpy(rss_data->rss_lut, recv_rl->lut, lut_buf_size);
> >  
> >  	return 0;
> >  }
>