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

[Jacob Keller <jacob.e.keller@intel.com>]

On 5/4/2026 6:26 AM, Larysa Zaremba wrote:
> 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.
> 

Right. I am mostly thinking in terms of the intent of the safety
mechanisms provided by these macros. (part of what they do is prevent
accidental overflow by capping at SIZE_T_MAX for example).

>>>  		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;
>>>  }
>>