Re: [Intel-wired-lan] [PATCH v3] net: ethernet: fix uninitialized pointers with free attribute

[ally heev <allyheev@gmail.com>]

On Fri, 2025-11-07 at 06:39 +0100, Przemek Kitszel wrote:
> On 11/6/25 17:05, ally heev wrote:
> > On Thu, 2025-11-06 at 15:07 +0100, Alexander Lobakin wrote:
> > [..]
> > > > 
> > > > diff --git a/drivers/net/ethernet/intel/ice/ice_flow.c b/drivers/net/ethernet/intel/ice/ice_flow.c
> > > > index 6d5c939dc8a515c252cd2b77d155b69fa264ee92..3590dacf3ee57879b3809d715e40bb290e40c4aa 100644
> > > > --- a/drivers/net/ethernet/intel/ice/ice_flow.c
> > > > +++ b/drivers/net/ethernet/intel/ice/ice_flow.c
> > > > @@ -1573,12 +1573,13 @@ ice_flow_set_parser_prof(struct ice_hw *hw, u16 dest_vsi, u16 fdir_vsi,
> > > >   			 struct ice_parser_profile *prof, enum ice_block blk)
> > > >   {
> > > >   	u64 id = find_first_bit(prof->ptypes, ICE_FLOW_PTYPE_MAX);
> > > > -	struct ice_flow_prof_params *params __free(kfree);
> > > >   	u8 fv_words = hw->blk[blk].es.fvw;
> > > >   	int status;
> > > >   	int i, idx;
> > > >   
> > > > -	params = kzalloc(sizeof(*params), GFP_KERNEL);
> > > > +	struct ice_flow_prof_params *params __free(kfree) =
> > > > +		kzalloc(sizeof(*params), GFP_KERNEL);
> > > 
> > > Please don't do it that way. It's not C++ with RAII and
> > > declare-where-you-use.
> > > Just leave the variable declarations where they are, but initialize them
> > > with `= NULL`.
> 
> +1
> 
> > > 
> > > Variable declarations must be in one block and sorted from the longest
> > > to the shortest.
> > > 
> > > But most important, I'm not even sure how you could trigger an
> > > "undefined behaviour" here. Both here and below the variable tagged with
> > > `__free` is initialized right after the declaration block, before any
> > > return. So how to trigger an UB here?
> > 
> > It doesn't occur here. But, many maintainers/developers consider it a
> > bad practice because if the function returns before initialization or
> > use of `goto` can cause such behaviors.
> 
> we were bitten by that already, scenario is as follow:
> 0. have a good code w/o UB and w/o redundant = NULL
> 1. add some early return, say:
> 	if (dest_vsi == fdir_vsi)
> 		return -EINVAL;
> 2. almost granted that person adding 1. will forget to add = NULL to all
> declarations marked __free
> 
> > 
> > Here though, the definitions are still at the top right? Maybe I could
> > just sort them
> 
> we discourage putting any operations, including allocations, that may
> fail into the declarations block
> 

Makes sense. I will just initialize them with NULL then