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

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Message-ID: <aRsfBDC3Y8OHOnOl@stanley.mountain>
Date: Mon, 17 Nov 2025 16:11:32 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Ally Heev <allyheev@...il.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Aleksandr Loktionov <aleksandr.loktionov@...el.com>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH v3] net: ethernet: fix uninitialized
 pointers with free attribute

On Thu, Nov 06, 2025 at 03:07:26PM +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`.
> 
> Variable declarations must be in one block and sorted from the longest
> to the shortest.
> 

These days, with __free the trend is to say yes this is RAII and we
should declare it where you use it.  I personally don't have a strong
opinion on this either way, but other maintainers do and will NAK the
`= NULL` approach.

The documentation says you should do it that way and avoid the `= NULL`
as well.  The issue is with lock ordering.  It's a FILO ordering, so if
we require a specific unlock order then declaring variables at the top
could mess things up.

The counter argument is that if you declare a variable after a goto
then that's undefined behavior as well.  Clang will detect that bug so
it be detected before it hits actual users.

regards,
dan carpenter