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

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Message-ID: <afa219b7-9ce3-4da8-a339-8f363d77824e@intel.com>
Date: Fri, 7 Nov 2025 06:39:49 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: ally heev <allyheev@...il.com>, Alexander Lobakin
	<aleksander.lobakin@...el.com>
CC: Tony Nguyen <anthony.l.nguyen@...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>, Dan Carpenter
	<dan.carpenter@...aro.org>
Subject: Re: [Intel-wired-lan] [PATCH v3] net: ethernet: fix uninitialized
 pointers with free attribute

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