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

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Message-ID: <aQ9xp9pchMwml30P@horms.kernel.org>
Date: Sat, 8 Nov 2025 16:36:55 +0000
From: Simon Horman <horms@...nel.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,
	Dan Carpenter <dan.carpenter@...aro.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:
> From: Ally Heev <allyheev@...il.com>
> Date: Thu, 06 Nov 2025 17:25:48 +0530
> 
> > Uninitialized pointers with `__free` attribute can cause undefined
> > behavior as the memory assigned randomly to the pointer is freed
> > automatically when the pointer goes out of scope.
> > 
> > It is better to initialize and assign pointers with `__free`
> > attribute in one statement to ensure proper scope-based cleanup.
> > 
> > Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > Closes: https://lore.kernel.org/all/aPiG_F5EBQUjZqsl@stanley.mountain/
> > Signed-off-by: Ally Heev <allyheev@...il.com>
> > ---
> > Changes in v3:
> > - fixed style issues
> > - Link to v2: https://lore.kernel.org/r/20251106-aheev-uninitialized-free-attr-net-ethernet-v2-1-048da0c5d6b6@gmail.com
> > 
> > Changes in v2:
> > - fixed non-pointer initialization to NULL
> > - NOTE: drop v1
> > - Link to v1: https://lore.kernel.org/r/20251105-aheev-uninitialized-free-attr-net-ethernet-v1-1-f6ea84bbd750@gmail.com
> > ---
> >  drivers/net/ethernet/intel/ice/ice_flow.c       | 5 +++--
> >  drivers/net/ethernet/intel/idpf/idpf_virtchnl.c | 5 +++--
> >  2 files changed, 6 insertions(+), 4 deletions(-)
> > 
> > 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.
> 
> 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?

FWIIW, I'd prefer if we sidestepped this discussion entirely
by not using __free [1] in this driver.

It seems to me that for both functions updated by this
patch that can easily be achieved using an idiomatic
goto label to free on error.

[1] https://docs.kernel.org/process/maintainer-netdev.html#using-device-managed-and-cleanup-h-constructs

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