linux-kernel - Re: [PATCH net v2] net: wireless: Use kfree

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Message-ID: <2023072020-epilepsy-duchess-0a80@gregkh>
Date:   Thu, 20 Jul 2023 15:25:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@....cz>
Cc:     王明-软件底层技术部 
        <machel@...o.com>, Ajay Singh <ajay.kathat@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Kalle Valo <kvalo@...nel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "opensource.kernel" <opensource.kernel@...o.com>
Subject: Re: [PATCH net v2] net: wireless: Use kfree_sensitive instead of
 kfree

On Thu, Jul 20, 2023 at 11:06:36AM +0200, Pavel Machek wrote:
> Hi!
> 
> > > diff --git a/drivers/net/wireless/microchip/wilc1000/cfg80211.c b/drivers/net/wireless/microchip/wilc1000/cfg80211.c
> > > index b545d93c6e37..45bcadeba2da 100644
> > > --- a/drivers/net/wireless/microchip/wilc1000/cfg80211.c
> > > +++ b/drivers/net/wireless/microchip/wilc1000/cfg80211.c
> > > @@ -518,7 +518,7 @@ static int wilc_wfi_cfg_allocate_wpa_igtk_entry(struct wilc_priv *priv, u8 idx)
> > >  static int wilc_wfi_cfg_copy_wpa_info(struct wilc_wfi_key *key_info,
> > >  				      struct key_params *params)
> > >  {
> > > -	kfree(key_info->key);
> > > +	kfree_sensitive(key_info->key);
> > >  
> > >  	key_info->key = kmemdup(params->key, params->key_len, GFP_KERNEL);
> > >  	if (!key_info->key)
> > > @@ -656,7 +656,7 @@ static int del_key(struct wiphy *wiphy, struct net_device *netdev, int link_id,
> > >  	if (!pairwise && (key_index == 4 || key_index == 5)) {
> > >  		key_index -= 4;
> > >  		if (priv->wilc_igtk[key_index]) {
> > > -			kfree(priv->wilc_igtk[key_index]->key);
> > > +			kfree_sensitive(priv->wilc_igtk[key_index]->key);
> > 
> > Normally "kfree_sensitive()" is used at the end of a function for when
> > kfree() of a local variable might not be called because the compiler
> > thinks it is smarter than us and optimizes it away.
> > 
> > Putting it here, in the normal operation, really doesn't do anything,
> > right?  There's always going to be odd data in the heap and normal
> 
> It does memzero.
> 
> https://elixir.bootlin.com/linux/latest/source/mm/slab_common.c#L1411

I know what it does, I'm saying "why is this required".