linux-kernel - Re: [net-next PATCH 3/9] octeontx2-pf: Create representor netdev

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Date: Wed, 17 Apr 2024 18:36:47 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: oe-kbuild@...ts.linux.dev, Geetha sowjanya <gakula@...vell.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: lkp@...el.com, oe-kbuild-all@...ts.linux.dev, kuba@...nel.org,
	davem@...emloft.net, pabeni@...hat.com, edumazet@...gle.com,
	sgoutham@...vell.com, sbhatta@...vell.com, hkelam@...vell.com
Subject: Re: [net-next PATCH 3/9] octeontx2-pf: Create representor netdev

On Wed, Apr 17, 2024 at 06:24:13PM +0300, Dan Carpenter wrote:
> f9a5b510759eeb Geetha sowjanya 2024-04-16  132  int rvu_rep_create(struct otx2_nic *priv)
> f9a5b510759eeb Geetha sowjanya 2024-04-16  133  {
> f9a5b510759eeb Geetha sowjanya 2024-04-16  134  	int rep_cnt = priv->rep_cnt;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  135  	struct net_device *ndev;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  136  	struct rep_dev *rep;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  137  	int rep_id, err;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  138  	u16 pcifunc;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  139  
> f9a5b510759eeb Geetha sowjanya 2024-04-16  140  	priv->reps = devm_kcalloc(priv->dev, rep_cnt, sizeof(struct rep_dev), GFP_KERNEL);
> f9a5b510759eeb Geetha sowjanya 2024-04-16  141  	if (!priv->reps)
> f9a5b510759eeb Geetha sowjanya 2024-04-16  142  		return -ENOMEM;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  143  
> f9a5b510759eeb Geetha sowjanya 2024-04-16  144  	for (rep_id = 0; rep_id < rep_cnt; rep_id++) {
> f9a5b510759eeb Geetha sowjanya 2024-04-16  145  		ndev = alloc_etherdev(sizeof(*rep));
> f9a5b510759eeb Geetha sowjanya 2024-04-16  146  		if (!ndev) {
> f9a5b510759eeb Geetha sowjanya 2024-04-16  147  			dev_err(priv->dev, "PFVF representor:%d creation failed\n", rep_id);
> f9a5b510759eeb Geetha sowjanya 2024-04-16  148  			err = -ENOMEM;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  149  			goto exit;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  150  		}
> f9a5b510759eeb Geetha sowjanya 2024-04-16  151  
> f9a5b510759eeb Geetha sowjanya 2024-04-16  152  		rep = netdev_priv(ndev);
> f9a5b510759eeb Geetha sowjanya 2024-04-16  153  		priv->reps[rep_id] = rep;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  154  		rep->mdev = priv;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  155  		rep->netdev = ndev;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  156  		rep->rep_id = rep_id;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  157  
> f9a5b510759eeb Geetha sowjanya 2024-04-16  158  		ndev->min_mtu = OTX2_MIN_MTU;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  159  		ndev->max_mtu = priv->hw.max_mtu;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  160  		pcifunc = priv->rep_pf_map[rep_id];
> f9a5b510759eeb Geetha sowjanya 2024-04-16  161  		rep->pcifunc = pcifunc;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  162  
> f9a5b510759eeb Geetha sowjanya 2024-04-16  163  		snprintf(ndev->name, sizeof(ndev->name), "r%dp%dv%d", rep_id,
> f9a5b510759eeb Geetha sowjanya 2024-04-16  164  			 rvu_get_pf(pcifunc), (pcifunc & RVU_PFVF_FUNC_MASK));
> f9a5b510759eeb Geetha sowjanya 2024-04-16  165  
> f9a5b510759eeb Geetha sowjanya 2024-04-16  166  		eth_hw_addr_random(ndev);
> f9a5b510759eeb Geetha sowjanya 2024-04-16  167  		if (register_netdev(ndev)) {
> 
> err = register_netdev(ndev);
> if (err) {
> 
> f9a5b510759eeb Geetha sowjanya 2024-04-16  168  			dev_err(priv->dev, "PFVF reprentator registration failed\n");
> f9a5b510759eeb Geetha sowjanya 2024-04-16  169  			free_netdev(ndev);
>                                                                                     ^^^^
> freed
> 
> f9a5b510759eeb Geetha sowjanya 2024-04-16 @170  			ndev->netdev_ops = NULL;
>                                                                         ^^^^^^^^^^^^^^^^^^^^^^^
> Use after free
> 
> f9a5b510759eeb Geetha sowjanya 2024-04-16  171  			goto exit;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  172  		}
> f9a5b510759eeb Geetha sowjanya 2024-04-16  173  	}
> f9a5b510759eeb Geetha sowjanya 2024-04-16  174  	err = rvu_rep_napi_init(priv);
> f9a5b510759eeb Geetha sowjanya 2024-04-16  175  	if (err)
> f9a5b510759eeb Geetha sowjanya 2024-04-16  176  		goto exit;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  177  
> f9a5b510759eeb Geetha sowjanya 2024-04-16  178  	return 0;
> f9a5b510759eeb Geetha sowjanya 2024-04-16  179  exit:
> f9a5b510759eeb Geetha sowjanya 2024-04-16  180  	rvu_rep_free_netdev(priv);
> 
> rvu_rep_free_netdev() also calls free_netdev() so it's a double free.

Actually the rep->netdev->netdev_ops check in rvu_rep_free_netdev() was
supposed to prevent the double free.  But since rep->netdev is already
freed, then it's another use after free.  You could use a different flag
instead of rep->netdev->netdev_ops to mean "don't free this".  But
really, it's just better to write it how I have suggested.

My patch adds some duplicate code but when you remove the conditions in
rvu_rep_free_netdev() and the "ndev->netdev_ops = NULL" assignment, then
overall it's fewer lines of code this way.

https://staticthinking.wordpress.com/2022/04/28/free-the-last-thing-style/

regards,
dan carpenter