Re: [patch] Smack: freeing an error pointer in smk_write_revoke_subj()

[Lukasz Pawelczyk <l.pawelczyk@samsung.com>]

On czw, 2015-06-11 at 11:51 +0300, Dan Carpenter wrote:
> This code used to rely on the fact that kfree(NULL) was a no-op, but
> then we changed smk_parse_smack() to return error pointers on failure
> instead of NULL.  Calling kfree() on an error pointer will oops.
> 
> I have re-arranged things a bit so that we only free things if they
> have been allocated.
> 
> Fixes: e774ad683f42 ('smack: pass error code through pointers')
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Looks good to me.

> 
> diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
> index 6beac42..2716d02 100644
> --- a/security/smack/smackfs.c
> +++ b/security/smack/smackfs.c
> @@ -2253,8 +2253,8 @@ static const struct file_operations smk_access2_ops = {
>  static ssize_t smk_write_revoke_subj(struct file *file, const char __user *buf,
>  				size_t count, loff_t *ppos)
>  {
> -	char *data = NULL;
> -	const char *cp = NULL;
> +	char *data;
> +	const char *cp;
>  	struct smack_known *skp;
>  	struct smack_rule *sp;
>  	struct list_head *rule_list;
> @@ -2276,18 +2276,18 @@ static ssize_t smk_write_revoke_subj(struct file *file, const char __user *buf,
>  
>  	if (copy_from_user(data, buf, count) != 0) {
>  		rc = -EFAULT;
> -		goto free_out;
> +		goto out_data;
>  	}
>  
>  	cp = smk_parse_smack(data, count);
>  	if (IS_ERR(cp)) {
>  		rc = PTR_ERR(cp);
> -		goto free_out;
> +		goto out_data;
>  	}
>  
>  	skp = smk_find_entry(cp);
>  	if (skp = NULL)
> -		goto free_out;
> +		goto out_cp;
>  
>  	rule_list = &skp->smk_rules;
>  	rule_lock = &skp->smk_rules_lock;
> @@ -2299,9 +2299,11 @@ static ssize_t smk_write_revoke_subj(struct file *file, const char __user *buf,
>  
>  	mutex_unlock(rule_lock);
>  
> -free_out:
> -	kfree(data);
> +out_cp:
>  	kfree(cp);
> +out_data:
> +	kfree(data);
> +
>  	return rc;
>  }
>  
> --
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-- 
Lukasz Pawelczyk
Samsung R&D Institute Poland
Samsung Electronics