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

Lukasz Pawelczyk
2015-06-11T09:11:59Z

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