linux-kernel - Re: [PATCH] coccinelle: api: add kzfree script

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Message-ID: <345c783b-a8cf-9dd1-29c6-d32b9b29053f@linux.com>
Date:   Sun, 14 Jun 2020 22:42:54 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Joe Perches <joe@...ches.com>, Julia Lawall <Julia.Lawall@...6.fr>,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     cocci@...teme.lip6.fr, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coccinelle: api: add kzfree script

On 6/4/20 7:27 PM, Joe Perches wrote:
> On Thu, 2020-06-04 at 17:08 +0300, Denis Efremov wrote:
>> Check for memset() with 0 followed by kfree().
> 
> Perhaps those uses should be memzero_explicit or kvfree_sensitive.
> 

Is it safe to suggest to use kzfree instead of memzero_explicit && kfree?
Or it would be better to use kvfree_sensitive in this case.

kzfree uses memset(0) with no barrier_data.

For example:
diff -u -p a/drivers/crypto/inside-secure/safexcel_hash.c b/drivers/crypto/inside-secure/safexcel_hash.c
--- a/drivers/crypto/inside-secure/safexcel_hash.c
+++ b/drivers/crypto/inside-secure/safexcel_hash.c
@@ -1081,8 +1081,7 @@ static int safexcel_hmac_init_pad(struct
                }
 
                /* Avoid leaking */
-               memzero_explicit(keydup, keylen);
-               kfree(keydup);
+               kzfree(keydup);
 
                if (ret)
                        return ret;

Thanks,
Denis