Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1312145 > unrolled thread

[RFC PATCH 04/20] X.509: Don't treat self-signed keys specially [ver #2]

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [RFC PATCH 04/20] X.509: Don't treat self-signed keys specially  [ver #2] David Howells <dhowells@redhat.com> - 2016-01-19 12:40 +0100
    Re: [RFC PATCH 04/20] X.509: Don't treat self-signed keys specially  [ver #2] Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-01-20 21:50 +0100

#1312145 — [RFC PATCH 04/20] X.509: Don't treat self-signed keys specially [ver #2]

Trust for a self-signed certificate can normally only be determined by
whether we obtained it from a trusted location (ie. it was built into the
kernel at compile time), so there's not really any point in checking it -
we could verify that the signature is valid, but it doesn't really tell us
anything if the signature checks out.

However, there's a bug in the code determining whether a certificate is
self-signed or not - if they have neither AKID nor SKID then we just assume
that the cert is self-signed, which may not be true.

Given this, remove the code that treats self-signed certs specially when it
comes to evaluating trustability and attempt to evaluate them as ordinary
signed certificates.  We then expect self-signed certificates to fail the
trustability check and be marked as untrustworthy in x509_key_preparse().

Note that there is the possibility of the trustability check on a
self-signed cert then succeeding.  This is most likely to happen when a
duplicate of the certificate is already on the trust keyring - in which
case it shouldn't be a problem.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: David Woodhouse <David.Woodhouse@intel.com>
cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
---

 crypto/asymmetric_keys/x509_public_key.c |   25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index c4f3c40a4ab9..630c1c331fe1 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -265,6 +265,9 @@ static int x509_validate_trust(struct x509_certificate *cert,
 	struct key *key;
 	int ret = 1;
 
+	if (!cert->akid_id && !cert->akid_skid)
+		return 1;
+
 	if (!trust_keyring)
 		return -EOPNOTSUPP;
 
@@ -322,19 +325,23 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 	cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
 	cert->pub->id_type = PKEY_ID_X509;
 
-	/* Check the signature on the key if it appears to be self-signed */
-	if ((!cert->akid_skid && !cert->akid_id) ||
-	    asymmetric_key_id_same(cert->skid, cert->akid_skid) ||
-	    asymmetric_key_id_same(cert->id, cert->akid_id)) {
-		ret = x509_check_signature(cert->pub, cert); /* self-signed */
-		if (ret < 0)
-			goto error_free_cert;
-	} else if (!prep->trusted) {
+	/* See if we can derive the trustability of this certificate.
+	 *
+	 * When it comes to self-signed certificates, we cannot evaluate
+	 * trustedness except by the fact that we obtained it from a trusted
+	 * location.  So we just rely on x509_validate_trust() failing in this
+	 * case.
+	 *
+	 * Note that there's a possibility of a self-signed cert matching a
+	 * cert that we have (most likely a duplicate that we already trust) -
+	 * in which case it will be marked trusted.
+	 */
+	if (!prep->trusted) {
 		ret = x509_validate_trust(cert, get_system_trusted_keyring());
 		if (ret)
 			ret = x509_validate_trust(cert, get_ima_mok_keyring());
 		if (!ret)
-			prep->trusted = 1;
+			prep->trusted = true;
 	}
 
 	/* Don't permit addition of blacklisted keys */

[toc] | [next] | [standalone]

#1313520

On Tue, 2016-01-19 at 11:30 +0000, David Howells wrote:
> Trust for a self-signed certificate can normally only be determined by
> whether we obtained it from a trusted location (ie. it was built into the
> kernel at compile time), so there's not really any point in checking it -
> we could verify that the signature is valid, but it doesn't really tell us
> anything if the signature checks out.
> 
> However, there's a bug in the code determining whether a certificate is
> self-signed or not - if they have neither AKID nor SKID then we just assume
> that the cert is self-signed, which may not be true.
> 
> Given this, remove the code that treats self-signed certs specially when it
> comes to evaluating trustability and attempt to evaluate them as ordinary
> signed certificates.  We then expect self-signed certificates to fail the
> trustability check and be marked as untrustworthy in x509_key_preparse().
> 
> Note that there is the possibility of the trustability check on a
> self-signed cert then succeeding.  This is most likely to happen when a
> duplicate of the certificate is already on the trust keyring - in which
> case it shouldn't be a problem.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: David Woodhouse <David.Woodhouse@intel.com>
> cc: Mimi Zohar <zohar@linux.vnet.ibm.com>

Acked-by:  Mimi Zohar <zohar@linux.vnet.ibm.com

> ---
> 
>  crypto/asymmetric_keys/x509_public_key.c |   25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index c4f3c40a4ab9..630c1c331fe1 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -265,6 +265,9 @@ static int x509_validate_trust(struct x509_certificate *cert,
>  	struct key *key;
>  	int ret = 1;
> 
> +	if (!cert->akid_id && !cert->akid_skid)
> +		return 1;
> +
>  	if (!trust_keyring)
>  		return -EOPNOTSUPP;
> 
> @@ -322,19 +325,23 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
>  	cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
>  	cert->pub->id_type = PKEY_ID_X509;
> 
> -	/* Check the signature on the key if it appears to be self-signed */
> -	if ((!cert->akid_skid && !cert->akid_id) ||
> -	    asymmetric_key_id_same(cert->skid, cert->akid_skid) ||
> -	    asymmetric_key_id_same(cert->id, cert->akid_id)) {
> -		ret = x509_check_signature(cert->pub, cert); /* self-signed */
> -		if (ret < 0)
> -			goto error_free_cert;
> -	} else if (!prep->trusted) {
> +	/* See if we can derive the trustability of this certificate.
> +	 *
> +	 * When it comes to self-signed certificates, we cannot evaluate
> +	 * trustedness except by the fact that we obtained it from a trusted
> +	 * location.  So we just rely on x509_validate_trust() failing in this
> +	 * case.
> +	 *
> +	 * Note that there's a possibility of a self-signed cert matching a
> +	 * cert that we have (most likely a duplicate that we already trust) -
> +	 * in which case it will be marked trusted.
> +	 */
> +	if (!prep->trusted) {
>  		ret = x509_validate_trust(cert, get_system_trusted_keyring());
>  		if (ret)
>  			ret = x509_validate_trust(cert, get_ima_mok_keyring());
>  		if (!ret)
> -			prep->trusted = 1;
> +			prep->trusted = true;
>  	}
> 
>  	/* Don't permit addition of blacklisted keys */
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web