If either the Subject + subjectKeyId or the Issuer + Serial number
differs between the certificate and the CA, the certificate is not
self-signed. In practice, both will be equal for self-signed
certificates and both will differ for CA-signed certificates. It is only
an issue if the CA used the same serial number for its own self-signed
certificate and the certificate we are checking. This is probably not
valid / recommended, but we should not assume that the certificate is
self-signed because of that.
Fixes: 4573b64a31cd ("X.509: Support X.509 lookup by Issuer+Serial form AuthorityKeyIdentifier")
Signed-off-by: Michal Marek <[email protected]>
---
crypto/asymmetric_keys/x509_public_key.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 7092d5cbb5d3..2c46e022a2a3 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -308,9 +308,10 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
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)) {
+ if ((!cert->akid_skid ||
+ asymmetric_key_id_same(cert->skid, cert->akid_skid)) &&
+ (!cert->akid_id ||
+ 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;
--
2.1.4
2016-02-11 21:34 GMT+08:00 Michal Marek <[email protected]>:
> If either the Subject + subjectKeyId or the Issuer + Serial number
> differs between the certificate and the CA, the certificate is not
> self-signed. In practice, both will be equal for self-signed
> certificates and both will differ for CA-signed certificates. It is only
> an issue if the CA used the same serial number for its own self-signed
> certificate and the certificate we are checking. This is probably not
> valid / recommended, but we should not assume that the certificate is
> self-signed because of that.
>
> Fixes: 4573b64a31cd ("X.509: Support X.509 lookup by Issuer+Serial form AuthorityKeyIdentifier")
> Signed-off-by: Michal Marek <[email protected]>
Tested-by: Lee, Chun-Yi <[email protected]>
Regards
Joey Lee
> ---
> crypto/asymmetric_keys/x509_public_key.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index 7092d5cbb5d3..2c46e022a2a3 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -308,9 +308,10 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
> 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)) {
> + if ((!cert->akid_skid ||
> + asymmetric_key_id_same(cert->skid, cert->akid_skid)) &&
> + (!cert->akid_id ||
> + 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;
> --
> 2.1.4
>
Hi Michal,
I have the attached patch already in my queue.
David
---
commit d19fcb825912c67e09e0575b95accaa42899e07f
Author: David Howells <[email protected]>
Date: Wed Feb 24 14:37:54 2016 +0000
X.509: Don't treat self-signed keys specially
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 <[email protected]>
Acked-by: Mimi Zohar <[email protected]>
cc: David Woodhouse <[email protected]>
diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 9e9e5a6a9ed6..fd76eca902b8 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -255,6 +255,9 @@ 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;
@@ -312,19 +315,23 @@ 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;
}
/* Propose a description */
On 2016-02-24 15:54, David Howells wrote:
> Hi Michal,
>
> I have the attached patch already in my queue.
>
> David
> ---
> commit d19fcb825912c67e09e0575b95accaa42899e07f
> Author: David Howells <[email protected]>
> Date: Wed Feb 24 14:37:54 2016 +0000
>
> X.509: Don't treat self-signed keys specially
Hi David,
this solves my problem too, obviously. I thought the signature check for
self-signed certificates was a sort of consistency check.
Thanks,
Michal