Messages in this thread Patch in this message | | | Subject | [RFC PATCH 04/20] X.509: Don't treat self-signed keys specially [ver #2] | From | David Howells <> | Date | Tue, 19 Jan 2016 11:30:56 +0000 |
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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 */
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