X.509: Extract signature digest and make self-signed cert checks earlier

Extract the signature digest for an X.509 certificate earlier, at the end
of x509_cert_parse() rather than leaving it to the callers thereof since it
has to be called anyway.

Further, immediately after that, check the signature on self-signed
certificates, also rather in the callers of x509_cert_parse().

We note in the x509_certificate struct the following bits of information:

 (1) Whether the signature is self-signed (even if we can't check the
     signature due to missing crypto).

 (2) Whether the key held in the certificate needs unsupported crypto to be
     used.  We may get a PKCS#7 message with X.509 certs that we can't make
     use of - we just ignore them and give ENOPKG at the end it we couldn't
     verify anything if at least one of these unusable certs are in the
     chain of trust.

 (3) Whether the signature held in the certificate needs unsupported crypto
     to be checked.  We can still use the key held in this certificate,
     even if we can't check the signature on it - if it is held in the
     system trusted keyring, for instance.  We just can't add it to a ring
     of trusted keys or follow it further up the chain of trust.

Making these checks earlier allows x509_check_signature() to be removed and
replaced with direct calls to public_key_verify_signature().

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 10 insertions, 28 deletions

diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
index 1426f03e630b..44b746e9df1b 100644
--- a/crypto/asymmetric_keys/pkcs7_verify.c
+++ b/crypto/asymmetric_keys/pkcs7_verify.c
@@ -190,9 +190,8 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 			 x509->subject,
 			 x509->raw_serial_size, x509->raw_serial);
 		x509->seen = true;
-		ret = x509_get_sig_params(x509);
-		if (ret < 0)
-			goto maybe_missing_crypto_in_x509;
+		if (x509->unsupported_key)
+			goto unsupported_crypto_in_x509;
 
 		pr_debug("- issuer %s\n", x509->issuer);
 		sig = x509->sig;
@@ -203,22 +202,14 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 			pr_debug("- authkeyid.skid %*phN\n",
 				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
 
-		if ((!x509->sig->auth_ids[0] && !x509->sig->auth_ids[1]) ||
-		    strcmp(x509->subject, x509->issuer) == 0) {
+		if (x509->self_signed) {
 			/* If there's no authority certificate specified, then
 			 * the certificate must be self-signed and is the root
 			 * of the chain.  Likewise if the cert is its own
 			 * authority.
 			 */
-			pr_debug("- no auth?\n");
-			if (x509->raw_subject_size != x509->raw_issuer_size ||
-			    memcmp(x509->raw_subject, x509->raw_issuer,
-				   x509->raw_issuer_size) != 0)
-				return 0;
-
-			ret = x509_check_signature(x509->pub, x509);
-			if (ret < 0)
-				goto maybe_missing_crypto_in_x509;
+			if (x509->unsupported_sig)
+				goto unsupported_crypto_in_x509;
 			x509->signer = x509;
 			pr_debug("- self-signed\n");
 			return 0;
@@ -270,7 +261,7 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 				sinfo->index);
 			return 0;
 		}
-		ret = x509_check_signature(p->pub, x509);
+		ret = public_key_verify_signature(p->pub, p->sig);
 		if (ret < 0)
 			return ret;
 		x509->signer = p;
@@ -282,16 +273,14 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 		might_sleep();
 	}
 
-maybe_missing_crypto_in_x509:
+unsupported_crypto_in_x509:
 	/* Just prune the certificate chain at this point if we lack some
 	 * crypto module to go further.  Note, however, we don't want to set
-	 * sinfo->missing_crypto as the signed info block may still be
+	 * sinfo->unsupported_crypto as the signed info block may still be
 	 * validatable against an X.509 cert lower in the chain that we have a
 	 * trusted copy of.
 	 */
-	if (ret == -ENOPKG)
-		return 0;
-	return ret;
+	return 0;
 }
 
 /*
@@ -378,9 +367,8 @@ int pkcs7_verify(struct pkcs7_message *pkcs7,
 		 enum key_being_used_for usage)
 {
 	struct pkcs7_signed_info *sinfo;
-	struct x509_certificate *x509;
 	int enopkg = -ENOPKG;
-	int ret, n;
+	int ret;
 
 	kenter("");
 
@@ -422,12 +410,6 @@ int pkcs7_verify(struct pkcs7_message *pkcs7,
 		return -EINVAL;
 	}
 
-	for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
-		ret = x509_get_sig_params(x509);
-		if (ret < 0)
-			return ret;
-	}
-
 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 		ret = pkcs7_verify_one(pkcs7, sinfo);
 		if (ret < 0) {