[PATCH v2 6/8] lib: crypto: export and enhance pkcs7_verify_one()

[AKASHI Takahiro]

The function, pkcs7_verify_one(), will be utilized to rework signature
verification logic aiming to support intermediate certificates in
"chain of trust."

To do that, its function interface is expanded, adding an extra argument
which is expected to return the last certificate in trusted chain.
Then, this last one must further be verified with signature database, db
and/or dbx.

Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
---
 include/crypto/pkcs7.h    |  9 +++++-
 lib/crypto/pkcs7_verify.c | 61 ++++++++++++++++++++++++++++++++++-----
 2 files changed, 62 insertions(+), 8 deletions(-)

diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
index 8f5c8a7ee3b9..ca35df29f6fb 100644
--- a/include/crypto/pkcs7.h
+++ b/include/crypto/pkcs7.h
@@ -27,7 +27,14 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
 				  const void **_data, size_t *_datalen,
 				  size_t *_headerlen);
 
-#ifndef __UBOOT__
+#ifdef __UBOOT__
+struct pkcs7_signed_info;
+struct x509_certificate;
+
+int pkcs7_verify_one(struct pkcs7_message *pkcs7,
+		     struct pkcs7_signed_info *sinfo,
+		     struct x509_certificate **signer);
+#else
 /*
  * pkcs7_trust.c
  */
diff --git a/lib/crypto/pkcs7_verify.c b/lib/crypto/pkcs7_verify.c
index 9b9030ea4440..dda96ccf57a2 100644
--- a/lib/crypto/pkcs7_verify.c
+++ b/lib/crypto/pkcs7_verify.c
@@ -302,10 +302,27 @@ static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 }
 
 /*
- * Verify the internal certificate chain as best we can.
+ * pkcs7_verify_sig_chain - Verify the internal certificate chain as best
+ *                          as we can.
+ * @pkcs7:	PKCS7 Signed Data
+ * @sinfo:	PKCS7 Signed Info
+ * @signer:	Singer's certificate
+ *
+ * Build up and verify the internal certificate chain against a signature
+ * in @sinfo, using certificates contained in @pkcs7 as best as we can.
+ * If the chain reaches the end, the last certificate will be returned
+ * in @signer.
+ *
+ * Return:	0 - on success, non-zero error code - otherwise
  */
+#ifdef __UBOOT__
+static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
+				  struct pkcs7_signed_info *sinfo,
+				  struct x509_certificate **signer)
+#else
 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 				  struct pkcs7_signed_info *sinfo)
+#endif
 {
 	struct public_key_signature *sig;
 	struct x509_certificate *x509 = sinfo->signer, *p;
@@ -314,6 +331,8 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 
 	kenter("");
 
+	*signer = NULL;
+
 	for (p = pkcs7->certs; p; p = p->next)
 		p->seen = false;
 
@@ -331,6 +350,9 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 			for (p = sinfo->signer; p != x509; p = p->signer)
 				p->blacklisted = true;
 			pr_debug("- blacklisted\n");
+#ifdef __UBOOT__
+			*signer = x509;
+#endif
 			return 0;
 		}
 
@@ -356,6 +378,9 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 				goto unsupported_crypto_in_x509;
 			x509->signer = x509;
 			pr_debug("- self-signed\n");
+#ifdef __UBOOT__
+			*signer = x509;
+#endif
 			return 0;
 		}
 
@@ -386,6 +411,9 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 
 		/* We didn't find the root of this chain */
 		pr_debug("- top\n");
+#ifdef __UBOOT__
+		*signer = x509;
+#endif
 		return 0;
 
 	found_issuer_check_skid:
@@ -403,6 +431,9 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 		if (p->seen) {
 			pr_warn("Sig %u: X.509 chain contains loop\n",
 				sinfo->index);
+#ifdef __UBOOT__
+			*signer = p;
+#endif
 			return 0;
 		}
 		ret = public_key_verify_signature(p->pub, x509->sig);
@@ -411,6 +442,9 @@ static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 		x509->signer = p;
 		if (x509 == p) {
 			pr_debug("- self-signed\n");
+#ifdef __UBOOT__
+			*signer = p;
+#endif
 			return 0;
 		}
 		x509 = p;
@@ -430,13 +464,26 @@ unsupported_crypto_in_x509:
 }
 
 /*
- * Verify one signed information block from a PKCS#7 message.
+ * pkcs7_verify_one - Verify one signed information block from a PKCS#7
+ *                    message.
+ * @pkcs7:	PKCS7 Signed Data
+ * @sinfo:	PKCS7 Signed Info
+ * @signer:	Signer's certificate
+ *
+ * Verify one signature in @sinfo and follow the certificate chain.
+ * If the chain reaches the end, the last certificate will be returned
+ * in @signer.
+ *
+ * Return:	0 - on success, non-zero error code - otherwise
  */
-#ifndef __UBOOT__
-static
-#endif
+#ifdef __UBOOT__
 int pkcs7_verify_one(struct pkcs7_message *pkcs7,
-		     struct pkcs7_signed_info *sinfo)
+		     struct pkcs7_signed_info *sinfo,
+		     struct x509_certificate **signer)
+#else
+static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
+			    struct pkcs7_signed_info *sinfo)
+#endif
 {
 	int ret;
 
@@ -480,7 +527,7 @@ int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 	pr_devel("Verified signature %u\n", sinfo->index);
 
 	/* Verify the internal certificate chain */
-	return pkcs7_verify_sig_chain(pkcs7, sinfo);
+	return pkcs7_verify_sig_chain(pkcs7, sinfo, signer);
 }
 
 #ifndef __UBOOT__
-- 
2.27.0