PKCS#7: Check content type and versions

We only support PKCS#7 signed-data [RFC2315 sec 9] content at the top level,
so reject anything else.  Further, check that the version numbers in
SignedData and SignerInfo are 1 in both cases.

Note that we don't restrict the inner content type.  In the PKCS#7 code we
don't parse the data attached there, but merely verify the signature over
it.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-By: David Woodhouse <David.Woodhouse@intel.com>

crypto/asymmetric_keys/pkcs7.asn1

@@ -1,12 +1,12 @@
 PKCS7ContentInfo ::= SEQUENCE {
-	contentType	ContentType,
+	contentType	ContentType ({ pkcs7_check_content_type }),
 	content		[0] EXPLICIT SignedData OPTIONAL
 }
 
 ContentType ::= OBJECT IDENTIFIER ({ pkcs7_note_OID })
 
 SignedData ::= SEQUENCE {
-	version			INTEGER,
+	version			INTEGER ({ pkcs7_note_signeddata_version }),
 	digestAlgorithms	DigestAlgorithmIdentifiers,
 	contentInfo		ContentInfo,
 	certificates		CHOICE {
@@ -68,7 +68,7 @@ SignerInfos ::= CHOICE {
 }
 
 SignerInfo ::= SEQUENCE {
-	version			INTEGER,
+	version			INTEGER ({ pkcs7_note_signerinfo_version }),
 	issuerAndSerialNumber	IssuerAndSerialNumber,
 	digestAlgorithm		DigestAlgorithmIdentifier ({ pkcs7_sig_note_digest_algo }),
 	authenticatedAttributes	CHOICE {

crypto/asymmetric_keys/pkcs7_parser.c

@@ -225,6 +225,79 @@ int pkcs7_sig_note_pkey_algo(void *context, size_t hdrlen,
 	return 0;
 }
 
+/*
+ * We only support signed data [RFC2315 sec 9].
+ */
+int pkcs7_check_content_type(void *context, size_t hdrlen,
+			     unsigned char tag,
+			     const void *value, size_t vlen)
+{
+	struct pkcs7_parse_context *ctx = context;
+
+	if (ctx->last_oid != OID_signed_data) {
+		pr_warn("Only support pkcs7_signedData type\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Note the SignedData version
+ */
+int pkcs7_note_signeddata_version(void *context, size_t hdrlen,
+				  unsigned char tag,
+				  const void *value, size_t vlen)
+{
+	unsigned version;
+
+	if (vlen != 1)
+		goto unsupported;
+
+	version = *(const u8 *)value;
+	switch (version) {
+	case 1:
+		/* PKCS#7 SignedData [RFC2315 sec 9.1] */
+		break;
+	default:
+		goto unsupported;
+	}
+
+	return 0;
+
+unsupported:
+	pr_warn("Unsupported SignedData version\n");
+	return -EINVAL;
+}
+
+/*
+ * Note the SignerInfo version
+ */
+int pkcs7_note_signerinfo_version(void *context, size_t hdrlen,
+				  unsigned char tag,
+				  const void *value, size_t vlen)
+{
+	unsigned version;
+
+	if (vlen != 1)
+		goto unsupported;
+
+	version = *(const u8 *)value;
+	switch (version) {
+	case 1:
+		/* PKCS#7 SignerInfo [RFC2315 sec 9.2] */
+		break;
+	default:
+		goto unsupported;
+	}
+
+	return 0;
+
+unsupported:
+	pr_warn("Unsupported SignerInfo version\n");
+	return -EINVAL;
+}
+
 /*
  * Extract a certificate and store it in the context.
  */
@@ -326,7 +399,7 @@ int pkcs7_sig_note_authenticated_attr(void *context, size_t hdrlen,
 }
 
 /*
- * Note the set of auth attributes for digestion purposes [RFC2315 9.3]
+ * Note the set of auth attributes for digestion purposes [RFC2315 sec 9.3]
  */
 int pkcs7_sig_note_set_of_authattrs(void *context, size_t hdrlen,
 				    unsigned char tag,