sign-file: Use only the OpenSSL CMS API for signing

The USE_PKCS7 code in sign-file utilizes PKCS7_sign(), which allows signing
only with SHA-1. Since SHA-1 support for module signing has been removed,
drop the use of the OpenSSL PKCS7 API by the tool in favor of using only
the newer CMS API.

The use of the PKCS7 API is selected by the following:

 #if defined(LIBRESSL_VERSION_NUMBER) || \
 	OPENSSL_VERSION_NUMBER < 0x10000000L || \
 	defined(OPENSSL_NO_CMS)
 #define USE_PKCS7
 #endif

Looking at the individual ifdefs:

* LIBRESSL_VERSION_NUMBER: LibreSSL added the CMS API implementation from
  OpenSSL in 3.1.0, making the ifdef no longer relevant. This version was
  released on April 8, 2020.

* OPENSSL_VERSION_NUMBER < 0x10000000L: OpenSSL 1.0.0 was released on March
  29, 2010. Supporting earlier versions should no longer be necessary. The
  file Documentation/process/changes.rst already states that at least
  version 1.0.0 is required to build the kernel.

* OPENSSL_NO_CMS: OpenSSL can be configured with "no-cms" to disable CMS
  support. In this case, sign-file will no longer be usable. The CMS API
  support is now required.

In practice, since distributions now typically sign modules with SHA-2, for
which sign-file already required CMS API support, removing the USE_PKCS7
code shouldn't cause any issues.

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
[Sami: Used Petr's updated commit message]
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

Author: petrpavlu

scripts/sign-file.c

@@ -24,6 +24,7 @@
 #include <arpa/inet.h>
 #include <openssl/opensslv.h>
 #include <openssl/bio.h>
+#include <openssl/cms.h>
 #include <openssl/evp.h>
 #include <openssl/pem.h>
 #include <openssl/err.h>
@@ -39,29 +40,6 @@
 #endif
 #include "ssl-common.h"
 
-/*
- * Use CMS if we have openssl-1.0.0 or newer available - otherwise we have to
- * assume that it's not available and its header file is missing and that we
- * should use PKCS#7 instead.  Switching to the older PKCS#7 format restricts
- * the options we have on specifying the X.509 certificate we want.
- *
- * Further, older versions of OpenSSL don't support manually adding signers to
- * the PKCS#7 message so have to accept that we get a certificate included in
- * the signature message.  Nor do such older versions of OpenSSL support
- * signing with anything other than SHA1 - so we're stuck with that if such is
- * the case.
- */
-#if defined(LIBRESSL_VERSION_NUMBER) || \
-	OPENSSL_VERSION_NUMBER < 0x10000000L || \
-	defined(OPENSSL_NO_CMS)
-#define USE_PKCS7
-#endif
-#ifndef USE_PKCS7
-#include <openssl/cms.h>
-#else
-#include <openssl/pkcs7.h>
-#endif
-
 struct module_signature {
 	uint8_t		algo;		/* Public-key crypto algorithm [0] */
 	uint8_t		hash;		/* Digest algorithm [0] */
@@ -228,15 +206,10 @@ int main(int argc, char **argv)
 	bool raw_sig = false;
 	unsigned char buf[4096];
 	unsigned long module_size, sig_size;
-	unsigned int use_signed_attrs;
 	const EVP_MD *digest_algo;
 	EVP_PKEY *private_key;
-#ifndef USE_PKCS7
 	CMS_ContentInfo *cms = NULL;
 	unsigned int use_keyid = 0;
-#else
-	PKCS7 *pkcs7 = NULL;
-#endif
 	X509 *x509;
 	BIO *bd, *bm;
 	int opt, n;
@@ -246,21 +219,13 @@ int main(int argc, char **argv)
 
 	key_pass = getenv("KBUILD_SIGN_PIN");
 
-#ifndef USE_PKCS7
-	use_signed_attrs = CMS_NOATTR;
-#else
-	use_signed_attrs = PKCS7_NOATTR;
-#endif
-
 	do {
 		opt = getopt(argc, argv, "sdpk");
 		switch (opt) {
 		case 's': raw_sig = true; break;
 		case 'p': save_sig = true; break;
 		case 'd': sign_only = true; save_sig = true; break;
-#ifndef USE_PKCS7
 		case 'k': use_keyid = CMS_USE_KEYID; break;
-#endif
 		case -1: break;
 		default: format();
 		}
@@ -289,14 +254,6 @@ int main(int argc, char **argv)
 		replace_orig = true;
 	}
 
-#ifdef USE_PKCS7
-	if (strcmp(hash_algo, "sha1") != 0) {
-		fprintf(stderr, "sign-file: %s only supports SHA1 signing\n",
-			OPENSSL_VERSION_TEXT);
-		exit(3);
-	}
-#endif
-
 	/* Open the module file */
 	bm = BIO_new_file(module_name, "rb");
 	ERR(!bm, "%s", module_name);
@@ -314,7 +271,6 @@ int main(int argc, char **argv)
 		digest_algo = EVP_get_digestbyname(hash_algo);
 		ERR(!digest_algo, "EVP_get_digestbyname");
 
-#ifndef USE_PKCS7
 		/* Load the signature message from the digest buffer. */
 		cms = CMS_sign(NULL, NULL, NULL, NULL,
 			       CMS_NOCERTS | CMS_PARTIAL | CMS_BINARY |
@@ -323,19 +279,12 @@ int main(int argc, char **argv)
 
 		ERR(!CMS_add1_signer(cms, x509, private_key, digest_algo,
 				     CMS_NOCERTS | CMS_BINARY |
-				     CMS_NOSMIMECAP | use_keyid |
-				     use_signed_attrs),
+				     CMS_NOSMIMECAP | CMS_NOATTR |
+				     use_keyid),
 		    "CMS_add1_signer");
 		ERR(CMS_final(cms, bm, NULL, CMS_NOCERTS | CMS_BINARY) != 1,
 		    "CMS_final");
 
-#else
-		pkcs7 = PKCS7_sign(x509, private_key, NULL, bm,
-				   PKCS7_NOCERTS | PKCS7_BINARY |
-				   PKCS7_DETACHED | use_signed_attrs);
-		ERR(!pkcs7, "PKCS7_sign");
-#endif
-
 		if (save_sig) {
 			char *sig_file_name;
 			BIO *b;
@@ -344,13 +293,8 @@ int main(int argc, char **argv)
 			    "asprintf");
 			b = BIO_new_file(sig_file_name, "wb");
 			ERR(!b, "%s", sig_file_name);
-#ifndef USE_PKCS7
 			ERR(i2d_CMS_bio_stream(b, cms, NULL, 0) != 1,
 			    "%s", sig_file_name);
-#else
-			ERR(i2d_PKCS7_bio(b, pkcs7) != 1,
-			    "%s", sig_file_name);
-#endif
 			BIO_free(b);
 		}
 
@@ -377,11 +321,7 @@ int main(int argc, char **argv)
 	module_size = BIO_number_written(bd);
 
 	if (!raw_sig) {
-#ifndef USE_PKCS7
 		ERR(i2d_CMS_bio_stream(bd, cms, NULL, 0) != 1, "%s", dest_name);
-#else
-		ERR(i2d_PKCS7_bio(bd, pkcs7) != 1, "%s", dest_name);
-#endif
 	} else {
 		BIO *b;