[PATCH 01/18] X.509: Parse RSASSA-PSS style certificates

[Varad Gautam]

An X.509 wrapper for a RSASSA-PSS signature contains additional
signature parameters over the PKCSv.15 encoding scheme. Extend the
x509 parser to allow parsing RSASSA-PSS encoded certificates, with
the defaults taken from RFC8017.

A certificate is rejected if the hash function used for the MGF is
different from the hash function used for signature generation,
although this is allowed in RFC8017.

References: https://tools.ietf.org/html/rfc8017#appendix-C
Signed-off-by: Varad Gautam <varad.gautam@xxxxxxxx>
---
 crypto/asymmetric_keys/Makefile           |   5 +-
 crypto/asymmetric_keys/x509_cert_parser.c | 152 ++++++++++++++++++++++
 crypto/asymmetric_keys/x509_rsassa.asn1   |  17 +++
 include/crypto/public_key.h               |   4 +
 include/linux/oid_registry.h              |   3 +
 5 files changed, 180 insertions(+), 1 deletion(-)
 create mode 100644 crypto/asymmetric_keys/x509_rsassa.asn1

diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
index 28b91adba2ae..f79ed8e8ef8e 100644
--- a/crypto/asymmetric_keys/Makefile
+++ b/crypto/asymmetric_keys/Makefile
@@ -20,15 +20,18 @@ obj-$(CONFIG_X509_CERTIFICATE_PARSER) += x509_key_parser.o
 x509_key_parser-y := \
 	x509.asn1.o \
 	x509_akid.asn1.o \
+	x509_rsassa.asn1.o \
 	x509_cert_parser.o \
 	x509_public_key.o
 
 $(obj)/x509_cert_parser.o: \
 	$(obj)/x509.asn1.h \
-	$(obj)/x509_akid.asn1.h
+	$(obj)/x509_akid.asn1.h \
+	$(obj)/x509_rsassa.asn1.h
 
 $(obj)/x509.asn1.o: $(obj)/x509.asn1.c $(obj)/x509.asn1.h
 $(obj)/x509_akid.asn1.o: $(obj)/x509_akid.asn1.c $(obj)/x509_akid.asn1.h
+$(obj)/x509_rsassa.asn1.o: $(obj)/x509_rsassa.asn1.c $(obj)/x509_rsassa.asn1.h
 
 #
 # PKCS#8 private key handling
diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 52c9b455fc7d..3738355618cd 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -15,6 +15,7 @@
 #include "x509_parser.h"
 #include "x509.asn1.h"
 #include "x509_akid.asn1.h"
+#include "x509_rsassa.asn1.h"
 
 struct x509_parse_context {
 	struct x509_certificate	*cert;		/* Certificate being constructed */
@@ -38,6 +39,8 @@ struct x509_parse_context {
 	const void	*raw_akid;		/* Raw authorityKeyId in ASN.1 */
 	const void	*akid_raw_issuer;	/* Raw directoryName in authorityKeyId */
 	unsigned	akid_raw_issuer_size;
+	const void	*raw_sig_params;	/* Signature AlgorithmIdentifier.parameters */
+	unsigned	raw_sig_params_size;
 };
 
 /*
@@ -101,6 +104,15 @@ struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
 		}
 	}
 
+	if (strcmp(ctx->cert->sig->encoding, "pss") == 0) {
+		pr_devel("rsa enc=pss hash=%s mgf=%s mgf_hash=%s salt=0x%x tf=0x%x\n",
+			 ctx->cert->sig->hash_algo,
+			 ctx->cert->sig->mgf,
+			 ctx->cert->sig->mgf_hash_algo,
+			 ctx->cert->sig->salt_length,
+			 ctx->cert->sig->trailer_field);
+	}
+
 	ret = -ENOMEM;
 	cert->pub->key = kmemdup(ctx->key, ctx->key_size, GFP_KERNEL);
 	if (!cert->pub->key)
@@ -194,6 +206,7 @@ int x509_note_pkey_algo(void *context, size_t hdrlen,
 			const void *value, size_t vlen)
 {
 	struct x509_parse_context *ctx = context;
+	int ret = 0;
 
 	pr_debug("PubKey Algo: %u\n", ctx->last_oid);
 
@@ -238,6 +251,39 @@ int x509_note_pkey_algo(void *context, size_t hdrlen,
 	case OID_SM2_with_SM3:
 		ctx->cert->sig->hash_algo = "sm3";
 		goto sm2;
+
+	case OID_rsassaPSS:
+		/* For rsassaPSS, the hash algorithm is packed as a mandatory
+		 * parameter in AlgorithmIdentifier.parameters.
+		 */
+		if (ctx->raw_sig_params == NULL && ctx->raw_sig_params_size != 1)
+			return -EBADMSG;
+
+		ctx->cert->sig->pkey_algo = "rsa";
+		ctx->cert->sig->encoding = "pss";
+		ctx->algo_oid = ctx->last_oid;
+		if (ctx->raw_sig_params) {
+			ret = asn1_ber_decoder(&x509_rsassa_decoder, ctx,
+					       ctx->raw_sig_params,
+					       ctx->raw_sig_params_size);
+			if (ret < 0)
+				return ret;
+		}
+
+		/* Fill in RSASSA-PSS-params defaults if left out. */
+		if (!ctx->cert->sig->hash_algo)
+			ctx->cert->sig->hash_algo = "sha1";
+		if (!ctx->cert->sig->mgf)
+			ctx->cert->sig->mgf = "mgf1";
+		if (!ctx->cert->sig->mgf_hash_algo)
+			ctx->cert->sig->mgf_hash_algo = "sha1";
+		ctx->cert->sig->trailer_field = 0xbc;
+
+		/* Reject if digest and mgf use different hashalgs. */
+		if (strcmp(ctx->cert->sig->hash_algo, ctx->cert->sig->mgf_hash_algo) != 0)
+			return -ENOPKG;
+
+		return 0;
 	}
 
 rsa_pkcs1:
@@ -439,6 +485,18 @@ int x509_note_params(void *context, size_t hdrlen,
 {
 	struct x509_parse_context *ctx = context;
 
+	if (ctx->last_oid == OID_rsassaPSS && !ctx->raw_sig_params) {
+		/* Stash AlgorithmIdentifier.parameters for RSASSA-PSS. */
+		ctx->raw_sig_params_size = vlen + hdrlen;
+		if (ctx->raw_sig_params_size) {
+			ctx->raw_sig_params = value - hdrlen;
+		} else {
+			ctx->raw_sig_params = NULL;
+			ctx->raw_sig_params_size = 1;
+		}
+		return 0;
+	}
+
 	/*
 	 * AlgorithmIdentifier is used three times in the x509, we should skip
 	 * first and ignore third, using second one which is after subject and
@@ -705,3 +763,97 @@ int x509_akid_note_serial(void *context, size_t hdrlen,
 	ctx->cert->sig->auth_ids[0] = kid;
 	return 0;
 }
+
+int x509_note_hash_algo(void *context, size_t hdrlen,
+			unsigned char tag,
+			const void *value, size_t vlen)
+{
+	struct x509_parse_context *ctx = context;
+	const char **ptr = NULL;
+
+	if (ctx->last_oid != OID_rsassaPSS)
+		return -EBADMSG;
+
+	if (ctx->cert->sig->mgf)
+		ptr = &ctx->cert->sig->mgf_hash_algo;
+	else
+		ptr = &ctx->cert->sig->hash_algo;
+
+	switch (look_up_OID(value, vlen)) {
+	case OID_sha224:
+		*ptr = "sha224";
+		break;
+	case OID_sha256:
+		*ptr = "sha256";
+		break;
+	case OID_sha384:
+		*ptr = "sha384";
+		break;
+	case OID_sha512:
+		*ptr = "sha512";
+		break;
+	case OID_sha1:
+	default:
+		*ptr = "sha1";
+		break;
+	}
+
+	return 0;
+}
+
+int x509_note_hash_algo_params(void *context, size_t hdrlen,
+			       unsigned char tag,
+			       const void *value, size_t vlen)
+{
+	return -EOPNOTSUPP;
+}
+
+int x509_note_mgf(void *context, size_t hdrlen,
+		  unsigned char tag,
+		  const void *value, size_t vlen)
+{
+	struct x509_parse_context *ctx = context;
+
+	if (ctx->last_oid != OID_rsassaPSS)
+		return -EBADMSG;
+
+	/* RFC8017 PKCS1MGFAlgorithms */
+	if (look_up_OID(value, vlen) != OID_mgf1)
+		return -EINVAL;
+
+	ctx->cert->sig->mgf = "mgf1";
+
+	return 0;
+}
+
+int x509_note_salt_length(void *context, size_t hdrlen,
+			  unsigned char tag,
+			  const void *value, size_t vlen)
+{
+	struct x509_parse_context *ctx = context;
+
+	if (ctx->last_oid != OID_rsassaPSS)
+		return -EBADMSG;
+
+	if (!value || !vlen || vlen > sizeof(ctx->cert->sig->salt_length))
+		return -EINVAL;
+
+	ctx->cert->sig->salt_length = (vlen == 2) ?
+		be16_to_cpu(*((u16 *) value)) : *((u8 *) value);
+
+	return 0;
+}
+
+int x509_note_trailer_field(void *context, size_t hdrlen,
+			    unsigned char tag,
+			    const void *value, size_t vlen)
+{
+	struct x509_parse_context *ctx = context;
+
+	if (ctx->last_oid != OID_rsassaPSS)
+		return -EBADMSG;
+
+	/* trailerField 0xbc per RFC8017 A.2.3 regardless of if
+	 * specified. */
+	return 0;
+}
diff --git a/crypto/asymmetric_keys/x509_rsassa.asn1 b/crypto/asymmetric_keys/x509_rsassa.asn1
new file mode 100644
index 000000000000..e524b978856d
--- /dev/null
+++ b/crypto/asymmetric_keys/x509_rsassa.asn1
@@ -0,0 +1,17 @@
+-- RFC8017
+RSASSA-PSS-params ::= SEQUENCE {
+	hashAlgorithm      [0] HashAlgorithm DEFAULT,
+	maskGenAlgorithm   [1] MaskGenAlgorithm DEFAULT,
+	saltLength         [2] INTEGER DEFAULT ({ x509_note_salt_length }),
+	trailerField       [3] INTEGER DEFAULT ({ x509_note_trailer_field })
+}
+
+HashAlgorithm ::= SEQUENCE {
+	algorithm		OBJECT IDENTIFIER ({ x509_note_hash_algo }),
+	parameters		ANY OPTIONAL ({ x509_note_hash_algo_params })
+}
+
+MaskGenAlgorithm ::= SEQUENCE {
+	mgf	OBJECT IDENTIFIER ({ x509_note_mgf }),
+	parameters	HashAlgorithm
+}
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 47accec68cb0..f36834c8bb13 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -46,6 +46,10 @@ struct public_key_signature {
 	const char *encoding;
 	const void *data;
 	unsigned int data_size;
+	const char *mgf;
+	const char *mgf_hash_algo;
+	u16 salt_length;
+	u16 trailer_field;
 };
 
 extern void public_key_signature_free(struct public_key_signature *sig);
diff --git a/include/linux/oid_registry.h b/include/linux/oid_registry.h
index 4462ed2c18cd..c247adc8a41e 100644
--- a/include/linux/oid_registry.h
+++ b/include/linux/oid_registry.h
@@ -113,6 +113,9 @@ enum OID {
 	OID_SM2_with_SM3,		/* 1.2.156.10197.1.501 */
 	OID_sm3WithRSAEncryption,	/* 1.2.156.10197.1.504 */
 
+	OID_mgf1,			/* 1.2.840.113549.1.1.8 */
+	OID_rsassaPSS,			/* 1.2.840.113549.1.1.10 */
+
 	OID__NR
 };
 
-- 
2.30.2