PKCS#7: Support CMS messages also [RFC5652]

Since CMS is an evolution of PKCS#7, with much of the ASN.1 being
compatible, add support for CMS signed-data messages also [RFC5652 sec 5].

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

3 files changed, 68 insertions, 9 deletions

diff --git a/crypto/asymmetric_keys/pkcs7.asn1 b/crypto/asymmetric_keys/pkcs7.asn1
index 05504431e1c1..6bf8ff4f7414 100644
--- a/crypto/asymmetric_keys/pkcs7.asn1
+++ b/crypto/asymmetric_keys/pkcs7.asn1
@@ -69,7 +69,7 @@ SignerInfos ::= CHOICE {
 
 SignerInfo ::= SEQUENCE {
         version                 INTEGER ({ pkcs7_note_signerinfo_version }),
-        issuerAndSerialNumber   IssuerAndSerialNumber,
+        sid                     SignerIdentifier, -- CMS variant, not PKCS#7
         digestAlgorithm         DigestAlgorithmIdentifier ({ pkcs7_sig_note_digest_algo }),
         authenticatedAttributes CHOICE {
                 aaSet           [0] IMPLICIT SetOfAuthenticatedAttribute
@@ -88,6 +88,12 @@ SignerInfo ::= SEQUENCE {
         } OPTIONAL
 } ({ pkcs7_note_signed_info })
 
+SignerIdentifier ::= CHOICE {
+        -- RFC5652 sec 5.3
+        issuerAndSerialNumber IssuerAndSerialNumber,
+        subjectKeyIdentifier [0] IMPLICIT SubjectKeyIdentifier
+}
+
 IssuerAndSerialNumber ::= SEQUENCE {
         issuer                  Name ({ pkcs7_sig_note_issuer }),
         serialNumber            CertificateSerialNumber ({ pkcs7_sig_note_serial })
@@ -95,6 +101,8 @@ IssuerAndSerialNumber ::= SEQUENCE {
 
 CertificateSerialNumber ::= INTEGER
 
+SubjectKeyIdentifier ::= OCTET STRING ({ pkcs7_sig_note_skid })
+
 SetOfAuthenticatedAttribute ::= SET OF AuthenticatedAttribute
 
 AuthenticatedAttribute ::= SEQUENCE {
diff --git a/crypto/asymmetric_keys/pkcs7_parser.c b/crypto/asymmetric_keys/pkcs7_parser.c
index ab427f04b299..826e2f3f507b 100644
--- a/crypto/asymmetric_keys/pkcs7_parser.c
+++ b/crypto/asymmetric_keys/pkcs7_parser.c
@@ -33,6 +33,9 @@ struct pkcs7_parse_context {
         unsigned        raw_serial_size;
         unsigned        raw_issuer_size;
         const void      *raw_issuer;
+        const void      *raw_skid;
+        unsigned        raw_skid_size;
+        bool            expect_skid;
 };
 
 /*
@@ -249,15 +252,21 @@ int pkcs7_note_signeddata_version(void *context, size_t hdrlen,
                                   unsigned char tag,
                                   const void *value, size_t vlen)
 {
+        struct pkcs7_parse_context *ctx = context;
         unsigned version;
 
         if (vlen != 1)
                 goto unsupported;
 
-        version = *(const u8 *)value;
+        ctx->msg->version = version = *(const u8 *)value;
         switch (version) {
         case 1:
-                /* PKCS#7 SignedData [RFC2315 sec 9.1] */
+                /* PKCS#7 SignedData [RFC2315 sec 9.1]
+                 * CMS ver 1 SignedData [RFC5652 sec 5.1]
+                 */
+                break;
+        case 3:
+                /* CMS ver 3 SignedData [RFC2315 sec 5.1] */
                 break;
         default:
                 goto unsupported;
@@ -277,6 +286,7 @@ int pkcs7_note_signerinfo_version(void *context, size_t hdrlen,
                                   unsigned char tag,
                                   const void *value, size_t vlen)
 {
+        struct pkcs7_parse_context *ctx = context;
         unsigned version;
 
         if (vlen != 1)
@@ -285,7 +295,18 @@ int pkcs7_note_signerinfo_version(void *context, size_t hdrlen,
         version = *(const u8 *)value;
         switch (version) {
         case 1:
-                /* PKCS#7 SignerInfo [RFC2315 sec 9.2] */
+                /* PKCS#7 SignerInfo [RFC2315 sec 9.2]
+                 * CMS ver 1 SignerInfo [RFC5652 sec 5.3]
+                 */
+                if (ctx->msg->version != 1)
+                        goto version_mismatch;
+                ctx->expect_skid = false;
+                break;
+        case 3:
+                /* CMS ver 3 SignerInfo [RFC2315 sec 5.3] */
+                if (ctx->msg->version == 1)
+                        goto version_mismatch;
+                ctx->expect_skid = true;
                 break;
         default:
                 goto unsupported;
@@ -296,6 +317,9 @@ int pkcs7_note_signerinfo_version(void *context, size_t hdrlen,
 unsupported:
         pr_warn("Unsupported SignerInfo version\n");
         return -EINVAL;
+version_mismatch:
+        pr_warn("SignedData-SignerInfo version mismatch\n");
+        return -EBADMSG;
 }
 
 /*
@@ -440,6 +464,22 @@ int pkcs7_sig_note_issuer(void *context, size_t hdrlen,
 }
 
 /*
+ * Note the issuing cert's subjectKeyIdentifier
+ */
+int pkcs7_sig_note_skid(void *context, size_t hdrlen,
+                        unsigned char tag,
+                        const void *value, size_t vlen)
+{
+        struct pkcs7_parse_context *ctx = context;
+
+        pr_devel("SKID: %02x %zu [%*ph]\n", tag, vlen, (unsigned)vlen, value);
+
+        ctx->raw_skid = value;
+        ctx->raw_skid_size = vlen;
+        return 0;
+}
+
+/*
  * Note the signature data
  */
 int pkcs7_sig_note_signature(void *context, size_t hdrlen,
@@ -472,13 +512,21 @@ int pkcs7_note_signed_info(void *context, size_t hdrlen,
         struct asymmetric_key_id *kid;
 
         /* Generate cert issuer + serial number key ID */
-        kid = asymmetric_key_generate_id(ctx->raw_serial,
-                                         ctx->raw_serial_size,
-                                         ctx->raw_issuer,
-                                         ctx->raw_issuer_size);
+        if (!ctx->expect_skid) {
+                kid = asymmetric_key_generate_id(ctx->raw_serial,
+                                                 ctx->raw_serial_size,
+                                                 ctx->raw_issuer,
+                                                 ctx->raw_issuer_size);
+        } else {
+                kid = asymmetric_key_generate_id(ctx->raw_skid,
+                                                 ctx->raw_skid_size,
+                                                 "", 0);
+        }
         if (IS_ERR(kid))
                 return PTR_ERR(kid);
 
+        pr_devel("SINFO KID: %u [%*phN]\n", kid->len, kid->len, kid->data);
+
         sinfo->signing_cert_id = kid;
         sinfo->index = ++ctx->sinfo_index;
         *ctx->ppsinfo = sinfo;
diff --git a/crypto/asymmetric_keys/pkcs7_parser.h b/crypto/asymmetric_keys/pkcs7_parser.h
index efc7dc9b8f9c..790dd7cec82c 100644
--- a/crypto/asymmetric_keys/pkcs7_parser.h
+++ b/crypto/asymmetric_keys/pkcs7_parser.h
@@ -33,7 +33,9 @@ struct pkcs7_signed_info {
         unsigned        authattrs_len;
         const void      *authattrs;
 
-        /* Issuing cert serial number and issuer's name */
+        /* Issuing cert serial number and issuer's name [PKCS#7 or CMS ver 1]
+         * or issuing cert's SKID [CMS ver 3].
+         */
         struct asymmetric_key_id *signing_cert_id;
 
         /* Message signature.
@@ -50,6 +52,7 @@ struct pkcs7_message {
         struct x509_certificate *certs; /* Certificate list */
         struct x509_certificate *crl;   /* Revocation list */
         struct pkcs7_signed_info *signed_infos;
+        u8              version;        /* Version of cert (1 -> PKCS#7 or CMS; 3 -> CMS) */
 
         /* Content Data (or NULL) */
         enum OID        data_type;      /* Type of Data */