pefile: Parse the "Microsoft individual code signing" data blob

The PKCS#7 certificate should contain a "Microsoft individual code signing"
data blob as its signed content.  This blob contains a digest of the signed
content of the PE binary and the OID of the digest algorithm used (typically
SHA256).

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

5 files changed, 168 insertions, 1 deletions

diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
index 3e4de5297015..e47fcd9ac5e8 100644
--- a/crypto/asymmetric_keys/Makefile
+++ b/crypto/asymmetric_keys/Makefile
@@ -54,4 +54,11 @@ pkcs7_test_key-y := \
 obj-$(CONFIG_SIGNED_PE_FILE_VERIFICATION) += verify_signed_pefile.o
 
 verify_signed_pefile-y := \
-        verify_pefile.o
+        verify_pefile.o \
+        mscode_parser.o \
+        mscode-asn1.o
+
+$(obj)/mscode_parser.o: $(obj)/mscode-asn1.h $(obj)/mscode-asn1.h
+$(obj)/mscode-asn1.o: $(obj)/mscode-asn1.c $(obj)/mscode-asn1.h
+
+clean-files     += mscode-asn1.c mscode-asn1.h
diff --git a/crypto/asymmetric_keys/mscode.asn1 b/crypto/asymmetric_keys/mscode.asn1
new file mode 100644
index 000000000000..6d09ba48c41c
--- /dev/null
+++ b/crypto/asymmetric_keys/mscode.asn1
@@ -0,0 +1,28 @@
+--- Microsoft individual code signing data blob parser
+---
+--- Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+--- Written by David Howells (dhowells@redhat.com)
+---
+--- This program is free software; you can redistribute it and/or
+--- modify it under the terms of the GNU General Public Licence
+--- as published by the Free Software Foundation; either version
+--- 2 of the Licence, or (at your option) any later version.
+---
+
+MSCode ::= SEQUENCE {
+        type                    SEQUENCE {
+                contentType     ContentType,
+                parameters      ANY
+        },
+        content                 SEQUENCE {
+                digestAlgorithm DigestAlgorithmIdentifier,
+                digest          OCTET STRING ({ mscode_note_digest })
+        }
+}
+
+ContentType ::= OBJECT IDENTIFIER ({ mscode_note_content_type })
+
+DigestAlgorithmIdentifier ::= SEQUENCE {
+        algorithm   OBJECT IDENTIFIER ({ mscode_note_digest_algo }),
+        parameters  ANY OPTIONAL
+}
diff --git a/crypto/asymmetric_keys/mscode_parser.c b/crypto/asymmetric_keys/mscode_parser.c
new file mode 100644
index 000000000000..09336c32b3d4
--- /dev/null
+++ b/crypto/asymmetric_keys/mscode_parser.c
@@ -0,0 +1,120 @@
+/* Parse a Microsoft Individual Code Signing blob
+ *
+ * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) "MSCODE: "fmt
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/oid_registry.h>
+#include <crypto/pkcs7.h>
+#include "verify_pefile.h"
+#include "mscode-asn1.h"
+
+/*
+ * Parse a Microsoft Individual Code Signing blob
+ */
+int mscode_parse(struct pefile_context *ctx)
+{
+        const void *content_data;
+        size_t data_len;
+        int ret;
+
+        ret = pkcs7_get_content_data(ctx->pkcs7, &content_data, &data_len, 1);
+
+        if (ret) {
+                pr_debug("PKCS#7 message does not contain data\n");
+                return ret;
+        }
+
+        pr_devel("Data: %zu [%*ph]\n", data_len, (unsigned)(data_len),
+                 content_data);
+
+        return asn1_ber_decoder(&mscode_decoder, ctx, content_data, data_len);
+}
+
+/*
+ * Check the content type OID
+ */
+int mscode_note_content_type(void *context, size_t hdrlen,
+                             unsigned char tag,
+                             const void *value, size_t vlen)
+{
+        enum OID oid;
+
+        oid = look_up_OID(value, vlen);
+        if (oid == OID__NR) {
+                char buffer[50];
+
+                sprint_oid(value, vlen, buffer, sizeof(buffer));
+                pr_err("Unknown OID: %s\n", buffer);
+                return -EBADMSG;
+        }
+
+        if (oid != OID_msIndividualSPKeyPurpose) {
+                pr_err("Unexpected content type OID %u\n", oid);
+                return -EBADMSG;
+        }
+
+        return 0;
+}
+
+/*
+ * Note the digest algorithm OID
+ */
+int mscode_note_digest_algo(void *context, size_t hdrlen,
+                            unsigned char tag,
+                            const void *value, size_t vlen)
+{
+        struct pefile_context *ctx = context;
+        char buffer[50];
+        enum OID oid;
+
+        oid = look_up_OID(value, vlen);
+        switch (oid) {
+        case OID_md4:
+                ctx->digest_algo = HASH_ALGO_MD4;
+                break;
+        case OID_md5:
+                ctx->digest_algo = HASH_ALGO_MD5;
+                break;
+        case OID_sha1:
+                ctx->digest_algo = HASH_ALGO_SHA1;
+                break;
+        case OID_sha256:
+                ctx->digest_algo = HASH_ALGO_SHA256;
+                break;
+
+        case OID__NR:
+                sprint_oid(value, vlen, buffer, sizeof(buffer));
+                pr_err("Unknown OID: %s\n", buffer);
+                return -EBADMSG;
+
+        default:
+                pr_err("Unsupported content type: %u\n", oid);
+                return -ENOPKG;
+        }
+
+        return 0;
+}
+
+/*
+ * Note the digest we're guaranteeing with this certificate
+ */
+int mscode_note_digest(void *context, size_t hdrlen,
+                       unsigned char tag,
+                       const void *value, size_t vlen)
+{
+        struct pefile_context *ctx = context;
+
+        ctx->digest = value;
+        ctx->digest_len = vlen;
+        return 0;
+}
diff --git a/crypto/asymmetric_keys/verify_pefile.c b/crypto/asymmetric_keys/verify_pefile.c
index 13f3b44b5046..b975918e82d2 100644
--- a/crypto/asymmetric_keys/verify_pefile.c
+++ b/crypto/asymmetric_keys/verify_pefile.c
@@ -245,6 +245,13 @@ int verify_pefile_signature(const void *pebuf, unsigned pelen,
                 goto error;
         }
 
+        ret = mscode_parse(&ctx);
+        if (ret < 0)
+                goto error;
+
+        pr_debug("Digest: %u [%*ph]\n",
+                 ctx.digest_len, ctx.digest_len, ctx.digest);
+
         ret = -ENOANO; // Not yet complete
 
 error:
diff --git a/crypto/asymmetric_keys/verify_pefile.h b/crypto/asymmetric_keys/verify_pefile.h
index e165d23458d4..55d5f7ebc45a 100644
--- a/crypto/asymmetric_keys/verify_pefile.h
+++ b/crypto/asymmetric_keys/verify_pefile.h
@@ -35,3 +35,8 @@ struct pefile_context {
         pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__)
 #define kleave(FMT, ...) \
         pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
+
+/*
+ * mscode_parser.c
+ */
+extern int mscode_parse(struct pefile_context *ctx);