libkmod: Return module signature information in kmod_module_get_info()

If the module is built with CONFIG_MODULE_SIG, add the the signer's
name, hexadecimal key id and hash algorithm to the list returned in
kmod_module_get_info(). The modinfo output then looks like this:

filename:       /home/mmarek/kmod/testsuite/rootfs-pristine/test-modinfo/ext4-x86_64-sha256.ko
license:        GPL
description:    Fourth Extended Filesystem
author:         Remy Card, Stephen Tweedie, Andrew Morton, Andreas Dilger, Theodore Ts'o and others
alias:          ext3
alias:          ext2
depends:        mbcache,jbd2
intree:         Y
vermagic:       3.7.0 SMP mod_unload
signer:         Magrathea: Glacier signing key
sig_key:        E3:C8:FC:A7:3F:B3:1D:DE:84:81:EF:38:E3:4C:DE:4B:0C:FD:1B:F9
sig_hashalgo:   sha256

The signature algorithm (RSA) and key identifier type (X509) are not
displayed, because they are constant information for every signed
module. But it would be trivial to add this. Note: No attempt is made at
verifying the signature, I don't think that modinfo is the right tool
for this.

1 files changed, 141 insertions, 0 deletions

diff --git a/libkmod/libkmod-signature.c b/libkmod/libkmod-signature.c
new file mode 100644
index 0000000..6b80caa
--- /dev/null
+++ b/libkmod/libkmod-signature.c
@@ -0,0 +1,141 @@
+/*
+ * libkmod - module signature display
+ *
+ * Copyright (C) 2013 Michal Marek, SUSE
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include <endian.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "libkmod-private.h"
+
+/* These types and tables were copied from the 3.7 kernel sources.
+ * As this is just description of the signature format, it should not be
+ * considered derived work (so libkmod can use the LGPL license).
+ */
+enum pkey_algo {
+	PKEY_ALGO_DSA,
+	PKEY_ALGO_RSA,
+	PKEY_ALGO__LAST
+};
+
+static const char *const pkey_algo[PKEY_ALGO__LAST] = {
+	[PKEY_ALGO_DSA]		= "DSA",
+	[PKEY_ALGO_RSA]		= "RSA",
+};
+
+enum pkey_hash_algo {
+	PKEY_HASH_MD4,
+	PKEY_HASH_MD5,
+	PKEY_HASH_SHA1,
+	PKEY_HASH_RIPE_MD_160,
+	PKEY_HASH_SHA256,
+	PKEY_HASH_SHA384,
+	PKEY_HASH_SHA512,
+	PKEY_HASH_SHA224,
+	PKEY_HASH__LAST
+};
+
+const char *const pkey_hash_algo[PKEY_HASH__LAST] = {
+	[PKEY_HASH_MD4]		= "md4",
+	[PKEY_HASH_MD5]		= "md5",
+	[PKEY_HASH_SHA1]	= "sha1",
+	[PKEY_HASH_RIPE_MD_160]	= "rmd160",
+	[PKEY_HASH_SHA256]	= "sha256",
+	[PKEY_HASH_SHA384]	= "sha384",
+	[PKEY_HASH_SHA512]	= "sha512",
+	[PKEY_HASH_SHA224]	= "sha224",
+};
+
+enum pkey_id_type {
+	PKEY_ID_PGP,		/* OpenPGP generated key ID */
+	PKEY_ID_X509,		/* X.509 arbitrary subjectKeyIdentifier */
+	PKEY_ID_TYPE__LAST
+};
+
+const char *const pkey_id_type[PKEY_ID_TYPE__LAST] = {
+	[PKEY_ID_PGP]		= "PGP",
+	[PKEY_ID_X509]		= "X509",
+};
+
+/*
+ * Module signature information block.
+ *
+ * The constituents of the signature section are, in order:
+ *
+ *	- Signer's name
+ *	- Key identifier
+ *	- Signature data
+ *	- Information block
+ */
+struct module_signature {
+	uint8_t algo;        /* Public-key crypto algorithm [enum pkey_algo] */
+	uint8_t hash;        /* Digest algorithm [enum pkey_hash_algo] */
+	uint8_t id_type;     /* Key identifier type [enum pkey_id_type] */
+	uint8_t signer_len;  /* Length of signer's name */
+	uint8_t key_id_len;  /* Length of key identifier */
+	uint8_t __pad[3];
+	uint32_t sig_len;    /* Length of signature data (big endian) */
+};
+
+#define SIG_MAGIC "~Module signature appended~\n"
+
+bool kmod_module_signature_info(const struct kmod_file *file, struct kmod_signature_info *sig_info)
+{
+	const char *mem;
+	off_t size;
+	const struct module_signature *modsig;
+	size_t sig_len;
+
+
+	size = kmod_file_get_size(file);
+	mem = kmod_file_get_contents(file);
+	if (size < (off_t)strlen(SIG_MAGIC))
+		return false;
+	size -= strlen(SIG_MAGIC);
+	if (memcmp(SIG_MAGIC, mem + size, strlen(SIG_MAGIC)) != 0)
+		return false;
+
+	if (size < (off_t)sizeof(struct module_signature))
+		return false;
+	size -= sizeof(struct module_signature);
+	modsig = (struct module_signature *)(mem + size);
+	if (modsig->algo >= PKEY_ALGO__LAST ||
+			modsig->hash >= PKEY_HASH__LAST ||
+			modsig->id_type >= PKEY_ID_TYPE__LAST)
+		return false;
+	sig_len = be32toh(modsig->sig_len);
+	if (size < (off_t)(modsig->signer_len + modsig->key_id_len + sig_len))
+		return false;
+
+	size -= modsig->key_id_len + sig_len;
+	sig_info->key_id = mem + size;
+	sig_info->key_id_len = modsig->key_id_len;
+
+	size -= modsig->signer_len;
+	sig_info->signer = mem + size;
+	sig_info->signer_len = modsig->signer_len;
+
+	sig_info->algo = pkey_algo[modsig->algo];
+	sig_info->hash_algo = pkey_hash_algo[modsig->hash];
+	sig_info->id_type = pkey_id_type[modsig->id_type];
+
+	return true;
+}