sign-file.c

//
// Created by Stefan Schwarz on 28.12.17.
//

/* Sign a module file using the given key. */

#include <stdio.h>
#include <stdlib.h>
//#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <getopt.h>
#include <err.h>
//#include <arpa/inet.h>
#include <openssl/opensslv.h>
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <openssl/pem.h>
#include <openssl/err.h>
#include <openssl/engine.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] */
    uint8_t		id_type;	/* Key identifier type [PKEY_ID_PKCS7] */
    uint8_t		signer_len;	/* Length of signer's name [0] */
    uint8_t		key_id_len;	/* Length of key identifier [0] */
    uint8_t		__pad[3];
    uint32_t	sig_len;	/* Length of signature data */
};

#define PKEY_ID_PKCS7 2

static char magic_number[] = "~Module signature appended~\n";

static __attribute__((noreturn))
void format(void)
{
    fprintf(stderr,
            "Usage: scripts/sign-file [-dp] <hash algo> <key> <x509> <module> [<dest>]\n");
    fprintf(stderr,
            "       scripts/sign-file -s <raw sig> <hash algo> <x509> <module> [<dest>]\n");
    exit(2);
}

static void display_openssl_errors(int l)
{
    const char *file;
    char buf[120];
    int e, line;

    if (ERR_peek_error() == 0)
        return;
    fprintf(stderr, "At main.c:%d:\n", l);

    while ((e = ERR_get_error_line(&file, &line))) {
        ERR_error_string(e, buf);
        fprintf(stderr, "- SSL %s: %s:%d\n", buf, file, line);
    }
}

static void drain_openssl_errors(void)
{
    const char *file;
    int line;

    if (ERR_peek_error() == 0)
        return;
    while (ERR_get_error_line(&file, &line)) {}
}

#define ERR(cond, fmt, ...)				\
	do {						\
		bool __cond = (cond);			\
		display_openssl_errors(__LINE__);	\
		if (__cond) {				\
			err(1, fmt, ## __VA_ARGS__);	\
		}					\
	} while(0)

static const char *key_pass;

static int pem_pw_cb(char *buf, int len, int w, void *v)
{
    int pwlen;

    if (!key_pass)
        return -1;

    pwlen = (int) strlen(key_pass);
    if (pwlen >= len)
        return -1;

    strcpy(buf, key_pass);

    /* If it's wrong, don't keep trying it. */
    key_pass = NULL;

    return pwlen;
}

static EVP_PKEY *read_private_key(const char *private_key_name)
{
    EVP_PKEY *private_key;

    if (!strncmp(private_key_name, "pkcs11:", 7)) {
        ENGINE *e;

        ENGINE_load_builtin_engines();
        drain_openssl_errors();
        e = ENGINE_by_id("pkcs11");
        ERR(!e, "Load PKCS#11 ENGINE");
        if (ENGINE_init(e))
            drain_openssl_errors();
        else
            ERR(1, "ENGINE_init");
        if (key_pass)
            ERR(!ENGINE_ctrl_cmd_string(e, "PIN", key_pass, 0),
                "Set PKCS#11 PIN");
        private_key = ENGINE_load_private_key(e, private_key_name,
                                              NULL, NULL);
        ERR(!private_key, "%s", private_key_name);
    } else {
        BIO *b;

        b = BIO_new_file(private_key_name, "rb");
        ERR(!b, "%s", private_key_name);
        private_key = PEM_read_bio_PrivateKey(b, NULL, pem_pw_cb,
                                              NULL);
        ERR(!private_key, "%s", private_key_name);
        BIO_free(b);
    }

    return private_key;
}

static X509 *read_x509(const char *x509_name)
{
    unsigned char buf[2];
    X509 *x509;
    BIO *b;
    int n;

    b = BIO_new_file(x509_name, "rb");
    ERR(!b, "%s", x509_name);

    /* Look at the first two bytes of the file to determine the encoding */
    n = BIO_read(b, buf, 2);
    if (n != 2) {
        if (BIO_should_retry(b)) {
            fprintf(stderr, "%s: Read wanted retry\n", x509_name);
            exit(1);
        }
        if (n >= 0) {
            fprintf(stderr, "%s: Short read\n", x509_name);
            exit(1);
        }
        ERR(1, "%s", x509_name);
    }

    ERR(BIO_reset(b) != 0, "%s", x509_name);

    if (buf[0] == 0x30 && buf[1] >= 0x81 && buf[1] <= 0x84)
        /* Assume raw DER encoded X.509 */
        x509 = d2i_X509_bio(b, NULL);
    else
        /* Assume PEM encoded X.509 */
        x509 = PEM_read_bio_X509(b, NULL, NULL, NULL);

    BIO_free(b);
    ERR(!x509, "%s", x509_name);

    return x509;
}

int main(int argc, char **argv)
{
    struct module_signature sig_info = { .id_type = PKEY_ID_PKCS7 };
    char *hash_algo = NULL;
    char *private_key_name = NULL, *raw_sig_name = NULL;
    char *x509_name, *module_name, *dest_name;
    bool save_sig = false, replace_orig;
    bool sign_only = false;
    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;
    OpenSSL_add_all_algorithms();
    ERR_load_crypto_strings();
    ERR_clear_error();

    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();
        }
    } while (opt != -1);

    argc -= optind;
    argv += optind;
    if (argc < 4 || argc > 5)
        format();

    if (raw_sig) {
        raw_sig_name = argv[0];
        hash_algo = argv[1];
    } else {
        hash_algo = argv[0];
        private_key_name = argv[1];
    }
    x509_name = argv[2];
    module_name = argv[3];
    if (argc == 5 && strcmp(argv[3], argv[4]) != 0) {
        dest_name = argv[4];
        replace_orig = false;
    } else {
        ERR(asprintf(&dest_name, "%s.~signed~", module_name) < 0,
            "asprintf");
        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);

    if (!raw_sig) {
        /* Read the private key and the X.509 cert the PKCS#7 message
         * will point to.
         */
        private_key = read_private_key(private_key_name);
        x509 = read_x509(x509_name);

        /* Digest the module data. */
        OpenSSL_add_all_digests();
        display_openssl_errors(__LINE__);
        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 |
                               CMS_DETACHED | CMS_STREAM);
        ERR(!cms, "CMS_sign");

        ERR(!CMS_add1_signer(cms, x509, private_key, digest_algo,
                             CMS_NOCERTS | CMS_BINARY |
                                     CMS_NOSMIMECAP | use_keyid |
                                     use_signed_attrs),
            "CMS_add1_signer");
        ERR(CMS_final(cms, bm, NULL, CMS_NOCERTS | CMS_BINARY) < 0,
            "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;

            ERR(asprintf(&sig_file_name, "%s.p7s", module_name) < 0,
                "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) < 0,
                "%s", sig_file_name);
#else
            ERR(i2d_PKCS7_bio(b, pkcs7) < 0,
                "%s", sig_file_name);
#endif
            BIO_free(b);
        }

        if (sign_only) {
            BIO_free(bm);
            return 0;
        }
    }

    /* Open the destination file now so that we can shovel the module data
     * across as we read it.
     */
    bd = BIO_new_file(dest_name, "wb");
    ERR(!bd, "%s", dest_name);

    /* Append the marker and the PKCS#7 message to the destination file */
    ERR(BIO_reset(bm) < 0, "%s", module_name);
    while ((n = BIO_read(bm, buf, sizeof(buf))),
            n > 0) {
        ERR(BIO_write(bd, buf, n) < 0, "%s", dest_name);
    }
    BIO_free(bm);
    ERR(n < 0, "%s", module_name);
    module_size = BIO_number_written(bd);

    if (!raw_sig) {
#ifndef USE_PKCS7
        ERR(i2d_CMS_bio_stream(bd, cms, NULL, 0) < 0, "%s", dest_name);
#else
        ERR(i2d_PKCS7_bio(bd, pkcs7) < 0, "%s", dest_name);
#endif
    } else {
        BIO *b;

        /* Read the raw signature file and write the data to the
         * destination file
         */
        b = BIO_new_file(raw_sig_name, "rb");
        ERR(!b, "%s", raw_sig_name);
        while ((n = BIO_read(b, buf, sizeof(buf))), n > 0)
            ERR(BIO_write(bd, buf, n) < 0, "%s", dest_name);
        BIO_free(b);
    }

    sig_size = BIO_number_written(bd) - module_size;
    sig_info.sig_len = htonl(sig_size);
    ERR(BIO_write(bd, &sig_info, sizeof(sig_info)) < 0, "%s", dest_name);
    ERR(BIO_write(bd, magic_number, sizeof(magic_number) - 1) < 0, "%s", dest_name);

    ERR(BIO_free(bd) < 0, "%s", dest_name);

    /* Finally, if we're signing in place, replace the original. */
    if (replace_orig)
        ERR(rename(dest_name, module_name) < 0, "%s", dest_name);

    return 0;
}