x509_cert_parser.c

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/* X.509 certificate parser
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * 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) "X.509: "fmt
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/oid_registry.h>
#include "public_key.h"
#include "x509_parser.h"
#include "x509-asn1.h"
#include "x509_rsakey-asn1.h"

struct x509_parse_context {
    struct x509_certificate *cert;      /* Certificate being constructed */
    unsigned long   data;           /* Start of data */
    const void  *cert_start;        /* Start of cert content */
    const void  *key;           /* Key data */
    size_t      key_size;       /* Size of key data */
    enum OID    last_oid;       /* Last OID encountered */
    enum OID    algo_oid;       /* Algorithm OID */
    unsigned char   nr_mpi;         /* Number of MPIs stored */
    u8      o_size;         /* Size of organizationName (O) */
    u8      cn_size;        /* Size of commonName (CN) */
    u8      email_size;     /* Size of emailAddress */
    u16     o_offset;       /* Offset of organizationName (O) */
    u16     cn_offset;      /* Offset of commonName (CN) */
    u16     email_offset;       /* Offset of emailAddress */
};

/*
 * Free an X.509 certificate
 */
void x509_free_certificate(struct x509_certificate *cert)
{
    if (cert) {
        public_key_destroy(cert->pub);
        kfree(cert->issuer);
        kfree(cert->subject);
        kfree(cert->fingerprint);
        kfree(cert->authority);
        kfree(cert);
    }
}

/*
 * Parse an X.509 certificate
 */
struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
{
    struct x509_certificate *cert;
    struct x509_parse_context *ctx;
    long ret;

    ret = -ENOMEM;
    cert = kzalloc(sizeof(struct x509_certificate), GFP_KERNEL);
    if (!cert)
        goto error_no_cert;
    cert->pub = kzalloc(sizeof(struct public_key), GFP_KERNEL);
    if (!cert->pub)
        goto error_no_ctx;
    ctx = kzalloc(sizeof(struct x509_parse_context), GFP_KERNEL);
    if (!ctx)
        goto error_no_ctx;

    ctx->cert = cert;
    ctx->data = (unsigned long)data;

    /* Attempt to decode the certificate */
    ret = asn1_ber_decoder(&x509_decoder, ctx, data, datalen);
    if (ret < 0)
        goto error_decode;

    /* Decode the public key */
    ret = asn1_ber_decoder(&x509_rsakey_decoder, ctx,
                   ctx->key, ctx->key_size);
    if (ret < 0)
        goto error_decode;

    kfree(ctx);
    return cert;

error_decode:
    kfree(ctx);
error_no_ctx:
    x509_free_certificate(cert);
error_no_cert:
    return ERR_PTR(ret);
}

/*
 * Note an OID when we find one for later processing when we know how
 * to interpret it.
 */
int x509_note_OID(void *context, size_t hdrlen,
         unsigned char tag,
         const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;

    ctx->last_oid = look_up_OID(value, vlen);
    if (ctx->last_oid == OID__NR) {
        char buffer[50];
        sprint_oid(value, vlen, buffer, sizeof(buffer));
        pr_debug("Unknown OID: [%lu] %s\n",
             (unsigned long)value - ctx->data, buffer);
    }
    return 0;
}

/*
 * Save the position of the TBS data so that we can check the signature over it
 * later.
 */
int x509_note_tbs_certificate(void *context, size_t hdrlen,
                  unsigned char tag,
                  const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;

    pr_debug("x509_note_tbs_certificate(,%zu,%02x,%ld,%zu)!\n",
         hdrlen, tag, (unsigned long)value - ctx->data, vlen);

    ctx->cert->tbs = value - hdrlen;
    ctx->cert->tbs_size = vlen + hdrlen;
    return 0;
}

/*
 * Record the public key algorithm
 */
int x509_note_pkey_algo(void *context, size_t hdrlen,
            unsigned char tag,
            const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;

    pr_debug("PubKey Algo: %u\n", ctx->last_oid);

    switch (ctx->last_oid) {
    case OID_md2WithRSAEncryption:
    case OID_md3WithRSAEncryption:
    default:
        return -ENOPKG; /* Unsupported combination */

    case OID_md4WithRSAEncryption:
        ctx->cert->sig_hash_algo = PKEY_HASH_MD5;
        ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
        break;

    case OID_sha1WithRSAEncryption:
        ctx->cert->sig_hash_algo = PKEY_HASH_SHA1;
        ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
        break;

    case OID_sha256WithRSAEncryption:
        ctx->cert->sig_hash_algo = PKEY_HASH_SHA256;
        ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
        break;

    case OID_sha384WithRSAEncryption:
        ctx->cert->sig_hash_algo = PKEY_HASH_SHA384;
        ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
        break;

    case OID_sha512WithRSAEncryption:
        ctx->cert->sig_hash_algo = PKEY_HASH_SHA512;
        ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
        break;

    case OID_sha224WithRSAEncryption:
        ctx->cert->sig_hash_algo = PKEY_HASH_SHA224;
        ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
        break;
    }

    ctx->algo_oid = ctx->last_oid;
    return 0;
}

/*
 * Note the whereabouts and type of the signature.
 */
int x509_note_signature(void *context, size_t hdrlen,
            unsigned char tag,
            const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;

    pr_debug("Signature type: %u size %zu\n", ctx->last_oid, vlen);

    if (ctx->last_oid != ctx->algo_oid) {
        pr_warn("Got cert with pkey (%u) and sig (%u) algorithm OIDs\n",
            ctx->algo_oid, ctx->last_oid);
        return -EINVAL;
    }

    ctx->cert->sig = value;
    ctx->cert->sig_size = vlen;
    return 0;
}

/*
 * Note some of the name segments from which we'll fabricate a name.
 */
int x509_extract_name_segment(void *context, size_t hdrlen,
                  unsigned char tag,
                  const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;

    switch (ctx->last_oid) {
    case OID_commonName:
        ctx->cn_size = vlen;
        ctx->cn_offset = (unsigned long)value - ctx->data;
        break;
    case OID_organizationName:
        ctx->o_size = vlen;
        ctx->o_offset = (unsigned long)value - ctx->data;
        break;
    case OID_email_address:
        ctx->email_size = vlen;
        ctx->email_offset = (unsigned long)value - ctx->data;
        break;
    default:
        break;
    }

    return 0;
}

/*
 * Fabricate and save the issuer and subject names
 */
static int x509_fabricate_name(struct x509_parse_context *ctx, size_t hdrlen,
                   unsigned char tag,
                   char **_name, size_t vlen)
{
    const void *name, *data = (const void *)ctx->data;
    size_t namesize;
    char *buffer;

    if (*_name)
        return -EINVAL;

    /* Empty name string if no material */
    if (!ctx->cn_size && !ctx->o_size && !ctx->email_size) {
        buffer = kmalloc(1, GFP_KERNEL);
        if (!buffer)
            return -ENOMEM;
        buffer[0] = 0;
        goto done;
    }

    if (ctx->cn_size && ctx->o_size) {
        /* Consider combining O and CN, but use only the CN if it is
         * prefixed by the O, or a significant portion thereof.
         */
        namesize = ctx->cn_size;
        name = data + ctx->cn_offset;
        if (ctx->cn_size >= ctx->o_size &&
            memcmp(data + ctx->cn_offset, data + ctx->o_offset,
               ctx->o_size) == 0)
            goto single_component;
        if (ctx->cn_size >= 7 &&
            ctx->o_size >= 7 &&
            memcmp(data + ctx->cn_offset, data + ctx->o_offset, 7) == 0)
            goto single_component;

        buffer = kmalloc(ctx->o_size + 2 + ctx->cn_size + 1,
                 GFP_KERNEL);
        if (!buffer)
            return -ENOMEM;

        memcpy(buffer,
               data + ctx->o_offset, ctx->o_size);
        buffer[ctx->o_size + 0] = ':';
        buffer[ctx->o_size + 1] = ' ';
        memcpy(buffer + ctx->o_size + 2,
               data + ctx->cn_offset, ctx->cn_size);
        buffer[ctx->o_size + 2 + ctx->cn_size] = 0;
        goto done;

    } else if (ctx->cn_size) {
        namesize = ctx->cn_size;
        name = data + ctx->cn_offset;
    } else if (ctx->o_size) {
        namesize = ctx->o_size;
        name = data + ctx->o_offset;
    } else {
        namesize = ctx->email_size;
        name = data + ctx->email_offset;
    }

single_component:
    buffer = kmalloc(namesize + 1, GFP_KERNEL);
    if (!buffer)
        return -ENOMEM;
    memcpy(buffer, name, namesize);
    buffer[namesize] = 0;

done:
    *_name = buffer;
    ctx->cn_size = 0;
    ctx->o_size = 0;
    ctx->email_size = 0;
    return 0;
}

int x509_note_issuer(void *context, size_t hdrlen,
             unsigned char tag,
             const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;
    return x509_fabricate_name(ctx, hdrlen, tag, &ctx->cert->issuer, vlen);
}

int x509_note_subject(void *context, size_t hdrlen,
              unsigned char tag,
              const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;
    return x509_fabricate_name(ctx, hdrlen, tag, &ctx->cert->subject, vlen);
}

/*
 * Extract the data for the public key algorithm
 */
int x509_extract_key_data(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_rsaEncryption)
        return -ENOPKG;

    /* There seems to be an extraneous 0 byte on the front of the data */
    ctx->cert->pkey_algo = PKEY_ALGO_RSA;
    ctx->key = value + 1;
    ctx->key_size = vlen - 1;
    return 0;
}

/*
 * Extract a RSA public key value
 */
int rsa_extract_mpi(void *context, size_t hdrlen,
            unsigned char tag,
            const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;
    MPI mpi;

    if (ctx->nr_mpi >= ARRAY_SIZE(ctx->cert->pub->mpi)) {
        pr_err("Too many public key MPIs in certificate\n");
        return -EBADMSG;
    }

    mpi = mpi_read_raw_data(value, vlen);
    if (!mpi)
        return -ENOMEM;

    ctx->cert->pub->mpi[ctx->nr_mpi++] = mpi;
    return 0;
}

/*
 * Process certificate extensions that are used to qualify the certificate.
 */
int x509_process_extension(void *context, size_t hdrlen,
               unsigned char tag,
               const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;
    const unsigned char *v = value;
    char *f;
    int i;

    pr_debug("Extension: %u\n", ctx->last_oid);

    if (ctx->last_oid == OID_subjectKeyIdentifier) {
        /* Get hold of the key fingerprint */
        if (vlen < 3)
            return -EBADMSG;
        if (v[0] != ASN1_OTS || v[1] != vlen - 2)
            return -EBADMSG;
        v += 2;
        vlen -= 2;

        f = kmalloc(vlen * 2 + 1, GFP_KERNEL);
        if (!f)
            return -ENOMEM;
        for (i = 0; i < vlen; i++)
            sprintf(f + i * 2, "%02x", v[i]);
        pr_debug("fingerprint %s\n", f);
        ctx->cert->fingerprint = f;
        return 0;
    }

    if (ctx->last_oid == OID_authorityKeyIdentifier) {
        /* Get hold of the CA key fingerprint */
        if (vlen < 5)
            return -EBADMSG;
        if (v[0] != (ASN1_SEQ | (ASN1_CONS << 5)) ||
            v[1] != vlen - 2 ||
            v[2] != (ASN1_CONT << 6) ||
            v[3] != vlen - 4)
            return -EBADMSG;
        v += 4;
        vlen -= 4;

        f = kmalloc(vlen * 2 + 1, GFP_KERNEL);
        if (!f)
            return -ENOMEM;
        for (i = 0; i < vlen; i++)
            sprintf(f + i * 2, "%02x", v[i]);
        pr_debug("authority   %s\n", f);
        ctx->cert->authority = f;
        return 0;
    }

    return 0;
}

/*
 * Record a certificate time.
 */
static int x509_note_time(struct tm *tm,  size_t hdrlen,
              unsigned char tag,
              const unsigned char *value, size_t vlen)
{
    const unsigned char *p = value;

#define dec2bin(X) ((X) - '0')
#define DD2bin(P) ({ unsigned x = dec2bin(P[0]) * 10 + dec2bin(P[1]); P += 2; x; })

    if (tag == ASN1_UNITIM) {
        /* UTCTime: YYMMDDHHMMSSZ */
        if (vlen != 13)
            goto unsupported_time;
        tm->tm_year = DD2bin(p);
        if (tm->tm_year >= 50)
            tm->tm_year += 1900;
        else
            tm->tm_year += 2000;
    } else if (tag == ASN1_GENTIM) {
        /* GenTime: YYYYMMDDHHMMSSZ */
        if (vlen != 15)
            goto unsupported_time;
        tm->tm_year = DD2bin(p) * 100 + DD2bin(p);
    } else {
        goto unsupported_time;
    }

    tm->tm_year -= 1900;
    tm->tm_mon  = DD2bin(p) - 1;
    tm->tm_mday = DD2bin(p);
    tm->tm_hour = DD2bin(p);
    tm->tm_min  = DD2bin(p);
    tm->tm_sec  = DD2bin(p);

    if (*p != 'Z')
        goto unsupported_time;

    return 0;

unsupported_time:
    pr_debug("Got unsupported time [tag %02x]: '%*.*s'\n",
         tag, (int)vlen, (int)vlen, value);
    return -EBADMSG;
}

int x509_note_not_before(void *context, size_t hdrlen,
             unsigned char tag,
             const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;
    return x509_note_time(&ctx->cert->valid_from, hdrlen, tag, value, vlen);
}

int x509_note_not_after(void *context, size_t hdrlen,
            unsigned char tag,
            const void *value, size_t vlen)
{
    struct x509_parse_context *ctx = context;
    return x509_note_time(&ctx->cert->valid_to, hdrlen, tag, value, vlen);
}