/* X.509 certificate 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.
 */

#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;
}

/* The keyIdentifier in AuthorityKeyIdentifier SEQUENCE is tag(CONT,PRIM,0) */
#define SEQ_TAG_KEYID (ASN1_CONT << 6)

/*
 * 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) {
                size_t key_len;

                /* Get hold of the CA key fingerprint */
                if (vlen < 5)
                        return -EBADMSG;

                /* Authority Key Identifier must be a Constructed SEQUENCE */
                if (v[0] != (ASN1_SEQ | (ASN1_CONS << 5)))
                        return -EBADMSG;

                /* Authority Key Identifier is not indefinite length */
                if (unlikely(vlen == ASN1_INDEFINITE_LENGTH))
                        return -EBADMSG;

                if (vlen < ASN1_INDEFINITE_LENGTH) {
                        /* Short Form length */
                        if (v[1] != vlen - 2 ||
                            v[2] != SEQ_TAG_KEYID ||
                            v[3] > vlen - 4)
                                return -EBADMSG;

                        key_len = v[3];
                        v += 4;
                } else {
                        /* Long Form length */
                        size_t seq_len = 0;
                        size_t sub = v[1] - ASN1_INDEFINITE_LENGTH;

                        if (sub > 2)
                                return -EBADMSG;

                        /* calculate the length from subsequent octets */
                        v += 2;
                        for (i = 0; i < sub; i++) {
                                seq_len <<= 8;
                                seq_len |= v[i];
                        }

                        if (seq_len != vlen - 2 - sub ||
                            v[sub] != SEQ_TAG_KEYID ||
                            v[sub + 1] > vlen - 4 - sub)
                                return -EBADMSG;

                        key_len = v[sub + 1];
                        v += (sub + 2);
                }

                f = kmalloc(key_len * 2 + 1, GFP_KERNEL);
                if (!f)
                        return -ENOMEM;
                for (i = 0; i < key_len; 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);
}