/* 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/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/oid_registry.h>
#include <crypto/public_key.h>
#include "x509_parser.h"
#include "x509.asn1.h"
#include "x509_akid.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 */
        unsigned        raw_akid_size;
        const void      *raw_akid;              /* Raw authorityKeyId in ASN.1 */
        const void      *akid_raw_issuer;       /* Raw directoryName in authorityKeyId */
        unsigned        akid_raw_issuer_size;
};

/*
 * Free an X.509 certificate
 */
void x509_free_certificate(struct x509_certificate *cert)
{
        if (cert) {
                public_key_free(cert->pub);
                public_key_signature_free(cert->sig);
                kfree(cert->issuer);
                kfree(cert->subject);
                kfree(cert->id);
                kfree(cert->skid);
                kfree(cert);
        }
}
EXPORT_SYMBOL_GPL(x509_free_certificate);

/*
 * 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;
        struct asymmetric_key_id *kid;
        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;
        cert->sig = kzalloc(sizeof(struct public_key_signature), GFP_KERNEL);
        if (!cert->sig)
                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 AuthorityKeyIdentifier */
        if (ctx->raw_akid) {
                pr_devel("AKID: %u %*phN\n",
                         ctx->raw_akid_size, ctx->raw_akid_size, ctx->raw_akid);
                ret = asn1_ber_decoder(&x509_akid_decoder, ctx,
                                       ctx->raw_akid, ctx->raw_akid_size);
                if (ret < 0) {
                        pr_warn("Couldn't decode AuthKeyIdentifier\n");
                        goto error_decode;
                }
        }

        ret = -ENOMEM;
        cert->pub->key = kmemdup(ctx->key, ctx->key_size, GFP_KERNEL);
        if (!cert->pub->key)
                goto error_decode;

        cert->pub->keylen = ctx->key_size;

        /* Grab the signature bits */
        ret = x509_get_sig_params(cert);
        if (ret < 0)
                goto error_decode;

        /* Generate cert issuer + serial number key ID */
        kid = asymmetric_key_generate_id(cert->raw_serial,
                                         cert->raw_serial_size,
                                         cert->raw_issuer,
                                         cert->raw_issuer_size);
        if (IS_ERR(kid)) {
                ret = PTR_ERR(kid);
                goto error_decode;
        }
        cert->id = kid;

        /* Detect self-signed certificates */
        ret = x509_check_for_self_signed(cert);
        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);
}
EXPORT_SYMBOL_GPL(x509_cert_parse);

/*
 * 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 = "md4";
                goto rsa_pkcs1;

        case OID_sha1WithRSAEncryption:
                ctx->cert->sig->hash_algo = "sha1";
                goto rsa_pkcs1;

        case OID_sha256WithRSAEncryption:
                ctx->cert->sig->hash_algo = "sha256";
                goto rsa_pkcs1;

        case OID_sha384WithRSAEncryption:
                ctx->cert->sig->hash_algo = "sha384";
                goto rsa_pkcs1;

        case OID_sha512WithRSAEncryption:
                ctx->cert->sig->hash_algo = "sha512";
                goto rsa_pkcs1;

        case OID_sha224WithRSAEncryption:
                ctx->cert->sig->hash_algo = "sha224";
                goto rsa_pkcs1;
        }

rsa_pkcs1:
        ctx->cert->sig->pkey_algo = "rsa";
        ctx->cert->sig->encoding = "pkcs1";
        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;
        }

        if (strcmp(ctx->cert->sig->pkey_algo, "rsa") == 0) {
                /* Discard the BIT STRING metadata */
                if (vlen < 1 || *(const u8 *)value != 0)
                        return -EBADMSG;

                value++;
                vlen--;
        }

        ctx->cert->raw_sig = value;
        ctx->cert->raw_sig_size = vlen;
        return 0;
}

/*
 * Note the certificate serial number
 */
int x509_note_serial(void *context, size_t hdrlen,
                     unsigned char tag,
                     const void *value, size_t vlen)
{
        struct x509_parse_context *ctx = context;
        ctx->cert->raw_serial = value;
        ctx->cert->raw_serial_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;
        ctx->cert->raw_issuer = value;
        ctx->cert->raw_issuer_size = vlen;
        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;
        ctx->cert->raw_subject = value;
        ctx->cert->raw_subject_size = vlen;
        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;

        ctx->cert->pub->pkey_algo = "rsa";

        /* Discard the BIT STRING metadata */
        if (vlen < 1 || *(const u8 *)value != 0)
                return -EBADMSG;
        ctx->key = value + 1;
        ctx->key_size = vlen - 1;
        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;
        struct asymmetric_key_id *kid;
        const unsigned char *v = value;

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

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

                ctx->cert->raw_skid_size = vlen;
                ctx->cert->raw_skid = v;
                kid = asymmetric_key_generate_id(v, vlen, "", 0);
                if (IS_ERR(kid))
                        return PTR_ERR(kid);
                ctx->cert->skid = kid;
                pr_debug("subjkeyid %*phN\n", kid->len, kid->data);
                return 0;
        }

        if (ctx->last_oid == OID_authorityKeyIdentifier) {
                /* Get hold of the CA key fingerprint */
                ctx->raw_akid = v;
                ctx->raw_akid_size = vlen;
                return 0;
        }

        return 0;
}

/**
 * x509_decode_time - Decode an X.509 time ASN.1 object
 * @_t: The time to fill in
 * @hdrlen: The length of the object header
 * @tag: The object tag
 * @value: The object value
 * @vlen: The size of the object value
 *
 * Decode an ASN.1 universal time or generalised time field into a struct the
 * kernel can handle and check it for validity.  The time is decoded thus:
 *
 *      [RFC5280 §4.1.2.5]
 *      CAs conforming to this profile MUST always encode certificate validity
 *      dates through the year 2049 as UTCTime; certificate validity dates in
 *      2050 or later MUST be encoded as GeneralizedTime.  Conforming
 *      applications MUST be able to process validity dates that are encoded in
 *      either UTCTime or GeneralizedTime.
 */
int x509_decode_time(time64_t *_t,  size_t hdrlen,
                     unsigned char tag,
                     const unsigned char *value, size_t vlen)
{
        static const unsigned char month_lengths[] = { 31, 28, 31, 30, 31, 30,
                                                       31, 31, 30, 31, 30, 31 };
        const unsigned char *p = value;
        unsigned year, mon, day, hour, min, sec, mon_len;

#define dec2bin(X) ({ unsigned char x = (X) - '0'; if (x > 9) goto invalid_time; x; })
#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;
                year = DD2bin(p);
                if (year >= 50)
                        year += 1900;
                else
                        year += 2000;
        } else if (tag == ASN1_GENTIM) {
                /* GenTime: YYYYMMDDHHMMSSZ */
                if (vlen != 15)
                        goto unsupported_time;
                year = DD2bin(p) * 100 + DD2bin(p);
                if (year >= 1950 && year <= 2049)
                        goto invalid_time;
        } else {
                goto unsupported_time;
        }

        mon  = DD2bin(p);
        day = DD2bin(p);
        hour = DD2bin(p);
        min  = DD2bin(p);
        sec  = DD2bin(p);

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

        if (year < 1970 ||
            mon < 1 || mon > 12)
                goto invalid_time;

        mon_len = month_lengths[mon - 1];
        if (mon == 2) {
                if (year % 4 == 0) {
                        mon_len = 29;
                        if (year % 100 == 0) {
                                mon_len = 28;
                                if (year % 400 == 0)
                                        mon_len = 29;
                        }
                }
        }

        if (day < 1 || day > mon_len ||
            hour > 24 || /* ISO 8601 permits 24:00:00 as midnight tomorrow */
            min > 59 ||
            sec > 60) /* ISO 8601 permits leap seconds [X.680 46.3] */
                goto invalid_time;

        *_t = mktime64(year, mon, day, hour, min, sec);
        return 0;

unsupported_time:
        pr_debug("Got unsupported time [tag %02x]: '%*phN'\n",
                 tag, (int)vlen, value);
        return -EBADMSG;
invalid_time:
        pr_debug("Got invalid time [tag %02x]: '%*phN'\n",
                 tag, (int)vlen, value);
        return -EBADMSG;
}
EXPORT_SYMBOL_GPL(x509_decode_time);

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_decode_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_decode_time(&ctx->cert->valid_to, hdrlen, tag, value, vlen);
}

/*
 * Note a key identifier-based AuthorityKeyIdentifier
 */
int x509_akid_note_kid(void *context, size_t hdrlen,
                       unsigned char tag,
                       const void *value, size_t vlen)
{
        struct x509_parse_context *ctx = context;
        struct asymmetric_key_id *kid;

        pr_debug("AKID: keyid: %*phN\n", (int)vlen, value);

        if (ctx->cert->sig->auth_ids[1])
                return 0;

        kid = asymmetric_key_generate_id(value, vlen, "", 0);
        if (IS_ERR(kid))
                return PTR_ERR(kid);
        pr_debug("authkeyid %*phN\n", kid->len, kid->data);
        ctx->cert->sig->auth_ids[1] = kid;
        return 0;
}

/*
 * Note a directoryName in an AuthorityKeyIdentifier
 */
int x509_akid_note_name(void *context, size_t hdrlen,
                        unsigned char tag,
                        const void *value, size_t vlen)
{
        struct x509_parse_context *ctx = context;

        pr_debug("AKID: name: %*phN\n", (int)vlen, value);

        ctx->akid_raw_issuer = value;
        ctx->akid_raw_issuer_size = vlen;
        return 0;
}

/*
 * Note a serial number in an AuthorityKeyIdentifier
 */
int x509_akid_note_serial(void *context, size_t hdrlen,
                          unsigned char tag,
                          const void *value, size_t vlen)
{
        struct x509_parse_context *ctx = context;
        struct asymmetric_key_id *kid;

        pr_debug("AKID: serial: %*phN\n", (int)vlen, value);

        if (!ctx->akid_raw_issuer || ctx->cert->sig->auth_ids[0])
                return 0;

        kid = asymmetric_key_generate_id(value,
                                         vlen,
                                         ctx->akid_raw_issuer,
                                         ctx->akid_raw_issuer_size);
        if (IS_ERR(kid))
                return PTR_ERR(kid);

        pr_debug("authkeyid %*phN\n", kid->len, kid->data);
        ctx->cert->sig->auth_ids[0] = kid;
        return 0;
}