Framework to build dane support

[exim.git] / src / src / dane-openssl.c

#include <stdio.h>
#include <string.h>
#include <stdint.h>

#include <openssl/opensslv.h>
#include <openssl/err.h>
#include <openssl/crypto.h>
#include <openssl/safestack.h>
#include <openssl/objects.h>
#include <openssl/x509.h>
#include <openssl/x509v3.h>
#include <openssl/evp.h>

#if OPENSSL_VERSION_NUMBER < 0x1000000fL
#error "OpenSSL 1.0.0 or higher required"
#else

#include "danessl.h"

#define DANE_F_ADD_SKID                 100
#define DANE_F_CHECK_END_ENTITY         101
#define DANE_F_GROW_CHAIN               102
#define DANE_F_LIST_ALLOC               103
#define DANE_F_MATCH                    104
#define DANE_F_PUSH_EXT                 105
#define DANE_F_SET_TRUST_ANCHOR         106
#define DANE_F_SSL_CTX_DANE_INIT        107
#define DANE_F_SSL_DANE_ADD_TLSA        108
#define DANE_F_SSL_DANE_INIT            109
#define DANE_F_SSL_DANE_LIBRARY_INIT    110
#define DANE_F_VERIFY_CERT              111
#define DANE_F_WRAP_CERT                112

#define DANE_R_BAD_CERT                 100
#define DANE_R_BAD_CERT_PKEY            101
#define DANE_R_BAD_DATA_LENGTH          102
#define DANE_R_BAD_DIGEST               103
#define DANE_R_BAD_NULL_DATA            104
#define DANE_R_BAD_PKEY                 105
#define DANE_R_BAD_SELECTOR             106
#define DANE_R_BAD_USAGE                107
#define DANE_R_DANE_INIT                108
#define DANE_R_DANE_SUPPORT             109
#define DANE_R_LIBRARY_INIT             110
#define DANE_R_NOSIGN_KEY               111
#define DANE_R_SCTX_INIT                112

#ifndef OPENSSL_NO_ERR
#define DANE_F_PLACEHOLDER              0               /* FIRST! Value TBD */
static ERR_STRING_DATA dane_str_functs[] = {
    {DANE_F_PLACEHOLDER,                "DANE library"},        /* FIRST!!! */
    {DANE_F_ADD_SKID,                   "add_skid"},
    {DANE_F_CHECK_END_ENTITY,           "check_end_entity"},
    {DANE_F_GROW_CHAIN,                 "grow_chain"},
    {DANE_F_LIST_ALLOC,                 "list_alloc"},
    {DANE_F_MATCH,                      "match"},
    {DANE_F_PUSH_EXT,                   "push_ext"},
    {DANE_F_SET_TRUST_ANCHOR,           "set_trust_anchor"},
    {DANE_F_SSL_CTX_DANE_INIT,          "SSL_CTX_dane_init"},
    {DANE_F_SSL_DANE_ADD_TLSA,          "SSL_dane_add_tlsa"},
    {DANE_F_SSL_DANE_INIT,              "SSL_dane_init"},
    {DANE_F_SSL_DANE_LIBRARY_INIT,      "SSL_dane_library_init"},
    {DANE_F_VERIFY_CERT,                "verify_cert"},
    {DANE_F_WRAP_CERT,                  "wrap_cert"},
    {0,                                 NULL}
};
static ERR_STRING_DATA dane_str_reasons[] = {
    {DANE_R_BAD_CERT,           "Bad TLSA record certificate"},
    {DANE_R_BAD_CERT_PKEY,      "Bad TLSA record certificate public key"},
    {DANE_R_BAD_DATA_LENGTH,    "Bad TLSA record digest length"},
    {DANE_R_BAD_DIGEST,         "Bad TLSA record digest"},
    {DANE_R_BAD_NULL_DATA,      "Bad TLSA record null data"},
    {DANE_R_BAD_PKEY,           "Bad TLSA record public key"},
    {DANE_R_BAD_SELECTOR,       "Bad TLSA record selector"},
    {DANE_R_BAD_USAGE,          "Bad TLSA record usage"},
    {DANE_R_DANE_INIT,          "SSL_dane_init() required"},
    {DANE_R_DANE_SUPPORT,       "DANE library features not supported"},
    {DANE_R_LIBRARY_INIT,       "SSL_dane_library_init() required"},
    {DANE_R_SCTX_INIT,          "SSL_CTX_dane_init() required"},
    {DANE_R_NOSIGN_KEY,         "Certificate usage 2 requires EC support"},
    {0,                         NULL}
};
#endif

#define DANEerr(f, r) ERR_PUT_error(err_lib_dane, (f), (r), __FILE__, __LINE__)

static int err_lib_dane = -1;
static int dane_idx = -1;

#ifdef X509_V_FLAG_PARTIAL_CHAIN       /* OpenSSL >= 1.0.2 */
static int wrap_to_root = 0;
#else
static int wrap_to_root = 1;
#endif

static void (*cert_free)(void *) = (void (*)(void *)) X509_free;
static void (*pkey_free)(void *) = (void (*)(void *)) EVP_PKEY_free;

typedef struct dane_list {
    struct dane_list *next;
    void *value;
} *dane_list;

#define LINSERT(h, e) do { (e)->next = (h); (h) = (e); } while (0)

typedef struct DANE_HOST_LIST {
    struct DANE_HOST_LIST *next;
    char *value;
} *DANE_HOST_LIST;

typedef struct dane_data {
    size_t datalen;
    unsigned char data[0];
} *dane_data;

typedef struct DANE_DATA_LIST {
    struct DANE_DATA_LIST *next;
    dane_data value;
} *DANE_DATA_LIST;

typedef struct dane_mtype {
    int mdlen;
    const EVP_MD *md;
    DANE_DATA_LIST data;
} *dane_mtype;

typedef struct DANE_MTYPE_LIST {
    struct DANE_MTYPE_LIST *next;
    dane_mtype value;
} *DANE_MTYPE_LIST;

typedef struct dane_selector {
    uint8_t selector;
    DANE_MTYPE_LIST mtype;
} *dane_selector;

typedef struct DANE_SELECTOR_LIST {
    struct DANE_SELECTOR_LIST *next;
    dane_selector value;
} *DANE_SELECTOR_LIST;

typedef struct DANE_PKEY_LIST {
    struct DANE_PKEY_LIST *next;
    EVP_PKEY *value;
} *DANE_PKEY_LIST;

typedef struct DANE_CERT_LIST {
    struct DANE_CERT_LIST *next;
    X509 *value;
} *DANE_CERT_LIST;

typedef struct SSL_DANE {
    int            (*verify)(X509_STORE_CTX *);
    STACK_OF(X509) *roots;
    STACK_OF(X509) *chain;
    const char     *thost;              /* TLSA base domain */
    char           *mhost;              /* Matched, peer name */
    DANE_PKEY_LIST pkeys;
    DANE_CERT_LIST certs;
    DANE_HOST_LIST hosts;
    DANE_SELECTOR_LIST selectors[SSL_DANE_USAGE_LAST + 1];
    int            depth;
    int            multi;               /* Multi-label wildcards? */
    int            count;               /* Number of TLSA records */
} SSL_DANE;

#ifndef X509_V_ERR_HOSTNAME_MISMATCH
#define X509_V_ERR_HOSTNAME_MISMATCH X509_V_ERR_APPLICATION_VERIFICATION
#endif

static int match(DANE_SELECTOR_LIST slist, X509 *cert, int depth)
{
    int matched;

    /*
     * Note, set_trust_anchor() needs to know whether the match was for a
     * pkey digest or a certificate digest.  We return MATCHED_PKEY or
     * MATCHED_CERT accordingly.
     */
#define MATCHED_CERT (SSL_DANE_SELECTOR_CERT + 1)
#define MATCHED_PKEY (SSL_DANE_SELECTOR_SPKI + 1)

    /*
     * Loop over each selector, mtype, and associated data element looking
     * for a match.
     */
    for (matched = 0; !matched && slist; slist = slist->next) {
        DANE_MTYPE_LIST m;
        unsigned char mdbuf[EVP_MAX_MD_SIZE];
        unsigned char *buf;
        unsigned char *buf2;
        unsigned int len;

        /*
         * Extract ASN.1 DER form of certificate or public key.
         */
        switch (slist->value->selector) {
        case SSL_DANE_SELECTOR_CERT:
            len = i2d_X509(cert, NULL);
            buf2 = buf = (unsigned char *) OPENSSL_malloc(len);
            if (buf)
                i2d_X509(cert, &buf2);
            break;
        case SSL_DANE_SELECTOR_SPKI:
            len = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), NULL);
            buf2 = buf = (unsigned char *) OPENSSL_malloc(len);
            if (buf)
                i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), &buf2);
            break;
        }

        if (buf == NULL) {
            DANEerr(DANE_F_MATCH, ERR_R_MALLOC_FAILURE);
            return 0;
        }
        OPENSSL_assert(buf2 - buf == len);

        /*
         * Loop over each mtype and data element
         */
        for (m = slist->value->mtype; !matched && m; m = m->next) {
            DANE_DATA_LIST d;
            unsigned char *cmpbuf = buf;
            unsigned int cmplen = len;

            /*
             * If it is a digest, compute the corresponding digest of the
             * DER data for comparison, otherwise, use the full object.
             */
            if (m->value->md) {
                cmpbuf = mdbuf;
                if (!EVP_Digest(buf, len, cmpbuf, &cmplen, m->value->md, 0))
                    matched = -1;
            }
            for (d = m->value->data; !matched && d; d = d->next)
                if (cmplen == d->value->datalen &&
                    memcmp(cmpbuf, d->value->data, cmplen) == 0)
                    matched = slist->value->selector + 1;
        }

        OPENSSL_free(buf);
    }

    return matched;
}

static int push_ext(X509 *cert, X509_EXTENSION *ext)
{
    X509_EXTENSIONS *exts;

    if (ext) {
        if ((exts = cert->cert_info->extensions) == 0)
            exts = cert->cert_info->extensions = sk_X509_EXTENSION_new_null();
        if (exts && sk_X509_EXTENSION_push(exts, ext))
            return 1;
        X509_EXTENSION_free(ext);
    }
    DANEerr(DANE_F_PUSH_EXT, ERR_R_MALLOC_FAILURE);
    return 0;
}

static int add_ext(X509 *issuer, X509 *subject, int ext_nid, char *ext_val)
{
    X509V3_CTX v3ctx;

    X509V3_set_ctx(&v3ctx, issuer, subject, 0, 0, 0);
    return push_ext(subject, X509V3_EXT_conf_nid(0, &v3ctx, ext_nid, ext_val));
}

static int set_serial(X509 *cert, AUTHORITY_KEYID *akid, X509 *subject)
{
    int ret = 0;
    BIGNUM *bn;

    if (akid && akid->serial)
        return (X509_set_serialNumber(cert, akid->serial));

    /*
     * Add one to subject's serial to avoid collisions between TA serial and
     * serial of signing root.
     */
    if ((bn = ASN1_INTEGER_to_BN(X509_get_serialNumber(subject), 0)) != 0
        && BN_add_word(bn, 1)
        && BN_to_ASN1_INTEGER(bn, X509_get_serialNumber(cert)))
        ret = 1;

    if (bn)
        BN_free(bn);
    return ret;
}

static int add_akid(X509 *cert, AUTHORITY_KEYID *akid)
{
    int nid = NID_authority_key_identifier;
    ASN1_STRING *id;
    unsigned char c = 0;
    int ret = 0;

    /*
     * 0 will never be our subject keyid from a SHA-1 hash, but it could be
     * our subject keyid if forced from child's akid.  If so, set our
     * authority keyid to 1.  This way we are never self-signed, and thus
     * exempt from any potential (off by default for now in OpenSSL)
     * self-signature checks!
     */
    id = (ASN1_STRING *) ((akid && akid->keyid) ? akid->keyid : 0);
    if (id && M_ASN1_STRING_length(id) == 1 && *M_ASN1_STRING_data(id) == c)
        c = 1;

    if ((akid = AUTHORITY_KEYID_new()) != 0
        && (akid->keyid = ASN1_OCTET_STRING_new()) != 0
        && M_ASN1_OCTET_STRING_set(akid->keyid, (void *) &c, 1)
        && X509_add1_ext_i2d(cert, nid, akid, 0, X509V3_ADD_APPEND))
        ret = 1;
    if (akid)
        AUTHORITY_KEYID_free(akid);
    return ret;
}

static int add_skid(X509 *cert, AUTHORITY_KEYID *akid)
{
    int nid = NID_subject_key_identifier;

    if (!akid || !akid->keyid)
        return add_ext(0, cert, nid, "hash");
    return X509_add1_ext_i2d(cert, nid, akid->keyid, 0, X509V3_ADD_APPEND) > 0;
}

static X509_NAME *akid_issuer_name(AUTHORITY_KEYID *akid)
{
    if (akid && akid->issuer) {
        int     i;
        GENERAL_NAMES *gens = akid->issuer;

        for (i = 0; i < sk_GENERAL_NAME_num(gens); ++i) {
            GENERAL_NAME *gn = sk_GENERAL_NAME_value(gens, i);

            if (gn->type == GEN_DIRNAME)
                return (gn->d.dirn);
        }
    }
    return 0;
}

static int set_issuer_name(X509 *cert, AUTHORITY_KEYID *akid)
{
    X509_NAME *name = akid_issuer_name(akid);

    /*
     * If subject's akid specifies an authority key identifer issuer name, we
     * must use that.
     */
    if (name)
        return X509_set_issuer_name(cert, name);
    return X509_set_issuer_name(cert, X509_get_subject_name(cert));
}

static int grow_chain(SSL_DANE *dane, int trusted, X509 *cert)
{
    STACK_OF(X509) **xs = trusted ? &dane->roots : &dane->chain;
    static ASN1_OBJECT *serverAuth = 0;

#define UNTRUSTED 0
#define TRUSTED 1

    if (trusted && serverAuth == 0 &&
       (serverAuth = OBJ_nid2obj(NID_server_auth)) == 0) {
        DANEerr(DANE_F_GROW_CHAIN, ERR_R_MALLOC_FAILURE);
        return 0;
    }
    if (!*xs && (*xs = sk_X509_new_null()) == 0) {
        DANEerr(DANE_F_GROW_CHAIN, ERR_R_MALLOC_FAILURE);
        return 0;
    }

    if (cert) {
        if (trusted && !X509_add1_trust_object(cert, serverAuth))
            return 0;
        CRYPTO_add(&cert->references, 1, CRYPTO_LOCK_X509);
        if (!sk_X509_push(*xs, cert)) {
            X509_free(cert);
            DANEerr(DANE_F_GROW_CHAIN, ERR_R_MALLOC_FAILURE);
            return 0;
        }
    }
    return 1;
}

static int wrap_issuer(
        SSL_DANE *dane,
        EVP_PKEY *key,
        X509 *subject,
        int depth,
        int top
)
{
    int ret = 1;
    X509 *cert = 0;
    AUTHORITY_KEYID *akid;
    X509_NAME *name = X509_get_issuer_name(subject);
    EVP_PKEY *newkey = key ? key : X509_get_pubkey(subject);

#define WRAP_MID 0              /* Ensure intermediate. */
#define WRAP_TOP 1              /* Ensure self-signed. */

    if (name == 0 || newkey == 0 || (cert = X509_new()) == 0)
        return 0;

    /*
     * Record the depth of the trust-anchor certificate.
     */
    if (dane->depth < 0)
        dane->depth = depth + 1;

    /*
     * XXX: Uncaught error condition:
     *
     * The return value is NULL both when the extension is missing, and when
     * OpenSSL rans out of memory while parsing the extension.
     */
    ERR_clear_error();
    akid = X509_get_ext_d2i(subject, NID_authority_key_identifier, 0, 0);
    /* XXX: Should we peek at the error stack here??? */

    /*
     * If top is true generate a self-issued root CA, otherwise an
     * intermediate CA and possibly its self-signed issuer.
     *
     * CA cert valid for +/- 30 days
     */
    if (!X509_set_version(cert, 2)
        || !set_serial(cert, akid, subject)
        || !X509_set_subject_name(cert, name)
        || !set_issuer_name(cert, akid)
        || !X509_gmtime_adj(X509_get_notBefore(cert), -30 * 86400L)
        || !X509_gmtime_adj(X509_get_notAfter(cert), 30 * 86400L)
        || !X509_set_pubkey(cert, newkey)
        || !add_ext(0, cert, NID_basic_constraints, "CA:TRUE")
        || (!top && !add_akid(cert, akid))
        || !add_skid(cert, akid)
        || (!top && wrap_to_root &&
            !wrap_issuer(dane, newkey, cert, depth, WRAP_TOP))) {
        ret = 0;
    }
    if (akid)
        AUTHORITY_KEYID_free(akid);
    if (!key)
        EVP_PKEY_free(newkey);
    if (ret) {
        if (!top && wrap_to_root)
            ret = grow_chain(dane, UNTRUSTED, cert);
        else
            ret = grow_chain(dane, TRUSTED, cert);
    }
    if (cert)
        X509_free(cert);
    return ret;
}

static int wrap_cert(SSL_DANE *dane, X509 *tacert, int depth)
{
    if (dane->depth < 0)
        dane->depth = depth + 1;

    /*
     * If the TA certificate is self-issued, or need not be, use it directly.
     * Otherwise, synthesize requisuite ancestors.
     */
    if (!wrap_to_root
        || X509_check_issued(tacert, tacert) == X509_V_OK)
        return grow_chain(dane, TRUSTED, tacert);

    if (wrap_issuer(dane, 0, tacert, depth, WRAP_MID))
        return grow_chain(dane, UNTRUSTED, tacert);
    return 0;
}

static int ta_signed(SSL_DANE *dane, X509 *cert, int depth)
{
    DANE_CERT_LIST x;
    DANE_PKEY_LIST k;
    EVP_PKEY *pk;
    int done = 0;

    /*
     * First check whether issued and signed by a TA cert, this is cheaper
     * than the bare-public key checks below, since we can determine whether
     * the candidate TA certificate issued the certificate to be checked
     * first (name comparisons), before we bother with signature checks
     * (public key operations).
     */
    for (x = dane->certs; !done && x; x = x->next) {
        if (X509_check_issued(x->value, cert) == X509_V_OK) {
            if ((pk = X509_get_pubkey(x->value)) == 0) {
                /*
                 * The cert originally contained a valid pkey, which does
                 * not just vanish, so this is most likely a memory error.
                 */
                done = -1;
                break;
            }
            /* Check signature, since some other TA may work if not this. */
            if (X509_verify(cert, pk) > 0)
                done = wrap_cert(dane, x->value, depth) ? 1 : -1;
            EVP_PKEY_free(pk);
        }
    }

    /*
     * With bare TA public keys, we can't check whether the trust chain is
     * issued by the key, but we can determine whether it is signed by the
     * key, so we go with that.
     *
     * Ideally, the corresponding certificate was presented in the chain, and we
     * matched it by its public key digest one level up.  This code is here
     * to handle adverse conditions imposed by sloppy administrators of
     * receiving systems with poorly constructed chains.
     *
     * We'd like to optimize out keys that should not match when the cert's
     * authority key id does not match the key id of this key computed via
     * the RFC keyid algorithm (SHA-1 digest of public key bit-string sans
     * ASN1 tag and length thus also excluding the unused bits field that is
     * logically part of the length).  However, some CAs have a non-standard
     * authority keyid, so we lose.  Too bad.
     *
     * This may push errors onto the stack when the certificate signature is
     * not of the right type or length, throw these away,
     */
    for (k = dane->pkeys; !done && k; k = k->next)
        if (X509_verify(cert, k->value) > 0)
            done = wrap_issuer(dane, k->value, cert, depth, WRAP_MID) ? 1 : -1;
        else
            ERR_clear_error();

    return done;
}

static int set_trust_anchor(X509_STORE_CTX *ctx, SSL_DANE *dane, X509 *cert)
{
    int matched = 0;
    int n;
    int i;
    int depth = 0;
    EVP_PKEY *takey;
    X509 *ca;
    STACK_OF(X509) *in = ctx->untrusted;        /* XXX: Accessor? */

    if (!grow_chain(dane, UNTRUSTED, 0))
        return -1;

    /*
     * Accept a degenerate case: depth 0 self-signed trust-anchor.
     */
    if (X509_check_issued(cert, cert) == X509_V_OK) {
        dane->depth = 0;
        matched = match(dane->selectors[SSL_DANE_USAGE_TRUSTED_CA], cert, 0);
        if (matched > 0 && !grow_chain(dane, TRUSTED, cert))
            matched = -1;
        return matched;
    }

    /* Make a shallow copy of the input untrusted chain. */
    if ((in = sk_X509_dup(in)) == 0) {
        DANEerr(DANE_F_SET_TRUST_ANCHOR, ERR_R_MALLOC_FAILURE);
        return -1;
    }

    /*
     * At each iteration we consume the issuer of the current cert.  This
     * reduces the length of the "in" chain by one.  If no issuer is found,
     * we are done.  We also stop when a certificate matches a TA in the
     * peer's TLSA RRset.
     *
     * Caller ensures that the initial certificate is not self-signed.
     */
    for (n = sk_X509_num(in); n > 0; --n, ++depth) {
        for (i = 0; i < n; ++i)
            if (X509_check_issued(sk_X509_value(in, i), cert) == X509_V_OK)
                break;

        /*
         * Final untrusted element with no issuer in the peer's chain, it may
         * however be signed by a pkey or cert obtained via a TLSA RR.
         */
        if (i == n)
            break;

        /* Peer's chain contains an issuer ca. */
        ca = sk_X509_delete(in, i);

        /* If not a trust anchor, record untrusted ca and continue. */
        if ((matched = match(dane->selectors[SSL_DANE_USAGE_TRUSTED_CA], ca,
                             depth + 1)) == 0) {
            if (grow_chain(dane, UNTRUSTED, ca)) {
                if (!X509_check_issued(ca, ca) == X509_V_OK) {
                    /* Restart with issuer as subject */
                    cert = ca;
                    continue;
                }
                /* Final self-signed element, skip ta_signed() check. */
                cert = 0;
            } else
                matched = -1;
        } else if (matched == MATCHED_CERT) {
            if (!wrap_cert(dane, ca, depth))
                matched = -1;
        } else if (matched == MATCHED_PKEY) {
            if ((takey = X509_get_pubkey(ca)) == 0 ||
                !wrap_issuer(dane, takey, cert, depth, WRAP_MID)) {
                if (takey)
                    EVP_PKEY_free(takey);
                else
                    DANEerr(DANE_F_SET_TRUST_ANCHOR, ERR_R_MALLOC_FAILURE);
                matched = -1;
            }
        }
        break;
    }

    /* Shallow free the duplicated input untrusted chain. */
    sk_X509_free(in);

    /*
     * When the loop exits, if "cert" is set, it is not self-signed and has
     * no issuer in the chain, we check for a possible signature via a DNS
     * obtained TA cert or public key.
     */
    if (matched == 0 && cert)
         matched = ta_signed(dane, cert, depth);

    return matched;
}

static int check_end_entity(X509_STORE_CTX *ctx, SSL_DANE *dane, X509 *cert)
{
    int matched;

    matched = match(dane->selectors[SSL_DANE_USAGE_FIXED_LEAF], cert, 0);
    if (matched > 0) {
        if (ctx->chain == 0) {
            if ((ctx->chain = sk_X509_new_null()) != 0 &&
                sk_X509_push(ctx->chain, cert)) {
                CRYPTO_add(&cert->references, 1, CRYPTO_LOCK_X509);
            } else {
                DANEerr(DANE_F_CHECK_END_ENTITY, ERR_R_MALLOC_FAILURE);
                return -1;
            }
        }
    }
    return matched;
}

static int match_name(const char *certid, SSL_DANE *dane)
{
    int multi = dane->multi;
    DANE_HOST_LIST hosts = dane->hosts;

    for (/* NOP */; hosts; hosts = hosts->next) {
        int match_subdomain = 0;
        const char *domain = hosts->value;
        const char *parent;
        int idlen;
        int domlen;

        if (*domain == '.' && domain[1] != '\0') {
            ++domain;
            match_subdomain = 1;
        }

        /*
         * Sub-domain match: certid is any sub-domain of hostname.
         */
        if (match_subdomain) {
            if ((idlen = strlen(certid)) > (domlen = strlen(domain)) + 1
                && certid[idlen - domlen - 1] == '.'
                && !strcasecmp(certid + (idlen - domlen), domain))
                return 1;
            else
                continue;
        }

        /*
         * Exact match and initial "*" match. The initial "*" in a certid
         * matches one (if multi is false) or more hostname components under
         * the condition that the certid contains multiple hostname components.
         */
        if (!strcasecmp(certid, domain)
            || (certid[0] == '*' && certid[1] == '.' && certid[2] != 0
                && (parent = strchr(domain, '.')) != 0
                && (idlen = strlen(certid + 1)) <= (domlen = strlen(parent))
                && strcasecmp(multi ? parent + domlen - idlen : parent,
                              certid + 1) == 0))
            return 1;
    }
    return 0;
}

static char *check_name(char *name, int len)
{
    register char *cp = name + len;

    while (len > 0 && *--cp == 0)
        --len;                          /* Ignore trailing NULs */
    if (len <= 0)
        return 0;
    for (cp = name; *cp; cp++) {
        register char c = *cp;
        if (!((c >= 'a' && c <= 'z') ||
              (c >= '0' && c <= '9') ||
              (c >= 'A' && c <= 'Z') ||
              (c == '.' || c == '-') ||
              (c == '*')))
            return 0;                   /* Only LDH, '.' and '*' */
    }
    if (cp - name != len)               /* Guard against internal NULs */
        return 0;
    return name;
}

static char *parse_dns_name(const GENERAL_NAME *gn)
{
    if (gn->type != GEN_DNS)
        return 0;
    if (ASN1_STRING_type(gn->d.ia5) != V_ASN1_IA5STRING)
        return 0;
    return check_name((char *) ASN1_STRING_data(gn->d.ia5),
                      ASN1_STRING_length(gn->d.ia5));
}

static char *parse_subject_name(X509 *cert)
{
    X509_NAME *name = X509_get_subject_name(cert);
    X509_NAME_ENTRY *entry;
    ASN1_STRING *entry_str;
    unsigned char *namebuf;
    int nid = NID_commonName;
    int len;
    int i;

    if (name == 0 || (i = X509_NAME_get_index_by_NID(name, nid, -1)) < 0)
        return 0;
    if ((entry = X509_NAME_get_entry(name, i)) == 0)
        return 0;
    if ((entry_str = X509_NAME_ENTRY_get_data(entry)) == 0)
        return 0;

    if ((len = ASN1_STRING_to_UTF8(&namebuf, entry_str)) < 0)
        return 0;
    if (len <= 0 || check_name((char *) namebuf, len) == 0) {
        OPENSSL_free(namebuf);
        return 0;
    }
    return (char *) namebuf;
}

static int name_check(SSL_DANE *dane, X509 *cert)
{
    int matched = 0;
    int got_altname = 0;
    GENERAL_NAMES *gens;

    gens = X509_get_ext_d2i(cert, NID_subject_alt_name, 0, 0);
    if (gens) {
        int n = sk_GENERAL_NAME_num(gens);
        int i;

        for (i = 0; i < n; ++i) {
            const GENERAL_NAME *gn = sk_GENERAL_NAME_value(gens, i);
            const char *certid;

            if (gn->type != GEN_DNS)
                continue;
            got_altname = 1;
            certid = parse_dns_name(gn);
            if (certid && *certid) {
                if ((matched = match_name(certid, dane)) == 0)
                    continue;
                if ((dane->mhost = OPENSSL_strdup(certid)) == 0)
                    matched = -1;
                break;
            }
        }
        GENERAL_NAMES_free(gens);
    }

    /*
     * XXX: Should the subjectName be skipped when *any* altnames are present,
     * or only when DNS altnames are present?
     */
    if (got_altname == 0) {
        char *certid = parse_subject_name(cert);
        if (certid != 0 && *certid && (matched = match_name(certid, dane)) != 0)
            dane->mhost = certid;       /* Already a copy */
    }
    return matched;
}

static int verify_chain(X509_STORE_CTX *ctx)
{
    DANE_SELECTOR_LIST issuer_rrs;
    DANE_SELECTOR_LIST leaf_rrs;
    int (*cb)(int, X509_STORE_CTX *) = ctx->verify_cb;
    int ssl_idx = SSL_get_ex_data_X509_STORE_CTX_idx();
    SSL *ssl = X509_STORE_CTX_get_ex_data(ctx, ssl_idx);
    SSL_DANE *dane = SSL_get_ex_data(ssl, dane_idx);
    X509 *cert = ctx->cert;             /* XXX: accessor? */
    int matched = 0;
    int chain_length = sk_X509_num(ctx->chain);

    issuer_rrs = dane->selectors[SSL_DANE_USAGE_LIMIT_ISSUER];
    leaf_rrs = dane->selectors[SSL_DANE_USAGE_LIMIT_LEAF];
    ctx->verify = dane->verify;

    if ((matched = name_check(dane, cert)) < 0) {
        X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
        return 0;
    }

    if (!matched) {
        ctx->error_depth = 0;
        ctx->current_cert = cert;
        X509_STORE_CTX_set_error(ctx, X509_V_ERR_HOSTNAME_MISMATCH);
        if (!cb(0, ctx))
            return 0;
    }
    matched = 0;

    /*
     * Satisfy at least one usage 0 or 1 constraint, unless we've already
     * matched a usage 2 trust anchor.
     *
     * XXX: internal_verify() doesn't callback with top certs that are not
     * self-issued.  This should be fixed in a future OpenSSL.
     */
    if (dane->roots && sk_X509_num(dane->roots)) {
#ifndef NO_CALLBACK_WORKAROUND
        X509 *top = sk_X509_value(ctx->chain, dane->depth);

        if (X509_check_issued(top, top) != X509_V_OK) {
            ctx->error_depth = dane->depth;
            ctx->current_cert = top;
            if (!cb(1, ctx))
                return 0;
        }
#endif
        /* Pop synthetic trust-anchor ancestors off the chain! */
        while (--chain_length > dane->depth)
            X509_free(sk_X509_pop(ctx->chain));
    } else if (issuer_rrs || leaf_rrs) {
        int n = chain_length;

        /*
         * Check for an EE match, then a CA match at depths > 0, and
         * finally, if the EE cert is self-issued, for a depth 0 CA match.
         */
        if (leaf_rrs)
            matched = match(leaf_rrs, cert, 0);
        while (!matched && issuer_rrs && --n >= 0) {
            X509 *xn = sk_X509_value(ctx->chain, n);

            if (n > 0 || X509_check_issued(xn, xn) == X509_V_OK)
                matched = match(issuer_rrs, xn, n);
        }

        if (matched < 0) {
            X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
            return 0;
        }

        if (!matched) {
            ctx->current_cert = cert;
            ctx->error_depth = 0;
            X509_STORE_CTX_set_error(ctx, X509_V_ERR_CERT_UNTRUSTED);
            if (!cb(0, ctx))
                return 0;
        }
    }

    return ctx->verify(ctx);
}

static int verify_cert(X509_STORE_CTX *ctx, void *unused_ctx)
{
    static int ssl_idx = -1;
    SSL *ssl;
    SSL_DANE *dane;
    int (*cb)(int, X509_STORE_CTX *) = ctx->verify_cb;
    int matched;
    X509 *cert = ctx->cert;             /* XXX: accessor? */

    if (ssl_idx < 0)
        ssl_idx = SSL_get_ex_data_X509_STORE_CTX_idx();
    if (dane_idx < 0) {
        DANEerr(DANE_F_VERIFY_CERT, ERR_R_MALLOC_FAILURE);
        return -1;
    }

    ssl = X509_STORE_CTX_get_ex_data(ctx, ssl_idx);
    if ((dane = SSL_get_ex_data(ssl, dane_idx)) == 0 || cert == 0)
        return X509_verify_cert(ctx);

    if (dane->selectors[SSL_DANE_USAGE_FIXED_LEAF]) {
        if ((matched = check_end_entity(ctx, dane, cert)) > 0) {
            ctx->error_depth = 0;
            ctx->current_cert = cert;
            return cb(1, ctx);
        }
        if (matched < 0) {
            X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
            return -1;
        }
    }

    if (dane->selectors[SSL_DANE_USAGE_TRUSTED_CA]) {
        if ((matched = set_trust_anchor(ctx, dane, cert)) < 0) {
            X509_STORE_CTX_set_error(ctx, X509_V_ERR_OUT_OF_MEM);
            return -1;
        }
        if (matched) {
            /*
             * Check that setting the untrusted chain updates the expected
             * structure member at the expected offset.
             */
            X509_STORE_CTX_trusted_stack(ctx, dane->roots);
            X509_STORE_CTX_set_chain(ctx, dane->chain);
            OPENSSL_assert(ctx->untrusted == dane->chain);
        }
    }

    /*
     * Name checks and usage 0/1 constraint enforcement are delayed until
     * X509_verify_cert() builds the full chain and calls our verify_chain()
     * wrapper.
     */
    dane->verify = ctx->verify;
    ctx->verify = verify_chain;

    return X509_verify_cert(ctx);
}

static dane_list list_alloc(size_t vsize)
{
    void *value = (void *) OPENSSL_malloc(vsize);
    dane_list l;

    if (value == 0) {
        DANEerr(DANE_F_LIST_ALLOC, ERR_R_MALLOC_FAILURE);
        return 0;
    }
    if ((l = (dane_list) OPENSSL_malloc(sizeof(*l))) == 0) {
        OPENSSL_free(value);
        DANEerr(DANE_F_LIST_ALLOC, ERR_R_MALLOC_FAILURE);
        return 0;
    }
    l->next = 0;
    l->value = value;
    return l;
}

static void list_free(void *list, void (*f)(void *))
{
    dane_list head = (dane_list) list;
    dane_list next;

    for (/* NOP */; head; head = next) {
        next = head->next;
        if (f && head->value)
            f(head->value);
        OPENSSL_free(head);
    }
}

static void dane_mtype_free(void *p)
{
    list_free(((dane_mtype) p)->data, OPENSSL_freeFunc);
    OPENSSL_free(p);
}

static void dane_selector_free(void *p)
{
    list_free(((dane_selector) p)->mtype, dane_mtype_free);
    OPENSSL_free(p);
}

void DANESSL_cleanup(SSL *ssl)
{
    SSL_DANE *dane;
    int u;

    if (dane_idx < 0 || (dane = SSL_get_ex_data(ssl, dane_idx)) == 0)
        return;
    (void) SSL_set_ex_data(ssl, dane_idx, 0);

    if (dane->hosts)
        list_free(dane->hosts, OPENSSL_freeFunc);
    if (dane->mhost)
        OPENSSL_free(dane->mhost);
    for (u = 0; u <= SSL_DANE_USAGE_LAST; ++u)
        if (dane->selectors[u])
            list_free(dane->selectors[u], dane_selector_free);
    if (dane->pkeys)
        list_free(dane->pkeys, pkey_free);
    if (dane->certs)
        list_free(dane->certs, cert_free);
    if (dane->roots)
        sk_X509_pop_free(dane->roots, X509_free);
    if (dane->chain)
        sk_X509_pop_free(dane->chain, X509_free);
    OPENSSL_free(dane);
}

static DANE_HOST_LIST host_list_init(const char **src)
{
    DANE_HOST_LIST head = 0;

    while (*src) {
        DANE_HOST_LIST elem = (DANE_HOST_LIST) OPENSSL_malloc(sizeof(*elem));
        if (elem == 0) {
            list_free(head, OPENSSL_freeFunc);
            return 0;
        }
        elem->value = OPENSSL_strdup(*src++);
        LINSERT(head, elem);
    }
    return head;
}

int DANESSL_add_tlsa(
        SSL *ssl,
        uint8_t usage,
        uint8_t selector,
        const char *mdname,
        unsigned const char *data,
        size_t dlen
)
{
    SSL_DANE *dane;
    DANE_SELECTOR_LIST s = 0;
    DANE_MTYPE_LIST m = 0;
    DANE_DATA_LIST d = 0;
    DANE_CERT_LIST xlist = 0;
    DANE_PKEY_LIST klist = 0;
    const EVP_MD *md = 0;

    if (dane_idx < 0 || (dane = SSL_get_ex_data(ssl, dane_idx)) == 0) {
        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_DANE_INIT);
        return -1;
    }

    if (usage > SSL_DANE_USAGE_LAST) {
        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_USAGE);
        return 0;
    }
    if (selector > SSL_DANE_SELECTOR_LAST) {
        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_SELECTOR);
        return 0;
    }
    if (mdname && (md = EVP_get_digestbyname(mdname)) == 0) {
        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_DIGEST);
        return 0;
    }
    if (!data) {
        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_NULL_DATA);
        return 0;
    }
    if (mdname && dlen != EVP_MD_size(md)) {
        DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_DATA_LENGTH);
        return 0;
    }

    if (mdname == 0) {
        X509 *x = 0;
        EVP_PKEY *k = 0;
        const unsigned char *p = data;

#define xklistinit(lvar, ltype, var, freeFunc) do { \
            (lvar) = (ltype) OPENSSL_malloc(sizeof(*(lvar))); \
            if ((lvar) == 0) { \
                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, ERR_R_MALLOC_FAILURE); \
                freeFunc((var)); \
                return 0; \
            } \
            (lvar)->next = 0; \
            lvar->value = var; \
        } while (0)
#define xkfreeret(ret) do { \
            if (xlist) list_free(xlist, cert_free); \
            if (klist) list_free(klist, pkey_free); \
            return (ret); \
        } while (0)

        switch (selector) {
        case SSL_DANE_SELECTOR_CERT:
            if (!d2i_X509(&x, &p, dlen) || dlen != p - data) {
                if (x)
                    X509_free(x);
                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_CERT);
                return 0;
            }
            k = X509_get_pubkey(x);
            EVP_PKEY_free(k);
            if (k == 0) {
                X509_free(x);
                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_CERT_PKEY);
                return 0;
            }
            if (usage == SSL_DANE_USAGE_TRUSTED_CA)
                xklistinit(xlist, DANE_CERT_LIST, x, X509_free);
            break;

        case SSL_DANE_SELECTOR_SPKI:
            if (!d2i_PUBKEY(&k, &p, dlen) || dlen != p - data) {
                if (k)
                    EVP_PKEY_free(k);
                DANEerr(DANE_F_SSL_DANE_ADD_TLSA, DANE_R_BAD_PKEY);
                return 0;
            }
            if (usage == SSL_DANE_USAGE_TRUSTED_CA)
                xklistinit(klist, DANE_PKEY_LIST, k, EVP_PKEY_free);
            break;
        }
    }

    /* Find insertion point and don't add duplicate elements. */
    for (s = dane->selectors[usage]; s; s = s->next)
        if (s->value->selector == selector)
            for (m = s->value->mtype; m; m = m->next)
                if (m->value->md == md)
                    for (d = m->value->data; d; d = d->next)
                        if (d->value->datalen == dlen &&
                            memcmp(d->value->data, data, dlen) == 0)
                            xkfreeret(1);

    if ((d = (DANE_DATA_LIST) list_alloc(sizeof(*d->value) + dlen)) == 0)
        xkfreeret(0);
    d->value->datalen = dlen;
    memcpy(d->value->data, data, dlen);
    if (!m) {
        if ((m = (DANE_MTYPE_LIST) list_alloc(sizeof(*m->value))) == 0) {
            list_free(d, OPENSSL_freeFunc);
            xkfreeret(0);
        }
        m->value->data = 0;
        if ((m->value->md = md) != 0)
            m->value->mdlen = dlen;
        if (!s) {
            if ((s = (DANE_SELECTOR_LIST) list_alloc(sizeof(*s->value))) == 0) {
                list_free(m, dane_mtype_free);
                xkfreeret(0);
            }
            s->value->mtype = 0;
            s->value->selector = selector;
            LINSERT(dane->selectors[usage], s);
        }
        LINSERT(s->value->mtype, m);
    }
    LINSERT(m->value->data, d);

    if (xlist)
        LINSERT(dane->certs, xlist);
    else if (klist)
        LINSERT(dane->pkeys, klist);
    ++dane->count;
    return 1;
}

int DANESSL_init(SSL *ssl, const char *sni_domain, const char **hostnames)
{
    SSL_DANE *dane;
    int i;
#ifdef OPENSSL_INTERNAL
    SSL_CTX *sctx = SSL_get_SSL_CTX(ssl);

    if (sctx->app_verify_callback != verify_cert) {
        DANEerr(DANE_F_SSL_DANE_INIT, DANE_R_SCTX_INIT);
        return -1;
    }
#else
    if (dane_idx < 0) {
        DANEerr(DANE_F_SSL_DANE_INIT, DANE_R_LIBRARY_INIT);
        return -1;
    }
#endif

    if (sni_domain && !SSL_set_tlsext_host_name(ssl, sni_domain))
        return 0;

    if ((dane = (SSL_DANE *) OPENSSL_malloc(sizeof(SSL_DANE))) == 0) {
        DANEerr(DANE_F_SSL_DANE_INIT, ERR_R_MALLOC_FAILURE);
        return 0;
    }
    if (!SSL_set_ex_data(ssl, dane_idx, dane)) {
        DANEerr(DANE_F_SSL_DANE_INIT, ERR_R_MALLOC_FAILURE);
        OPENSSL_free(dane);
        return 0;
    }

    dane->pkeys = 0;
    dane->certs = 0;
    dane->chain = 0;
    dane->roots = 0;
    dane->depth = -1;
    dane->mhost = 0;                    /* Future SSL control interface */
    dane->multi = 0;                    /* Future SSL control interface */
    dane->count = 0;

    for (i = 0; i <= SSL_DANE_USAGE_LAST; ++i)
        dane->selectors[i] = 0;

    if (hostnames && (dane->hosts = host_list_init(hostnames)) == 0) {
        DANEerr(DANE_F_SSL_DANE_INIT, ERR_R_MALLOC_FAILURE);
        DANESSL_cleanup(ssl);
        return 0;
    }

    return 1;
}

int DANESSL_CTX_init(SSL_CTX *ctx)
{
    if (dane_idx >= 0) {
        SSL_CTX_set_cert_verify_callback(ctx, verify_cert, 0);
        return 1;
    }
    DANEerr(DANE_F_SSL_CTX_DANE_INIT, DANE_R_LIBRARY_INIT);
    return -1;
}

static int init_once(
        volatile int *value,
        int (*init)(void),
        void (*postinit)(void)
)
{
    int wlock = 0;

    CRYPTO_r_lock(CRYPTO_LOCK_SSL_CTX);
    if (*value < 0) {
        CRYPTO_r_unlock(CRYPTO_LOCK_SSL_CTX);
        CRYPTO_w_lock(CRYPTO_LOCK_SSL_CTX);
        wlock = 1;
        if (*value < 0) {
            *value = init();
            if (postinit)
                postinit();
        }
    }
    if (wlock)
        CRYPTO_w_unlock(CRYPTO_LOCK_SSL_CTX);
    else
        CRYPTO_r_unlock(CRYPTO_LOCK_SSL_CTX);
    return *value;
}

static void dane_init(void)
{
    /*
     * Store library id in zeroth function slot, used to locate the library
     * name.  This must be done before we load the error strings.
     */
#ifndef OPENSSL_NO_ERR
    dane_str_functs[0].error |= ERR_PACK(err_lib_dane, 0, 0);
    ERR_load_strings(err_lib_dane, dane_str_functs);
    ERR_load_strings(err_lib_dane, dane_str_reasons);
#endif

    /*
     * Register SHA-2 digests, if implemented and not already registered.
     */
#if defined(LN_sha256) && defined(NID_sha256) && !defined(OPENSSL_NO_SHA256)
    if (!EVP_get_digestbyname(LN_sha224))
        EVP_add_digest(EVP_sha224());
    if (!EVP_get_digestbyname(LN_sha256))
        EVP_add_digest(EVP_sha256());
#endif
#if defined(LN_sha512) && defined(NID_sha512) && !defined(OPENSSL_NO_SHA512)
    if (!EVP_get_digestbyname(LN_sha384))
        EVP_add_digest(EVP_sha384());
    if (!EVP_get_digestbyname(LN_sha512))
        EVP_add_digest(EVP_sha512());
#endif

    /*
     * Register an SSL index for the connection-specific SSL_DANE structure.
     * Using a separate index makes it possible to add DANE support to
     * existing OpenSSL releases that don't have a suitable pointer in the
     * SSL structure.
     */
    dane_idx = SSL_get_ex_new_index(0, 0, 0, 0, 0);
}

int DANESSL_library_init(void)
{
    if (err_lib_dane < 0)
        init_once(&err_lib_dane, ERR_get_next_error_library, dane_init);

#if defined(LN_sha256)
    /* No DANE without SHA256 support */
    if (dane_idx >= 0 && EVP_get_digestbyname(LN_sha256) != 0)
        return 1;
#endif
    DANEerr(DANE_F_SSL_DANE_LIBRARY_INIT, DANE_R_DANE_SUPPORT);
    return 0;
}

#endif /* OPENSSL_VERSION_NUMBER */