path: root/libfetch/openssl-compat.c

#include <string.h>
#include <strings.h>
#include "openssl-compat.h"

#ifdef OSSL_COMPAT_NEED_X509_CHECK

/* libressl 2.5.5 implementation of X509_check_host() */

typedef int (*equal_fn) (const unsigned char *pattern, size_t pattern_len,
    const unsigned char *subject, size_t subject_len, unsigned int flags);

/* Skip pattern prefix to match "wildcard" subject */
static void skip_prefix(const unsigned char **p, size_t *plen,
    const unsigned char *subject, size_t subject_len, unsigned int flags)
{
	const unsigned char *pattern = *p;
	size_t pattern_len = *plen;

	/*
	 * If subject starts with a leading '.' followed by more octets, and
	 * pattern is longer, compare just an equal-length suffix with the
	 * full subject (starting at the '.'), provided the prefix contains
	 * no NULs.
	 */
	if ((flags & _X509_CHECK_FLAG_DOT_SUBDOMAINS) == 0)
		return;

	while (pattern_len > subject_len && *pattern) {
		if ((flags & X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS) &&
		    *pattern == '.')
			break;
		++pattern;
		--pattern_len;
	}

	/* Skip if entire prefix acceptable */
	if (pattern_len == subject_len) {
		*p = pattern;
		*plen = pattern_len;
	}
}

/*
 * Open/BoringSSL uses memcmp for "equal_case" while their
 * "equal_nocase" function is a hand-rolled strncasecmp that does not
 * allow \0 in the pattern. Since an embedded \0 is likely a sign of
 * problems, we simply don't allow it in either case, and then we use
 * standard libc funcitons.
 */

/* Compare using strncasecmp */
static int equal_nocase(const unsigned char *pattern, size_t pattern_len,
    const unsigned char *subject, size_t subject_len,
    unsigned int flags)
{
	if (memchr(pattern, '\0', pattern_len) != NULL)
		return 0;
	if (memchr(subject, '\0', subject_len) != NULL)
		return 0;
	skip_prefix(&pattern, &pattern_len, subject, subject_len, flags);
	if (pattern_len != subject_len)
		return 0;
	return (strncasecmp((const char *)pattern, (const char *)subject, pattern_len) == 0);
}

/* Compare using strncmp. */
static int equal_case(const unsigned char *pattern, size_t pattern_len,
    const unsigned char *subject, size_t subject_len,
    unsigned int flags)
{
	if (memchr(pattern, 0, pattern_len) != NULL)
		return 0;
	if (memchr(subject, 0, subject_len) != NULL)
		return 0;
	skip_prefix(&pattern, &pattern_len, subject, subject_len, flags);
	if (pattern_len != subject_len)
		return 0;
	return (strncmp((const char *)pattern, (const char *)subject, pattern_len) == 0);
}

/*
 * RFC 5280, section 7.5, requires that only the domain is compared in a
 * case-insensitive manner.
 */
static int equal_email(const unsigned char *a, size_t a_len,
    const unsigned char *b, size_t b_len,
    unsigned int unused_flags)
{
	size_t pos = a_len;
	if (a_len != b_len)
		return 0;
	/*
	 * We search backwards for the '@' character, so that we do not have to
	 * deal with quoted local-parts.  The domain part is compared in a
	 * case-insensitive manner.
	 */
	while (pos > 0) {
		pos--;
		if (a[pos] == '@' || b[pos] == '@') {
			if (!equal_nocase(a + pos, a_len - pos, b + pos, a_len - pos, 0))
				return 0;
			break;
		}
	}
	if (pos == 0)
		pos = a_len;
	return equal_case(a, pos, b, pos, 0);
}

/*
 * Compare the prefix and suffix with the subject, and check that the
 * characters in-between are valid.
 */
static int wildcard_match(const unsigned char *prefix, size_t prefix_len,
    const unsigned char *suffix, size_t suffix_len,
    const unsigned char *subject, size_t subject_len, unsigned int flags)
{
	const unsigned char *wildcard_start;
	const unsigned char *wildcard_end;
	const unsigned char *p;
	int allow_multi = 0;
	int allow_idna = 0;

	if (subject_len < prefix_len + suffix_len)
		return 0;
	if (!equal_nocase(prefix, prefix_len, subject, prefix_len, flags))
		return 0;
	wildcard_start = subject + prefix_len;
	wildcard_end = subject + (subject_len - suffix_len);
	if (!equal_nocase(wildcard_end, suffix_len, suffix, suffix_len, flags))
		return 0;
	/*
	 * If the wildcard makes up the entire first label, it must match at
	 * least one character.
	 */
	if (prefix_len == 0 && *suffix == '.') {
		if (wildcard_start == wildcard_end)
			return 0;
		allow_idna = 1;
		if (flags & X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS)
			allow_multi = 1;
	}
	/* IDNA labels cannot match partial wildcards */
	if (!allow_idna &&
	    subject_len >= 4
	    && strncasecmp((const char *)subject, "xn--", 4) == 0)
		return 0;
	/* The wildcard may match a literal '*' */
	if (wildcard_end == wildcard_start + 1 && *wildcard_start == '*')
		return 1;
	/*
	 * Check that the part matched by the wildcard contains only
	 * permitted characters and only matches a single label unless
	 * allow_multi is set.
	 */
	for (p = wildcard_start; p != wildcard_end; ++p)
		if (!(('0' <= *p && *p <= '9') || ('A' <= *p && *p <= 'Z') ||
		    ('a' <= *p && *p <= 'z') || *p == '-' ||
		    (allow_multi && *p == '.')))
			return 0;
	return 1;
}

#define LABEL_START     (1 << 0)
#define LABEL_END       (1 << 1)
#define LABEL_HYPHEN    (1 << 2)
#define LABEL_IDNA      (1 << 3)

static const unsigned char *valid_star(const unsigned char *p, size_t len,
    unsigned int flags)
{
	const unsigned char *star = 0;
	size_t i;
	int state = LABEL_START;
	int dots = 0;
	for (i = 0; i < len; ++i) {
		/*
		 * Locate first and only legal wildcard, either at the start
		 * or end of a non-IDNA first and not final label.
		 */
		if (p[i] == '*') {
			int atstart = (state & LABEL_START);
			int atend = (i == len - 1 || p[i + 1] == '.');
			/*
			 * At most one wildcard per pattern.
			 * No wildcards in IDNA labels.
			 * No wildcards after the first label.
			 */
			if (star != NULL || (state & LABEL_IDNA) != 0 || dots)
				return NULL;
			/* Only full-label '*.example.com' wildcards? */
			if ((flags & X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS)
			    && (!atstart || !atend))
				return NULL;
			/* No 'foo*bar' wildcards */
			if (!atstart && !atend)
				return NULL;
			star = &p[i];
			state &= ~LABEL_START;
		} else if ((state & LABEL_START) != 0) {
			/*
			 * At the start of a label, skip any "xn--" and
			 * remain in the LABEL_START state, but set the
			 * IDNA label state
			 */
			if ((state & LABEL_IDNA) == 0 && len - i >= 4
			    && strncasecmp((const char *)&p[i], "xn--", 4) == 0) {
				i += 3;
				state |= LABEL_IDNA;
				continue;
			}
			/* Labels must start with a letter or digit */
			state &= ~LABEL_START;
			if (('a' <= p[i] && p[i] <= 'z')
			    || ('A' <= p[i] && p[i] <= 'Z')
			    || ('0' <= p[i] && p[i] <= '9'))
				continue;
			return NULL;
		} else if (('a' <= p[i] && p[i] <= 'z')
		    || ('A' <= p[i] && p[i] <= 'Z')
		    || ('0' <= p[i] && p[i] <= '9')) {
			state &= LABEL_IDNA;
			continue;
		} else if (p[i] == '.') {
			if (state & (LABEL_HYPHEN | LABEL_START))
				return NULL;
			state = LABEL_START;
			++dots;
		} else if (p[i] == '-') {
			/* no domain/subdomain starts with '-' */
			if ((state & LABEL_START) != 0)
				return NULL;
			state |= LABEL_HYPHEN;
		} else
			return NULL;
	}

	/*
	 * The final label must not end in a hyphen or ".", and
	 * there must be at least two dots after the star.
	 */
	if ((state & (LABEL_START | LABEL_HYPHEN)) != 0 || dots < 2)
		return NULL;
	return star;
}

/* Compare using wildcards. */
static int equal_wildcard(const unsigned char *pattern, size_t pattern_len,
    const unsigned char *subject, size_t subject_len, unsigned int flags)
{
	const unsigned char *star = NULL;

	/*
	 * Subject names starting with '.' can only match a wildcard pattern
	 * via a subject sub-domain pattern suffix match.
	 */
	if (!(subject_len > 1 && subject[0] == '.'))
		star = valid_star(pattern, pattern_len, flags);
	if (star == NULL)
		return equal_nocase(pattern, pattern_len,
		    subject, subject_len, flags);
	return wildcard_match(pattern, star - pattern,
	    star + 1, (pattern + pattern_len) - star - 1,
	    subject, subject_len, flags);
}

/*
 * Compare an ASN1_STRING to a supplied string. If they match return 1. If
 * cmp_type > 0 only compare if string matches the type, otherwise convert it
 * to UTF8.
 */

static int
do_check_string(ASN1_STRING *a, int cmp_type, equal_fn equal,
    unsigned int flags, const char *b, size_t blen, char **peername)
{
	int rv = 0;

	if (!a->data || !a->length)
		return 0;
	if (cmp_type > 0) {
		if (cmp_type != a->type)
			return 0;
		if (cmp_type == V_ASN1_IA5STRING)
			rv = equal(a->data, a->length, (unsigned char *)b,
			    blen, flags);
		else if (a->length == (int)blen && !memcmp(a->data, b, blen))
			rv = 1;
		if (rv > 0 && peername &&
		    (*peername = strndup((char *)a->data, a->length)) == NULL)
			rv = -1;
	} else {
		int astrlen;
		unsigned char *astr;
		astrlen = ASN1_STRING_to_UTF8(&astr, a);
		if (astrlen < 0)
			return -1;
		rv = equal(astr, astrlen, (unsigned char *)b, blen, flags);
		if (rv > 0 && peername &&
		    (*peername = strndup((char *)astr, astrlen)) == NULL)
			rv = -1;
		free(astr);
	}
	return rv;
}

static int do_x509_check(X509 *x, const char *chk, size_t chklen,
    unsigned int flags, int check_type, char **peername)
{
	GENERAL_NAMES *gens = NULL;
	X509_NAME *name = NULL;
	size_t i;
	int j;
	int cnid = NID_undef;
	int alt_type;
	int san_present = 0;
	int rv = 0;
	equal_fn equal;

	/* See below, this flag is internal-only */
	flags &= ~_X509_CHECK_FLAG_DOT_SUBDOMAINS;
	if (check_type == GEN_EMAIL) {
		cnid = NID_pkcs9_emailAddress;
		alt_type = V_ASN1_IA5STRING;
		equal = equal_email;
	} else if (check_type == GEN_DNS) {
		cnid = NID_commonName;
		/* Implicit client-side DNS sub-domain pattern */
		if (chklen > 1 && chk[0] == '.')
			flags |= _X509_CHECK_FLAG_DOT_SUBDOMAINS;
		alt_type = V_ASN1_IA5STRING;
		if (flags & X509_CHECK_FLAG_NO_WILDCARDS)
			equal = equal_nocase;
		else
			equal = equal_wildcard;
	} else {
		alt_type = V_ASN1_OCTET_STRING;
		equal = equal_case;
	}

	gens = X509_get_ext_d2i(x, NID_subject_alt_name, NULL, NULL);
	if (gens != NULL) {
		for (i = 0; i < sk_GENERAL_NAME_num(gens); i++) {
			GENERAL_NAME *gen;
			ASN1_STRING *cstr;
			gen = sk_GENERAL_NAME_value(gens, i);
			if (gen->type != check_type)
				continue;
			san_present = 1;
			if (check_type == GEN_EMAIL)
				cstr = gen->d.rfc822Name;
			else if (check_type == GEN_DNS)
				cstr = gen->d.dNSName;
			else
				cstr = gen->d.iPAddress;
			/* Positive on success, negative on error! */
			if ((rv = do_check_string(cstr, alt_type, equal, flags,
			    chk, chklen, peername)) != 0)
				break;
		}
		GENERAL_NAMES_free(gens);
		if (rv != 0)
			return rv;
		if (cnid == NID_undef ||
		    (san_present &&
		    !(flags & X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT)))
			return 0;
	}

	/* We're done if CN-ID is not pertinent */
	if (cnid == NID_undef)
		return 0;

	j = -1;
	name = X509_get_subject_name(x);
	while ((j = X509_NAME_get_index_by_NID(name, cnid, j)) >= 0) {
		X509_NAME_ENTRY *ne;
		ASN1_STRING *str;
		if ((ne = X509_NAME_get_entry(name, j)) == NULL)
			return -1;
		if ((str = X509_NAME_ENTRY_get_data(ne)) == NULL)
			return -1;
		/* Positive on success, negative on error! */
		if ((rv = do_check_string(str, -1, equal, flags,
			 chk, chklen, peername)) != 0)
			return rv;
	}
	return 0;
}

int X509_check_host(X509 *x, const char *chk, size_t chklen,
    unsigned int flags, char **peername)
{
	if (chk == NULL)
		return -2;
	if (memchr(chk, '\0', chklen))
		return -2;
	return do_x509_check(x, chk, chklen, flags, GEN_DNS, peername);
}

#endif