libfetch: improve openssl/libressl compatibility

X509_check_host() is introduced in libressl-2.5.0 and openssl-1.0.2
which are not yet universally available. Add support for building
against the older versions.

4 files changed, 436 insertions, 7 deletions

diff --git a/libfetch/Makefile b/libfetch/Makefile
index 618348d..12fead9 100644
--- a/libfetch/Makefile
+++ b/libfetch/Makefile
@@ -1,5 +1,5 @@
 libs-y			+= libfetch.a
-libfetch.a-objs		:= common.o fetch.o file.o ftp.o http.o
+libfetch.a-objs		:= common.o fetch.o file.o ftp.o http.o openssl-compat.o
 generate-y		+= ftperr.h httperr.h
 CFLAGS_common.o		+= -DCA_CERT_FILE=\"$(CONFDIR)/ca.pem\" -DCA_CRL_FILE=\"$(CONFDIR)/crl.pem\"
 CFLAGS_common.o		+= -DCLIENT_CERT_FILE=\"$(CONFDIR)/cert.pem\" -DCLIENT_KEY_FILE=\"$(CONFDIR)/cert.key\"
diff --git a/libfetch/common.h b/libfetch/common.h
index b643a34..d7ad1d6 100644
--- a/libfetch/common.h
+++ b/libfetch/common.h
@@ -37,12 +37,7 @@
 #define FTP_DEFAULT_PROXY_PORT	21
 #define HTTP_DEFAULT_PROXY_PORT	3128
 
-#include <openssl/crypto.h>
-#include <openssl/x509.h>
-#include <openssl/x509v3.h>
-#include <openssl/pem.h>
-#include <openssl/ssl.h>
-#include <openssl/err.h>
+#include "openssl-compat.h"
 
 #if defined(__GNUC__) && __GNUC__ >= 3
 #define LIBFETCH_PRINTFLIKE(fmtarg, firstvararg)	\
diff --git a/libfetch/openssl-compat.c b/libfetch/openssl-compat.c
new file mode 100644
index 0000000..3228d17
--- /dev/null
+++ b/libfetch/openssl-compat.c
@@ -0,0 +1,401 @@
+#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
diff --git a/libfetch/openssl-compat.h b/libfetch/openssl-compat.h
new file mode 100644
index 0000000..6b72fda
--- /dev/null
+++ b/libfetch/openssl-compat.h
@@ -0,0 +1,33 @@
+#include <openssl/crypto.h>
+#include <openssl/x509.h>
+#include <openssl/x509v3.h>
+#include <openssl/pem.h>
+#include <openssl/ssl.h>
+#include <openssl/err.h>
+
+#ifndef X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
+#define OSSL_COMPAT_NEED_X509_CHECK 1
+
+/* Flags for X509_check_* functions */
+/* Always check subject name for host match even if subject alt names present */
+#define X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT   0x1
+/* Disable wildcard matching for dnsName fields and common name. */
+#define X509_CHECK_FLAG_NO_WILDCARDS   0x2
+/* Wildcards must not match a partial label. */
+#define X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS 0x4
+/* Allow (non-partial) wildcards to match multiple labels. */
+#define X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS 0x8
+/* Constraint verifier subdomain patterns to match a single labels. */
+#define X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS 0x10
+
+/*
+ * Match reference identifiers starting with "." to any sub-domain.
+ * This is a non-public flag, turned on implicitly when the subject
+ * reference identity is a DNS name.
+ */
+#define _X509_CHECK_FLAG_DOT_SUBDOMAINS 0x8000
+
+int X509_check_host(X509 *x, const char *chk, size_t chklen,
+    unsigned int flags, char **peername);
+
+#endif