X509 time: tighten validation per RFC 5280

- Reject fractional seconds
- Reject offsets
- Check that the date/time digits are in valid range.
- Add documentation for X509_cmp_time

GH issue 2620
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>

CHANGES

@@ -4,6 +4,11 @@
 
  Changes between 1.1.0e and 1.1.1 [xx XXX xxxx]
 
+  *) Certificate time validation (X509_cmp_time) enforces stricter
+     compliance with RFC 5280. Fractional seconds and timezone offsets
+     are no longer allowed.
+     [Emilia Käsper]
+
   *) Add support for SipHash
      [Todd Short]
 

crypto/x509/x509_vfy.c

@@ -7,6 +7,7 @@
  * https://www.openssl.org/source/license.html
  */
 
+#include <ctype.h>
 #include <stdio.h>
 #include <time.h>
 #include <errno.h>
@@ -1754,119 +1755,67 @@ int X509_cmp_current_time(const ASN1_TIME *ctm)
 
 int X509_cmp_time(const ASN1_TIME *ctm, time_t *cmp_time)
 {
-    char *str;
-    ASN1_TIME atm;
-    long offset;
-    char buff1[24], buff2[24], *p;
-    int i, j, remaining;
+    static const size_t utctime_length = sizeof("YYMMDDHHMMSSZ") - 1;
+    static const size_t generalizedtime_length = sizeof("YYYYMMDDHHMMSSZ") - 1;
+    ASN1_TIME *asn1_cmp_time = NULL;
+    int i, day, sec, ret = 0;
 
-    p = buff1;
-    remaining = ctm->length;
-    str = (char *)ctm->data;
     /*
-     * Note that the following (historical) code allows much more slack in the
-     * time format than RFC5280. In RFC5280, the representation is fixed:
+     * Note that ASN.1 allows much more slack in the time format than RFC5280.
+     * In RFC5280, the representation is fixed:
      * UTCTime: YYMMDDHHMMSSZ
      * GeneralizedTime: YYYYMMDDHHMMSSZ
+     *
+     * We do NOT currently enforce the following RFC 5280 requirement:
+     * "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."
      */
-    if (ctm->type == V_ASN1_UTCTIME) {
-        /* YYMMDDHHMM[SS]Z or YYMMDDHHMM[SS](+-)hhmm */
-        int min_length = sizeof("YYMMDDHHMMZ") - 1;
-        int max_length = sizeof("YYMMDDHHMMSS+hhmm") - 1;
-        if (remaining < min_length || remaining > max_length)
+    switch (ctm->type) {
+    case V_ASN1_UTCTIME:
+        if (ctm->length != (int)(utctime_length))
             return 0;
-        memcpy(p, str, 10);
-        p += 10;
-        str += 10;
-        remaining -= 10;
-    } else {
-        /* YYYYMMDDHHMM[SS[.fff]]Z or YYYYMMDDHHMM[SS[.f[f[f]]]](+-)hhmm */
-        int min_length = sizeof("YYYYMMDDHHMMZ") - 1;
-        int max_length = sizeof("YYYYMMDDHHMMSS.fff+hhmm") - 1;
-        if (remaining < min_length || remaining > max_length)
+        break;
+    case V_ASN1_GENERALIZEDTIME:
+        if (ctm->length != (int)(generalizedtime_length))
             return 0;
-        memcpy(p, str, 12);
-        p += 12;
-        str += 12;
-        remaining -= 12;
-    }
-
-    if ((*str == 'Z') || (*str == '-') || (*str == '+')) {
-        *(p++) = '0';
-        *(p++) = '0';
-    } else {
-        /* SS (seconds) */
-        if (remaining < 2)
-            return 0;
-        *(p++) = *(str++);
-        *(p++) = *(str++);
-        remaining -= 2;
-        /*
-         * Skip any (up to three) fractional seconds...
-         * TODO(emilia): in RFC5280, fractional seconds are forbidden.
-         * Can we just kill them altogether?
-         */
-        if (remaining && *str == '.') {
-            str++;
-            remaining--;
-            for (i = 0; i < 3 && remaining; i++, str++, remaining--) {
-                if (*str < '0' || *str > '9')
         break;
+    default:
+        return 0;
     }
-        }
-
-    }
-    *(p++) = 'Z';
-    *(p++) = '\0';
 
-    /* We now need either a terminating 'Z' or an offset. */
-    if (!remaining)
-        return 0;
-    if (*str == 'Z') {
-        if (remaining != 1)
-            return 0;
-        offset = 0;
-    } else {
-        /* (+-)HHMM */
-        if ((*str != '+') && (*str != '-'))
-            return 0;
-        /* Historical behaviour: the (+-)hhmm offset is forbidden in RFC5280. */
-        if (remaining != 5)
-            return 0;
-        if (str[1] < '0' || str[1] > '9' || str[2] < '0' || str[2] > '9' ||
-            str[3] < '0' || str[3] > '9' || str[4] < '0' || str[4] > '9')
+    /**
+     * Verify the format: the ASN.1 functions we use below allow a more
+     * flexible format than what's mandated by RFC 5280.
+     * Digit and date ranges will be verified in the conversion methods.
+     */
+    for (i = 0; i < ctm->length - 1; i++) {
+        if (!isdigit(ctm->data[i]))
             return 0;
-        offset = ((str[1] - '0') * 10 + (str[2] - '0')) * 60;
-        offset += (str[3] - '0') * 10 + (str[4] - '0');
-        if (*str == '-')
-            offset = -offset;
     }
-    atm.type = ctm->type;
-    atm.flags = 0;
-    atm.length = sizeof(buff2);
-    atm.data = (unsigned char *)buff2;
-
-    if (X509_time_adj(&atm, offset * 60, cmp_time) == NULL)
+    if (ctm->data[ctm->length - 1] != 'Z')
         return 0;
 
-    if (ctm->type == V_ASN1_UTCTIME) {
-        i = (buff1[0] - '0') * 10 + (buff1[1] - '0');
-        if (i < 50)
-            i += 100;           /* cf. RFC 2459 */
-        j = (buff2[0] - '0') * 10 + (buff2[1] - '0');
-        if (j < 50)
-            j += 100;
+    /*
+     * There is ASN1_UTCTIME_cmp_time_t but no
+     * ASN1_GENERALIZEDTIME_cmp_time_t or ASN1_TIME_cmp_time_t,
+     * so we go through ASN.1
+     */
+    asn1_cmp_time = X509_time_adj(NULL, 0, cmp_time);
+    if (asn1_cmp_time == NULL)
+        goto err;
+    if (!ASN1_TIME_diff(&day, &sec, ctm, asn1_cmp_time))
+        goto err;
 
-        if (i < j)
-            return -1;
-        if (i > j)
-            return 1;
-    }
-    i = strcmp(buff1, buff2);
-    if (i == 0)                 /* wait a second then return younger :-) */
-        return -1;
-    else
-        return i;
+    /*
+     * X509_cmp_time comparison is <=.
+     * The return value 0 is reserved for errors.
+     */
+    ret = (day >= 0 && sec >= 0) ? -1 : 1;
+
+ err:
+    ASN1_TIME_free(asn1_cmp_time);
+    return ret;
 }
 
 ASN1_TIME *X509_gmtime_adj(ASN1_TIME *s, long adj)

doc/man3/X509_cmp_time.pod

+=pod
+
+=head1 NAME
+
+X509_cmp_time - X509 time functions
+
+=head1 SYNOPSIS
+
+ X509_cmp_time(const ASN1_TIME *asn1_time, time_t *cmp_time);
+
+=head1 DESCRIPTION
+
+X509_cmp_time() compares the ASN1_TIME in B<asn1_time> with the time in
+<cmp_time>.
+
+B<asn1_time> must satisfy the ASN1_TIME format mandated by RFC 5280, i.e.,
+its format must be either YYMMDDHHMMSSZ or YYYYMMDDHHMMSSZ.
+
+If B<cmp_time> is NULL the current time is used.
+
+=head1 BUGS
+
+Unlike many standard comparison functions, X509_cmp_time returns 0 on error.
+
+=head1 RETURN VALUES
+
+X509_cmp_time() returns -1 if B<asn1_time> is earlier than, or equal to,
+B<cmp_time>, and 1 otherwise. It returns 0 on error.
+
+=head1 COPYRIGHT
+
+Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the OpenSSL license (the "License").  You may not use
+this file except in compliance with the License.  You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut

test/build.info

@@ -28,7 +28,7 @@ IF[{- !$disabled{tests} -}]
           dtlsv1listentest ct_test threadstest afalgtest d2i_test \
           ssl_test_ctx_test ssl_test x509aux cipherlist_test asynciotest \
           bioprinttest sslapitest dtlstest sslcorrupttest bio_enc_test \
-          pkey_meth_test uitest cipherbytes_test
+          pkey_meth_test uitest cipherbytes_test x509_time_test
 
   SOURCE[aborttest]=aborttest.c
   INCLUDE[aborttest]=../include
@@ -295,6 +295,10 @@ IF[{- !$disabled{tests} -}]
   INCLUDE[pkey_meth_test]=../include
   DEPEND[pkey_meth_test]=../libcrypto
 
+  SOURCE[x509_time_test]=x509_time_test.c testutil.c test_main.c
+  INCLUDE[x509_time_test]=.. ../include
+  DEPEND[x509_time_test]=../libcrypto
+
   IF[{- !$disabled{psk} -}]
     PROGRAMS_NO_INST=dtls_mtu_test
     SOURCE[dtls_mtu_test]=dtls_mtu_test.c ssltestlib.c

test/recipes/60-test_x509_time.t

+#! /usr/bin/env perl
+# Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
+#
+# Licensed under the OpenSSL license (the "License").  You may not use
+# this file except in compliance with the License.  You can obtain a copy
+# in the file LICENSE in the source distribution or at
+# https://www.openssl.org/source/license.html
+
+
+use OpenSSL::Test::Simple;
+
+simple_test("test_x509_time", "x509_time_test");

test/x509_time_test.c

+/*
+ * Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the OpenSSL license (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+/* Tests for X509 time functions */
+
+#include <string.h>
+#include <time.h>
+
+#include <openssl/asn1.h>
+#include <openssl/x509.h>
+#include "testutil.h"
+#include "test_main.h"
+#include "e_os.h"
+
+typedef struct {
+    const char *data;
+    int type;
+    time_t cmp_time;
+    /* -1 if asn1_time <= cmp_time, 1 if asn1_time > cmp_time, 0 if error. */
+    int expected;
+} TESTDATA;
+
+static TESTDATA x509_cmp_tests[] = {
+    {
+        "20170217180154Z", V_ASN1_GENERALIZEDTIME,
+        /* The same in seconds since epoch. */
+        1487354514, -1,
+    },
+    {
+        "20170217180154Z", V_ASN1_GENERALIZEDTIME,
+        /* One second more. */
+        1487354515, -1,
+    },
+    {
+        "20170217180154Z", V_ASN1_GENERALIZEDTIME,
+        /* One second less. */
+        1487354513, 1,
+    },
+    /* Same as UTC time. */
+    {
+        "170217180154Z", V_ASN1_UTCTIME,
+        /* The same in seconds since epoch. */
+        1487354514, -1,
+    },
+    {
+        "170217180154Z", V_ASN1_UTCTIME,
+        /* One second more. */
+        1487354515, -1,
+    },
+    {
+        "170217180154Z", V_ASN1_UTCTIME,
+        /* One second less. */
+        1487354513, 1,
+    },
+    /* UTCTime from the 20th century. */
+    {
+        "990217180154Z", V_ASN1_UTCTIME,
+        /* The same in seconds since epoch. */
+        919274514, -1,
+    },
+    {
+        "990217180154Z", V_ASN1_UTCTIME,
+        /* One second more. */
+        919274515, -1,
+    },
+    {
+        "990217180154Z", V_ASN1_UTCTIME,
+        /* One second less. */
+        919274513, 1,
+    },
+    /* Various invalid formats. */
+    {
+        /* No trailing Z. */
+        "20170217180154", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* No trailing Z, UTCTime. */
+        "170217180154", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+        /* No seconds. */
+        "201702171801Z", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* No seconds, UTCTime. */
+        "1702171801Z", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+        /* Fractional seconds. */
+        "20170217180154.001Z", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* Fractional seconds, UTCTime. */
+        "170217180154.001Z", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+        /* Timezone offset. */
+        "20170217180154+0100", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* Timezone offset, UTCTime. */
+        "170217180154+0100", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+        /* Extra digits. */
+        "2017021718015400Z", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* Extra digits, UTCTime. */
+        "17021718015400Z", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+        /* Non-digits. */
+        "2017021718015aZ", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* Non-digits, UTCTime. */
+        "17021718015aZ", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+        /* Trailing garbage. */
+        "20170217180154Zlongtrailinggarbage", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* Trailing garbage, UTCTime. */
+        "170217180154Zlongtrailinggarbage", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+         /* Swapped type. */
+        "20170217180154Z", V_ASN1_UTCTIME, 0, 0,
+    },
+    {
+        /* Swapped type. */
+        "170217180154Z", V_ASN1_GENERALIZEDTIME, 0, 0,
+    },
+    {
+        /* Bad type. */
+        "20170217180154Z", V_ASN1_OCTET_STRING, 0, 0,
+    },
+};
+
+static int test_x509_cmp_time(int idx)
+{
+    ASN1_TIME t;
+    int result;
+
+    memset(&t, 0, sizeof(t));
+    t.type = x509_cmp_tests[idx].type;
+    t.data = (unsigned char*)(x509_cmp_tests[idx].data);
+    t.length = strlen(x509_cmp_tests[idx].data);
+
+    result = X509_cmp_time(&t, &x509_cmp_tests[idx].cmp_time);
+    if (result != x509_cmp_tests[idx].expected) {
+        fprintf(stderr, "test_x509_cmp_time(%d) failed: expected %d, got %d\n",
+                idx, x509_cmp_tests[idx].expected, result);
+        return 0;
+    }
+    return 1;
+}
+
+static int test_x509_cmp_time_current()
+{
+    time_t now = time(NULL);
+    /* Pick a day earlier and later, relative to any system clock. */
+    ASN1_TIME *asn1_before = NULL, *asn1_after = NULL;
+    int cmp_result, failed = 0;
+
+    asn1_before = ASN1_TIME_adj(NULL, now, -1, 0);
+    asn1_after = ASN1_TIME_adj(NULL, now, 1, 0);
+
+    cmp_result  = X509_cmp_time(asn1_before, NULL);
+    if (cmp_result != -1) {
+        fprintf(stderr, "test_x509_cmp_time_current failed: expected -1, got %d\n",
+                cmp_result);
+        failed = 1;
+    }
+
+    cmp_result = X509_cmp_time(asn1_after, NULL);
+    if (cmp_result != 1) {
+        fprintf(stderr, "test_x509_cmp_time_current failed: expected 1, got %d\n",
+                cmp_result);
+        failed = 1;
+    }
+
+    ASN1_TIME_free(asn1_before);
+    ASN1_TIME_free(asn1_after);
+
+    return failed == 0;
+}
+
+void register_tests()
+{
+    ADD_TEST(test_x509_cmp_time_current);
+    ADD_ALL_TESTS(test_x509_cmp_time, OSSL_NELEM(x509_cmp_tests));
+}