asn1: Support dates before 1970-01-01 (i.e. when time_t gets negative)

On x86 we allow "overflows" around 1969/1970 but not for other dates.

Fixes #509.

src/libstrongswan/asn1/asn1.c

@@ -393,8 +393,8 @@ time_t asn1_to_time(const chunk_t *utctime, asn1_t type)
 		tm_year += (tm_year < 50) ? 2000 : 1900;
 	}
 
-	/* prevent large 32 bit integer overflows */
-	if (sizeof(time_t) == 4 && tm_year > 2038)
+	/* prevent obvious 32 bit integer overflows */
+	if (sizeof(time_t) == 4 && (tm_year > 2038 || tm_year < 1901))
 	{
 		return TIME_32_BIT_SIGNED_MAX;
 	}
@@ -435,8 +435,20 @@ time_t asn1_to_time(const chunk_t *utctime, asn1_t type)
 	tm_days = 365 * (tm_year - 1970) + days[tm_mon] + tm_day + tm_leap;
 	tm_secs = 60 * (60 * (24 * tm_days + tm_hour) + tm_min) + tm_sec - tz_offset;
 
-	/* has a 32 bit signed integer overflow occurred? */
-	return (tm_secs < 0) ? TIME_32_BIT_SIGNED_MAX : tm_secs;
+	if (sizeof(time_t) == 4)
+	{	/* has a 32 bit signed integer overflow occurred? */
+		if (tm_year > 1970 && tm_secs < 0)
+		{	/* depending on the time zone, the first days in 1970 may result in
+			 * a negative value, but dates after 1970 never will */
+			return TIME_32_BIT_SIGNED_MAX;
+		}
+		if (tm_year < 1969 && tm_secs > 0)
+		{	/* similarly, tm_secs is not positive for dates before 1970, except
+			 * for the last days in 1969, depending on the time zone */
+			return TIME_32_BIT_SIGNED_MAX;
+		}
+	}
+	return tm_secs;
 }
 
 /**

src/libstrongswan/asn1/asn1.h

@@ -191,6 +191,13 @@ void asn1_debug_simple_object(chunk_t object, asn1_t type, bool private);
 /**
  * Converts an ASN.1 UTCTIME or GENERALIZEDTIME string to time_t
  *
+ * On systems where sizeof(time_t) == 4 there will be an overflow
+ * for dates
+ *   > Tue, 19 Jan 2038 03:14:07 UTC (0x7fffffff)
+ * and
+ *   < Fri, 13 Dec 1901 20:45:52 UTC (0x80000000)
+ * in both cases TIME_32_BIT_SIGNED_MAX is returned.
+ *
  * @param utctime	body of an ASN.1 coded time object
  * @param type		ASN1_UTCTIME or ASN1_GENERALIZEDTIME
  * @return			time_t in UTC

src/libstrongswan/tests/suites/test_asn1.c

@@ -490,6 +490,12 @@ START_TEST(test_asn1_to_time)
 		{            0, 0x17, "7001010260Z" },
 		{            0, 0x17, "7001010203-1Z" },
 		{            0, 0x17, "700101020361Z" },
+		{   -631152000, 0x17, "500101000000Z" }, /* UTCTime min */
+		{           59, 0x17, "691231235959-0001" },
+		{           -1, 0x17, "691231235959Z" },
+		{            0, 0x17, "700101000000Z" },
+		{          -60, 0x17, "700101000000+0001" },
+		{ 2524607999UL, 0x17, "491231235959Z" }, /* UTCTime max */
 		{      5097600, 0x17, "7003010000Z" },
 		{     68256000, 0x17, "7203010000Z" },
 		{    951868800, 0x17, "0003010000Z" },