Tighten parsing of datetime input.

ParseFraction only expects to deal with fields that contain a decimal
point and digit(s).  However it's possible in some edge cases for it
to be passed input that doesn't look like that.  In particular the
input could look like a valid floating-point number, such as ".123e6".
strtod() will happily eat that, possibly producing a result that is
not within the expected range 0..1, which can result in integer
overflow in the callers.  That doesn't have any security consequences,
but it's still not very desirable.  Fix by checking that the input
has the expected form.

Similarly, DecodeNumberField only expects to deal with fields that
contain a decimal point and digit(s), but it's sometimes abused to
parse strings that might not look like that.  This could result in
failure to reject bogus input, yielding silly results.  Again, fix
by rejecting input that doesn't look as-expected.  That decision
also means that we can affirmatively answer the very old comment
questioning whether we couldn't save some duplicative code by
using ParseFractionalSecond here.

While these changes should only reject input that nobody would
consider valid, it still doesn't seem like a change to make in
stable branches.  Apply to HEAD only.

Reported-by: Evgeniy Gorbanev <gorbanev.es@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/1328335.1748371099@sss.pgh.pa.us

src/backend/utils/adt/datetime.c

@@ -702,9 +702,18 @@ ParseFraction(char *cp, double *frac)
 	}
 	else
 	{
+		/*
+		 * On the other hand, let's reject anything that's not digits after
+		 * the ".".  strtod is happy with input like ".123e9", but that'd
+		 * break callers' expectation that the result is in 0..1.  (It's quite
+		 * difficult to get here with such input, but not impossible.)
+		 */
+		if (strspn(cp + 1, "0123456789") != strlen(cp + 1))
+			return DTERR_BAD_FORMAT;
+
 		errno = 0;
 		*frac = strtod(cp, &cp);
-		/* check for parse failure */
+		/* check for parse failure (probably redundant given prior check) */
 		if (*cp != '\0' || errno != 0)
 			return DTERR_BAD_FORMAT;
 	}
@@ -2958,31 +2967,28 @@ DecodeNumberField(int len, char *str, int fmask,
 {
 	char	   *cp;
 
+	/*
+	 * This function was originally meant to cope only with DTK_NUMBER fields,
+	 * but we now sometimes abuse it to parse (parts of) DTK_DATE fields,
+	 * which can contain letters and other punctuation.  Reject if it's not a
+	 * valid DTK_NUMBER, that is digits and decimal point(s).  (ParseFraction
+	 * will reject if there's more than one decimal point.)
+	 */
+	if (strspn(str, "0123456789.") != len)
+		return DTERR_BAD_FORMAT;
+
 	/*
 	 * Have a decimal point? Then this is a date or something with a seconds
 	 * field...
 	 */
 	if ((cp = strchr(str, '.')) != NULL)
 	{
-		/*
-		 * Can we use ParseFractionalSecond here?  Not clear whether trailing
-		 * junk should be rejected ...
-		 */
-		if (cp[1] == '\0')
-		{
-			/* avoid assuming that strtod will accept "." */
-			*fsec = 0;
-		}
-		else
-		{
-			double		frac;
+		int			dterr;
 
-			errno = 0;
-			frac = strtod(cp, NULL);
-			if (errno != 0)
-				return DTERR_BAD_FORMAT;
-			*fsec = rint(frac * 1000000);
-		}
+		/* Convert the fraction and store at *fsec */
+		dterr = ParseFractionalSecond(cp, fsec);
+		if (dterr)
+			return dterr;
 		/* Now truncate off the fraction for further processing */
 		*cp = '\0';
 		len = strlen(str);

src/test/regress/expected/horology.out

@@ -467,6 +467,15 @@ SELECT timestamp with time zone 'Y2001M12D27H04MM05S06.789-08';
 ERROR:  invalid input syntax for type timestamp with time zone: "Y2001M12D27H04MM05S06.789-08"
 LINE 1: SELECT timestamp with time zone 'Y2001M12D27H04MM05S06.789-0...
                                         ^
+-- More examples we used to accept and should not
+SELECT timestamp with time zone 'J2452271 T X03456-08';
+ERROR:  invalid input syntax for type timestamp with time zone: "J2452271 T X03456-08"
+LINE 1: SELECT timestamp with time zone 'J2452271 T X03456-08';
+                                        ^
+SELECT timestamp with time zone 'J2452271 T X03456.001e6-08';
+ERROR:  invalid input syntax for type timestamp with time zone: "J2452271 T X03456.001e6-08"
+LINE 1: SELECT timestamp with time zone 'J2452271 T X03456.001e6-08'...
+                                        ^
 -- conflicting fields should throw errors
 SELECT date '1995-08-06 epoch';
 ERROR:  invalid input syntax for type date: "1995-08-06 epoch"

src/test/regress/sql/horology.sql

@@ -102,6 +102,10 @@ SELECT date 'J J 1520447';
 SELECT timestamp with time zone 'Y2001M12D27H04M05S06.789+08';
 SELECT timestamp with time zone 'Y2001M12D27H04MM05S06.789-08';
 
+-- More examples we used to accept and should not
+SELECT timestamp with time zone 'J2452271 T X03456-08';
+SELECT timestamp with time zone 'J2452271 T X03456.001e6-08';
+
 -- conflicting fields should throw errors
 SELECT date '1995-08-06 epoch';
 SELECT date '1995-08-06 infinity';