Fix possible read past end of string in to_timestamp().

to_timestamp() handles the TH/th format codes by advancing over two input
characters, whatever those are.  It failed to notice whether there were
two characters available to be skipped, making it possible to advance
the pointer past the end of the input string and keep on parsing.
A similar risk existed in the handling of "Y,YYY" format: it would advance
over three characters after the "," whether or not three characters were
available.

In principle this might be exploitable to disclose contents of server
memory.  But the security team concluded that it would be very hard to use
that way, because the parsing loop would stop upon hitting any zero byte,
and TH/th format codes can't be consecutive --- they have to follow some
other format code, which would have to match whatever data is there.
So it seems impractical to examine memory very much beyond the end of the
input string via this bug; and the input string will always be in local
memory not in disk buffers, making it unlikely that anything very
interesting is close to it in a predictable way.  So this doesn't quite
rise to the level of needing a CVE.

Thanks to Wolf Roediger for reporting this bug.

src/backend/utils/adt/formatting.c

@@ -964,7 +964,6 @@ static const char *get_th(char *num, int type);
 static char *str_numth(char *dest, char *num, int type);
 static int	adjust_partial_year_to_2020(int year);
 static int	strspace_len(char *str);
-static int	strdigits_len(char *str);
 static void from_char_set_mode(TmFromChar *tmfc, const FromCharDateMode mode);
 static void from_char_set_int(int *dest, const int value, const FormatNode *node);
 static int	from_char_parse_int_len(int *dest, char **src, const int len, FormatNode *node);
@@ -1976,9 +1975,19 @@ asc_toupper_z(const char *buff)
 
 /* ----------
  * Skip TM / th in FROM_CHAR
+ *
+ * If S_THth is on, skip two chars, assuming there are two available
  * ----------
  */
-#define SKIP_THth(_suf)		(S_THth(_suf) ? 2 : 0)
+#define SKIP_THth(ptr, _suf) \
+	do { \
+		if (S_THth(_suf)) \
+		{ \
+			if (*(ptr)) (ptr)++; \
+			if (*(ptr)) (ptr)++; \
+		} \
+	} while (0)
+
 
 #ifdef DEBUG_TO_FROM_CHAR
 /* -----------
@@ -2086,23 +2095,6 @@ strspace_len(char *str)
 	return len;
 }
 
-static int
-strdigits_len(char *str)
-{
-	char	   *p = str;
-	int			len;
-
-	len = strspace_len(str);
-	p += len;
-
-	while (*p && isdigit((unsigned char) *p) && len <= DCH_MAX_ITEM_SIZ)
-	{
-		len++;
-		p++;
-	}
-	return len;
-}
-
 /*
  * Set the date mode of a from-char conversion.
  *
@@ -3007,19 +2999,19 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 			case DCH_HH12:
 				from_char_parse_int_len(&out->hh, &s, 2, n);
 				out->clock = CLOCK_12_HOUR;
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_HH24:
 				from_char_parse_int_len(&out->hh, &s, 2, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_MI:
 				from_char_parse_int(&out->mi, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_SS:
 				from_char_parse_int(&out->ss, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_MS:		/* millisecond */
 				len = from_char_parse_int_len(&out->ms, &s, 3, n);
@@ -3030,7 +3022,7 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 				out->ms *= len == 1 ? 100 :
 					len == 2 ? 10 : 1;
 
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_US:		/* microsecond */
 				len = from_char_parse_int_len(&out->us, &s, 6, n);
@@ -3041,11 +3033,11 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 					len == 4 ? 100 :
 					len == 5 ? 10 : 1;
 
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_SSSS:
 				from_char_parse_int(&out->ssss, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_tz:
 			case DCH_TZ:
@@ -3085,7 +3077,7 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 				break;
 			case DCH_MM:
 				from_char_parse_int(&out->mm, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_DAY:
 			case DCH_Day:
@@ -3105,31 +3097,31 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 				break;
 			case DCH_DDD:
 				from_char_parse_int(&out->ddd, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_IDDD:
 				from_char_parse_int_len(&out->ddd, &s, 3, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_DD:
 				from_char_parse_int(&out->dd, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_D:
 				from_char_parse_int(&out->d, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_ID:
 				from_char_parse_int_len(&out->d, &s, 1, n);
 				/* Shift numbering to match Gregorian where Sunday = 1 */
 				if (++out->d > 7)
 					out->d = 1;
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_WW:
 			case DCH_IW:
 				from_char_parse_int(&out->ww, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_Q:
 
@@ -3144,55 +3136,57 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 				 * isn't stored anywhere in 'out'.
 				 */
 				from_char_parse_int((int *) NULL, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_CC:
 				from_char_parse_int(&out->cc, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_Y_YYY:
 				{
 					int			matched,
 								years,
-								millenia;
+								millenia,
+								nch;
 
-					matched = sscanf(s, "%d,%03d", &millenia, &years);
+					matched = sscanf(s, "%d,%03d%n", &millenia, &years, &nch);
-					if (matched != 2)
+					if (matched < 2)
 						ereport(ERROR,
 								(errcode(ERRCODE_INVALID_DATETIME_FORMAT),
 							  errmsg("invalid input string for \"Y,YYY\"")));
 					years += (millenia * 1000);
 					from_char_set_int(&out->year, years, n);
 					out->yysz = 4;
-					s += strdigits_len(s) + 4 + SKIP_THth(n->suffix);
+					s += nch;
+					SKIP_THth(s, n->suffix);
 				}
 				break;
 			case DCH_YYYY:
 			case DCH_IYYY:
 				from_char_parse_int(&out->year, &s, n);
 				out->yysz = 4;
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_YYY:
 			case DCH_IYY:
 				if (from_char_parse_int(&out->year, &s, n) < 4)
 					out->year = adjust_partial_year_to_2020(out->year);
 				out->yysz = 3;
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_YY:
 			case DCH_IY:
 				if (from_char_parse_int(&out->year, &s, n) < 4)
 					out->year = adjust_partial_year_to_2020(out->year);
 				out->yysz = 2;
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_Y:
 			case DCH_I:
 				if (from_char_parse_int(&out->year, &s, n) < 4)
 					out->year = adjust_partial_year_to_2020(out->year);
 				out->yysz = 1;
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_RM:
 				from_char_seq_search(&value, &s, rm_months_upper,
@@ -3206,11 +3200,11 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 				break;
 			case DCH_W:
 				from_char_parse_int(&out->w, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 			case DCH_J:
 				from_char_parse_int(&out->j, &s, n);
-				s += SKIP_THth(n->suffix);
+				SKIP_THth(s, n->suffix);
 				break;
 		}
 	}