From be79debd9688da516f49ba9b825ee2e784d1fab0 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 12 Apr 2021 11:31:26 +0900
Subject: [PATCH] Fix out-of-bound memory access for interval -> char
 conversion

Using Roman numbers (via "RM" or "rm") for a conversion to calculate a
number of months has never considered the case of negative numbers,
where a conversion could easily cause out-of-bound memory accesses.  The
conversions in themselves were not completely consistent either, as
specifying 12 would result in NULL, but it should mean XII.

This commit reworks the conversion calculation to have a more
consistent behavior:
- If the number of months and years is 0, return NULL.
- If the number of months is positive, return the exact month number.
- If the number of months is negative, do a backward calculation, with
-1 meaning December, -2 November, etc.

Reported-by: Theodor Arsenij Larionov-Trichkin
Author: Julien Rouhaud
Discussion: https://postgr.es/m/16953-f255a18f8c51f1d5@postgresql.org
backpatch-through: 9.6
---
 src/backend/utils/adt/formatting.c      | 63 +++++++++++++++++++++----
 src/test/regress/expected/timestamp.out | 36 ++++++++++++++
 src/test/regress/sql/timestamp.sql      |  6 +++
 3 files changed, 95 insertions(+), 10 deletions(-)

diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 67271ba3cb..f1a753fc91 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -3208,18 +3208,61 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				s += strlen(s);
 				break;
 			case DCH_RM:
-				if (!tm->tm_mon)
-					break;
-				sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -4,
-						rm_months_upper[MONTHS_PER_YEAR - tm->tm_mon]);
-				s += strlen(s);
-				break;
+				/* FALLTHROUGH */
 			case DCH_rm:
-				if (!tm->tm_mon)
+
+				/*
+				 * For intervals, values like '12 month' will be reduced to 0
+				 * month and some years.  These should be processed.
+				 */
+				if (!tm->tm_mon && !tm->tm_year)
 					break;
-				sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -4,
-						rm_months_lower[MONTHS_PER_YEAR - tm->tm_mon]);
-				s += strlen(s);
+				else
+				{
+					int			mon = 0;
+					const char *const *months;
+
+					if (n->key->id == DCH_RM)
+						months = rm_months_upper;
+					else
+						months = rm_months_lower;
+
+					/*
+					 * Compute the position in the roman-numeral array.  Note
+					 * that the contents of the array are reversed, December
+					 * being first and January last.
+					 */
+					if (tm->tm_mon == 0)
+					{
+						/*
+						 * This case is special, and tracks the case of full
+						 * interval years.
+						 */
+						mon = tm->tm_year >= 0 ? 0 : MONTHS_PER_YEAR - 1;
+					}
+					else if (tm->tm_mon < 0)
+					{
+						/*
+						 * Negative case.  In this case, the calculation is
+						 * reversed, where -1 means December, -2 November,
+						 * etc.
+						 */
+						mon = -1 * (tm->tm_mon + 1);
+					}
+					else
+					{
+						/*
+						 * Common case, with a strictly positive value.  The
+						 * position in the array matches with the value of
+						 * tm_mon.
+						 */
+						mon = MONTHS_PER_YEAR - tm->tm_mon;
+					}
+
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -4,
+							months[mon]);
+					s += strlen(s);
+				}
 				break;
 			case DCH_W:
 				sprintf(s, "%d", (tm->tm_mday - 1) / 7 + 1);
diff --git a/src/test/regress/expected/timestamp.out b/src/test/regress/expected/timestamp.out
index 5f97505a30..056b221aba 100644
--- a/src/test/regress/expected/timestamp.out
+++ b/src/test/regress/expected/timestamp.out
@@ -1703,6 +1703,42 @@ SELECT '' AS to_char_12, to_char(d, 'FF1 FF2 FF3 FF4 FF5 FF6  ff1 ff2 ff3 ff4 ff
             | 7 78 789 7890 78901 789012  7 78 789 7890 78901 789012  789 789012
 (4 rows)
 
+-- Roman months, with upper and lower case.
+SELECT i,
+       to_char(i * interval '1mon', 'rm'),
+       to_char(i * interval '1mon', 'RM')
+    FROM generate_series(-13, 13) i;
+  i  | to_char | to_char 
+-----+---------+---------
+ -13 | xii     | XII 
+ -12 | i       | I   
+ -11 | ii      | II  
+ -10 | iii     | III 
+  -9 | iv      | IV  
+  -8 | v       | V   
+  -7 | vi      | VI  
+  -6 | vii     | VII 
+  -5 | viii    | VIII
+  -4 | ix      | IX  
+  -3 | x       | X   
+  -2 | xi      | XI  
+  -1 | xii     | XII 
+   0 |         | 
+   1 | i       | I   
+   2 | ii      | II  
+   3 | iii     | III 
+   4 | iv      | IV  
+   5 | v       | V   
+   6 | vi      | VI  
+   7 | vii     | VII 
+   8 | viii    | VIII
+   9 | ix      | IX  
+  10 | x       | X   
+  11 | xi      | XI  
+  12 | xii     | XII 
+  13 | i       | I   
+(27 rows)
+
 -- timestamp numeric fields constructor
 SELECT make_timestamp(2014,12,28,6,30,45.887);
         make_timestamp        
diff --git a/src/test/regress/sql/timestamp.sql b/src/test/regress/sql/timestamp.sql
index 7b58c3cfa5..4f014dad45 100644
--- a/src/test/regress/sql/timestamp.sql
+++ b/src/test/regress/sql/timestamp.sql
@@ -239,5 +239,11 @@ SELECT '' AS to_char_12, to_char(d, 'FF1 FF2 FF3 FF4 FF5 FF6  ff1 ff2 ff3 ff4 ff
        ('2018-11-02 12:34:56.78901234')
    ) d(d);
 
+-- Roman months, with upper and lower case.
+SELECT i,
+       to_char(i * interval '1mon', 'rm'),
+       to_char(i * interval '1mon', 'RM')
+    FROM generate_series(-13, 13) i;
+
 -- timestamp numeric fields constructor
 SELECT make_timestamp(2014,12,28,6,30,45.887);