From eae09137d53ecb9cb4c1ba7624723f1c1cbebeec Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 1 Mar 2023 11:30:17 -0500
Subject: [PATCH] Avoid fetching one past the end of translate()'s "to"
 parameter.

This is usually harmless, but if you were very unlucky it could
provoke a segfault due to the "to" string being right up against
the end of memory.  Found via valgrind testing (so we might've
found it earlier, except that our regression tests lacked any
exercise of translate()'s deletion feature).

Fix by switching the order of the test-for-end-of-string and
advance-pointer steps.  While here, compute "to_ptr + tolen"
just once.  (Smarter compilers might figure that out for
themselves, but let's just make sure.)

Report and fix by Daniil Anisimov, in bug #17816.

Discussion: https://postgr.es/m/17816-70f3d2764e88a108@postgresql.org
---
 src/backend/utils/adt/oracle_compat.c | 12 +++++++-----
 src/test/regress/expected/strings.out |  6 ++++++
 src/test/regress/sql/strings.sql      |  1 +
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/backend/utils/adt/oracle_compat.c b/src/backend/utils/adt/oracle_compat.c
index 018e8c93428..6a5ce1cc102 100644
--- a/src/backend/utils/adt/oracle_compat.c
+++ b/src/backend/utils/adt/oracle_compat.c
@@ -800,7 +800,8 @@ translate(PG_FUNCTION_ARGS)
 	text	   *to = PG_GETARG_TEXT_PP(2);
 	text	   *result;
 	char	   *from_ptr,
-			   *to_ptr;
+			   *to_ptr,
+			   *to_end;
 	char	   *source,
 			   *target;
 	int			m,
@@ -822,6 +823,7 @@ translate(PG_FUNCTION_ARGS)
 	from_ptr = VARDATA_ANY(from);
 	tolen = VARSIZE_ANY_EXHDR(to);
 	to_ptr = VARDATA_ANY(to);
+	to_end = to_ptr + tolen;
 
 	/*
 	 * The worst-case expansion is to substitute a max-length character for a
@@ -856,16 +858,16 @@ translate(PG_FUNCTION_ARGS)
 		}
 		if (i < fromlen)
 		{
-			/* substitute */
+			/* substitute, or delete if no corresponding "to" character */
 			char	   *p = to_ptr;
 
 			for (i = 0; i < from_index; i++)
 			{
-				p += pg_mblen(p);
-				if (p >= (to_ptr + tolen))
+				if (p >= to_end)
 					break;
+				p += pg_mblen(p);
 			}
-			if (p < (to_ptr + tolen))
+			if (p < to_end)
 			{
 				len = pg_mblen(p);
 				memcpy(target, p, len);
diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index 0f95b9400b6..b72120d48b2 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -2506,6 +2506,12 @@ SELECT translate('12345', '14', 'ax');
  a23x5
 (1 row)
 
+SELECT translate('12345', '134', 'a');
+ translate 
+-----------
+ a25
+(1 row)
+
 SELECT ascii('x');
  ascii 
 -------
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index 8c379182cb9..fd4f1f674aa 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -813,6 +813,7 @@ SELECT ltrim('zzzytrim', 'xyz');
 
 SELECT translate('', '14', 'ax');
 SELECT translate('12345', '14', 'ax');
+SELECT translate('12345', '134', 'a');
 
 SELECT ascii('x');
 SELECT ascii('');