From 377b7a83007d277d32ef19f7c7590c8668d504cb Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 18 Mar 2021 22:09:41 -0400
Subject: [PATCH] Don't leak malloc'd strings when a GUC setting is rejected.

Because guc.c prefers to keep all its string values in malloc'd
not palloc'd storage, it has to be more careful than usual to
avoid leaks.  Error exits out of string GUC hook checks failed
to clear the proposed value string, and error exits out of
ProcessGUCArray() failed to clear the malloc'd results of
ParseLongOption().

Found via valgrind testing.
This problem is ancient, so back-patch to all supported branches.

Discussion: https://postgr.es/m/3816764.1616104288@sss.pgh.pa.us
---
 src/backend/utils/misc/guc.c | 75 +++++++++++++++++++++++-------------
 1 file changed, 49 insertions(+), 26 deletions(-)

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 5a3ca5b765..997b4b70ee 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -10773,6 +10773,8 @@ ProcessGUCArray(ArrayType *array,
 		char	   *s;
 		char	   *name;
 		char	   *value;
+		char	   *namecopy;
+		char	   *valuecopy;
 
 		d = array_ref(array, 1, &i,
 					  -1 /* varlenarray */ ,
@@ -10797,13 +10799,18 @@ ProcessGUCArray(ArrayType *array,
 			continue;
 		}
 
-		(void) set_config_option(name, value,
+		/* free malloc'd strings immediately to avoid leak upon error */
+		namecopy = pstrdup(name);
+		free(name);
+		valuecopy = pstrdup(value);
+		free(value);
+
+		(void) set_config_option(namecopy, valuecopy,
 								 context, source,
 								 action, true, 0, false);
 
-		free(name);
-		if (value)
-			free(value);
+		pfree(namecopy);
+		pfree(valuecopy);
 		pfree(s);
 	}
 }
@@ -11235,34 +11242,50 @@ static bool
 call_string_check_hook(struct config_string *conf, char **newval, void **extra,
 					   GucSource source, int elevel)
 {
+	volatile bool result = true;
+
 	/* Quick success if no hook */
 	if (!conf->check_hook)
 		return true;
 
-	/* Reset variables that might be set by hook */
-	GUC_check_errcode_value = ERRCODE_INVALID_PARAMETER_VALUE;
-	GUC_check_errmsg_string = NULL;
-	GUC_check_errdetail_string = NULL;
-	GUC_check_errhint_string = NULL;
-
-	if (!conf->check_hook(newval, extra, source))
+	/*
+	 * If elevel is ERROR, or if the check_hook itself throws an elog
+	 * (undesirable, but not always avoidable), make sure we don't leak the
+	 * already-malloc'd newval string.
+	 */
+	PG_TRY();
 	{
-		ereport(elevel,
-				(errcode(GUC_check_errcode_value),
-				 GUC_check_errmsg_string ?
-				 errmsg_internal("%s", GUC_check_errmsg_string) :
-				 errmsg("invalid value for parameter \"%s\": \"%s\"",
-						conf->gen.name, *newval ? *newval : ""),
-				 GUC_check_errdetail_string ?
-				 errdetail_internal("%s", GUC_check_errdetail_string) : 0,
-				 GUC_check_errhint_string ?
-				 errhint("%s", GUC_check_errhint_string) : 0));
-		/* Flush any strings created in ErrorContext */
-		FlushErrorState();
-		return false;
-	}
+		/* Reset variables that might be set by hook */
+		GUC_check_errcode_value = ERRCODE_INVALID_PARAMETER_VALUE;
+		GUC_check_errmsg_string = NULL;
+		GUC_check_errdetail_string = NULL;
+		GUC_check_errhint_string = NULL;
 
-	return true;
+		if (!conf->check_hook(newval, extra, source))
+		{
+			ereport(elevel,
+					(errcode(GUC_check_errcode_value),
+					 GUC_check_errmsg_string ?
+					 errmsg_internal("%s", GUC_check_errmsg_string) :
+					 errmsg("invalid value for parameter \"%s\": \"%s\"",
+							conf->gen.name, *newval ? *newval : ""),
+					 GUC_check_errdetail_string ?
+					 errdetail_internal("%s", GUC_check_errdetail_string) : 0,
+					 GUC_check_errhint_string ?
+					 errhint("%s", GUC_check_errhint_string) : 0));
+			/* Flush any strings created in ErrorContext */
+			FlushErrorState();
+			result = false;
+		}
+	}
+	PG_CATCH();
+	{
+		free(*newval);
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+
+	return result;
 }
 
 static bool