Hi, Hackers!
In the AQO project (Adaptive Query Optimization) [1] the nodeToString()
function is used by the planner to convert an query parse tree into a
string to generate a hash value [2].
In PostgreSQL v.11 call nodeToString(parse) segfaulted.
The reason is: parse tree node for XMLNAMESPACES clause has null pointer
in the case of DEFAULT namespace (the pointer will be initialized at
executor on the first call). Function _outValue() uses value->val.str[0]
[3] without checking of value->val.str.
I want to know, which of next options is correct:
1. Converting a parse tree into string with nodeToString() is illegal
operation. We need to add a comment to the description of nodeToString().
2. We can use nodeToString() for parse tree convertation. In this case
we need to check node variable 'value->val.str' to NULL pointer (Now I
use this approach, see attachment).
[1] https://github.com/postgrespro/aqo
[2] hash.c, line 55.
[3] outfuncs.c, line 3312.
--
Andrey Lepikhov
Postgres Professional
https://postgrespro.com
The Russian Postgres Company
>From 26bfe91a4901b3b342e1b3ed58252ac750773207 Mon Sep 17 00:00:00 2001
From: "Andrey V. Lepikhov" <a.lepik...@postgrespro.ru>
Date: Sun, 16 Sep 2018 08:30:19 +0500
Subject: [PATCH] XML Bug fix
---
src/backend/nodes/outfuncs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 744a8b91b8..20eb033eac 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -3310,7 +3310,7 @@ _outValue(StringInfo str, const Value *value)
* but we don't want it to do anything with an empty string.
*/
appendStringInfoChar(str, '"');
- if (value->val.str[0] != '\0')
+ if ((value->val.str) && (value->val.str[0] != '\0'))
outToken(str, value->val.str);
appendStringInfoChar(str, '"');
break;
--
2.17.1
