From e35ded29566f679e52888a8d34468bb51bc78bed Mon Sep 17 00:00:00 2001 From: David Rowley Date: Thu, 20 Apr 2023 10:34:46 +1200 Subject: [PATCH] Fix list_copy_head() with empty Lists list_copy_head() given an empty List would crash from trying to dereference the List to obtain its length. Since NIL is how we represent an empty List, we should just be returning another empty List in this case. list_copy_head() is new to v16, so let's fix it now before too many people start coding around the buggy NIL behavior. Reported-by: Miroslav Bendik Discussion: https://postgr.es/m/CAPoEpV02WhawuWnmnKet6BqU63bEu7oec0pJc=nKMtPsHMzTXQ@mail.gmail.com --- src/backend/nodes/list.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/src/backend/nodes/list.c b/src/backend/nodes/list.c index a709d23ef1..750ee5a7e5 100644 --- a/src/backend/nodes/list.c +++ b/src/backend/nodes/list.c @@ -1593,11 +1593,11 @@ list_copy_head(const List *oldlist, int len) { List *newlist; - len = Min(oldlist->length, len); - - if (len <= 0) + if (oldlist == NIL || len <= 0) return NIL; + len = Min(oldlist->length, len); + newlist = new_list(oldlist->type, len); memcpy(newlist->elements, oldlist->elements, len * sizeof(ListCell));