From 63a03aea6bc89060010255e8e61c83f95e1daec8 Mon Sep 17 00:00:00 2001 From: David Rowley Date: Fri, 21 Apr 2023 10:02:25 +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 75aa5baa80..90f93e893c 100644 --- a/src/backend/nodes/list.c +++ b/src/backend/nodes/list.c @@ -1553,11 +1553,11 @@ 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));