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Fix list_copy_head() with empty Lists

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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
This commit is contained in:
David Rowley 2023-04-21 10:02:25 +12:00
parent 94d73f9abd
commit 63a03aea6b
1 changed files with 3 additions and 3 deletions
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6
src/backend/nodes/list.c
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@ -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));