postgres.git / summary / log / commit / refs

commit    63a03aea6bc89060010255e8e61c83f95e1daec8
Author:   David Rowley <drowley@postgresql.org>
Date:     Thu Apr 20 22:02:25 2023 +0000
First released in: 16.0, 15.3

    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 75aa5baa807..90f93e893cf 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));
 


[parent: 94d73f9abdf1]