From: Ben Kallus <benjamin.p.kallus.gr@dartmouth.edu>
Date: Wed, 29 Oct 2025 12:38:51 +0000 (-0400)
Subject: IMPORT: cebtree: Replace offset calculation with offsetof to avoid UB
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;ds=sidebyside;p=thirdparty%2Fhaproxy.git

IMPORT: cebtree: Replace offset calculation with offsetof to avoid UB

This is the same as the equivalent fix in ebtree:

The C standard specifies that it's undefined behavior to dereference
NULL (even if you use & right after). The hand-rolled offsetof idiom
&(((s*)NULL)->f) is thus technically undefined. This clutters the
output of UBSan and is simple to fix: just use the real offsetof when
it's available.

This is cebtree commit 2d08958858c2b8a1da880061aed941324e20e748.
---

diff --git a/include/import/cebtree-prv.h b/include/import/cebtree-prv.h
index 221968af5..e20bff0ca 100644
--- a/include/import/cebtree-prv.h
+++ b/include/import/cebtree-prv.h
@@ -555,7 +555,7 @@ struct ceb_node *_ceb_descend(struct ceb_root **root,
 	/* the parent will be the (possibly virtual) node so that
 	 * &lparent->l == root, i.e. container_of(root, struct ceb_node, b[0]).
 	 */
-	lparent = (struct ceb_node *)((char *)root - (long)&((struct ceb_node *)0)->b[0]);
+	lparent = (struct ceb_node *)((char *)root - offsetof(struct ceb_node, b));
 	gparent = lparent;
 	if (ret_nparent)
 		*ret_nparent = NULL;