[PATCH] gc: fix cast in compare_tasks_by_selection()

From: "René Scharfe" <l.s.r@web.de>
To: Git Mailing List <git@vger.kernel.org>
Cc: Derrick Stolee <dstolee@microsoft.com>,
	Junio C Hamano <gitster@pobox.com>
Subject: [PATCH] gc: fix cast in compare_tasks_by_selection()
Date: Tue, 17 Nov 2020 22:59:49 +0100	[thread overview]
Message-ID: <d80423b7-c89d-99a2-ce49-8308822f7769@web.de> (raw)

compare_tasks_by_selection() is used with QSORT and gets passed pointers
to the elements of "static struct maintenance_task tasks[]".  It casts
the *addresses* of these passed pointers to element pointers, though,
and thus effectively compares some unrelated values from the stack.  Fix
the casts to actually compare array elements.

Detected by USan (make SANITIZE=undefined test).

Signed-off-by: René Scharfe <l.s.r@web.de>
---
 builtin/gc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 5cd2a43f9f..986b760b30 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1213,10 +1213,8 @@ static struct maintenance_task tasks[] = {

 static int compare_tasks_by_selection(const void *a_, const void *b_)
 {
-	const struct maintenance_task *a, *b;
-
-	a = (const struct maintenance_task *)&a_;
-	b = (const struct maintenance_task *)&b_;
+	const struct maintenance_task *a = a_;
+	const struct maintenance_task *b = b_;

 	return b->selected_order - a->selected_order;
 }
--
2.29.2
