6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dmitry Antipov <dmantipov@xxxxxxxxx>
[ Upstream commit f504465970aebb2467da548f7c1efbbf36d0f44b ]
In 'taprio_change()', 'admin' pointer may become dangling due to sched
switch / removal caused by 'advance_sched()', and critical section
protected by 'q->current_entry_lock' is too small to prevent from such
a scenario (which causes use-after-free detected by KASAN). Fix this
by prefer 'rcu_replace_pointer()' over 'rcu_assign_pointer()' to update
'admin' immediately before an attempt to schedule freeing.
Fixes: a3d43c0d56f1 ("taprio: Add support adding an admin schedule")
Reported-by: syzbot+b65e0af58423fc8a73aa@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=b65e0af58423fc8a73aa
Acked-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
Link: https://patch.msgid.link/20241018051339.418890-1-dmantipov@xxxxxxxxx
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/sched/sch_taprio.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 87090d6790362..bc8e55c6d63d1 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1988,7 +1988,8 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
taprio_start_sched(sch, start, new_admin);
- rcu_assign_pointer(q->admin_sched, new_admin);
+ admin = rcu_replace_pointer(q->admin_sched, new_admin,
+ lockdep_rtnl_is_held());
if (admin)
call_rcu(&admin->rcu, taprio_free_sched_cb);
--
2.43.0
