Johannes Berg 59fba11d64 netlink: disable IRQs for netlink_lock_table() ... [ Upstream commit 1d482e666b ] Syzbot reports that in mac80211 we have a potential deadlock between our "local->stop_queue_reasons_lock" (spinlock) and netlink's nl_table_lock (rwlock). This is because there's at least one situation in which we might try to send a netlink message with this spinlock held while it is also possible to take the spinlock from a hardirq context, resulting in the following deadlock scenario reported by lockdep: CPU0 CPU1 ---- ---- lock(nl_table_lock); local_irq_disable(); lock(&local->queue_stop_reason_lock); lock(nl_table_lock); <Interrupt> lock(&local->queue_stop_reason_lock); This seems valid, we can take the queue_stop_reason_lock in any kind of context ("CPU0"), and call ieee80211_report_ack_skb() with the spinlock held and IRQs disabled ("CPU1") in some code path (ieee80211_do_stop() via ieee80211_free_txskb()). Short of disallowing netlink use in scenarios like these (which would be rather complex in mac80211's case due to the deep callchain), it seems the only fix for this is to disable IRQs while nl_table_lock is held to avoid hitting this scenario, this disallows the "CPU0" portion of the reported deadlock. Note that the writer side (netlink_table_grab()) already disables IRQs for this lock. Unfortunately though, this seems like a huge hammer, and maybe the whole netlink table locking should be reworked. Reported-by: syzbot+69ff9dff50dcfe14ddd4@syzkaller.appspotmail.com Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Sasha Levin <sashal@kernel.org>		2021-06-16 11:54:57 +02:00
..
af_netlink.c	netlink: disable IRQs for netlink_lock_table()	2021-06-16 11:54:57 +02:00
af_netlink.h	af_netlink: ensure that NLMSG_DONE never fails in dumps	2017-11-13 10:17:13 +09:00
diag.c	rhashtable: Change rhashtable_walk_start to return void	2017-12-11 09:58:38 -05:00
genetlink.c	genetlink: remove genl_bind	2020-07-22 09:31:58 +02:00
Kconfig	netlink: remove mmapped netlink support	2016-02-18 11:42:18 -05:00
Makefile