netdev - [PATCH v2 net] net/sched: cls_api: fix possible infinite loop in tcf_idr_check

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Date: Thu, 13 Jun 2024 07:10:21 +0000
From: David Ruth <druth@...omium.org>
To: netdev@...r.kernel.org
Cc: jhs@...atatu.com,
	xiyou.wangcong@...il.com,
	jiri@...nulli.us,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	marcelo.leitner@...il.com,
	vladbu@...dia.com,
	David Ruth <druth@...omium.org>,
	syzbot+b87c222546179f4513a7@...kaller.appspotmail.com
Subject: [PATCH v2 net] net/sched: cls_api: fix possible infinite loop in tcf_idr_check_alloc()

syzbot found hanging tasks waiting on rtnl_lock [1]

A reproducer is available in the syzbot bug.

When a request to add multiple actions with the same index is sent, the
second request will block forever on the first request. This holds
rtnl_lock, and causes tasks to hang.

Return -EAGAIN to prevent infinite looping, while keeping documented
behavior.

[1]

INFO: task kworker/1:0:5088 blocked for more than 143 seconds.
Not tainted 6.9.0-rc4-syzkaller-00173-g3cdb45594619 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/1:0 state:D stack:23744 pid:5088 tgid:5088 ppid:2 flags:0x00004000
Workqueue: events_power_efficient reg_check_chans_work
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5409 [inline]
__schedule+0xf15/0x5d00 kernel/sched/core.c:6746
__schedule_loop kernel/sched/core.c:6823 [inline]
schedule+0xe7/0x350 kernel/sched/core.c:6838
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6895
__mutex_lock_common kernel/locking/mutex.c:684 [inline]
__mutex_lock+0x5b8/0x9c0 kernel/locking/mutex.c:752
wiphy_lock include/net/cfg80211.h:5953 [inline]
reg_leave_invalid_chans net/wireless/reg.c:2466 [inline]
reg_check_chans_work+0x10a/0x10e0 net/wireless/reg.c:2481

Fixes: 0190c1d452a9 ("net: sched: atomically check-allocate action")
Reported-by: syzbot+b87c222546179f4513a7@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b87c222546179f4513a7
Signed-off-by: David Ruth <druth@...omium.org>
---
V1 -> V2: Moved from net-next to net, identified the change this fixes

 net/sched/act_api.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 9ee622fb1160..2520708b06a1 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -830,7 +830,6 @@ int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index,
 	u32 max;

 	if (*index) {
-again:
 		rcu_read_lock();
 		p = idr_find(&idrinfo->action_idr, *index);

@@ -839,7 +838,7 @@ int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index,
 			 * index but did not assign the pointer yet.
 			 */
 			rcu_read_unlock();
-			goto again;
+			return -EAGAIN;
 		}

 		if (!p) {
-- 
2.45.2.627.g7a2c4fd464-goog