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From:   Takashi Iwai <tiwai@suse.de>
To:     Mauro Carvalho Chehab <mchehab@kernel.org>
Cc:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] media: dvb-core: Fix kernel WARNING for blocking operation in wait_event*()
Date:   Fri, 12 May 2023 17:18:00 +0200
Message-Id: <20230512151800.1874-1-tiwai@suse.de>
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Using a semaphore in the wait_event*() condition is no good idea.
It hits a kernel WARN_ON() at prepare_to_wait_event() like:
  do not call blocking ops when !TASK_RUNNING; state=1 set at
  prepare_to_wait_event+0x6d/0x690

For avoiding the potential deadlock, rewrite to an open-coded loop
instead.  Unlike the loop in wait_event*(), this uses wait_woken()
after the condition check, hence the task state stays consistent.

CVE-2023-31084 was assigned to this bug.

Reported-by: Yu Hao <yhao016@ucr.edu>
Link: https://lore.kernel.org/r/CA+UBctCu7fXn4q41O_3=id1+OdyQ85tZY1x+TkT-6OVBL6KAUw@mail.gmail.com/
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 drivers/media/dvb-core/dvb_frontend.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index cc0a789f09ae..9293b058ab99 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -293,14 +293,22 @@ static int dvb_frontend_get_event(struct dvb_frontend *fe,
 	}
 
 	if (events->eventw == events->eventr) {
-		int ret;
+		struct wait_queue_entry wait;
+		int ret = 0;
 
 		if (flags & O_NONBLOCK)
 			return -EWOULDBLOCK;
 
-		ret = wait_event_interruptible(events->wait_queue,
-					       dvb_frontend_test_event(fepriv, events));
-
+		init_waitqueue_entry(&wait, current);
+		add_wait_queue(&events->wait_queue, &wait);
+		while (!dvb_frontend_test_event(fepriv, events)) {
+			wait_woken(&wait, TASK_INTERRUPTIBLE, 0);
+			if (signal_pending(current)) {
+				ret = -ERESTARTSYS;
+				break;
+			}
+		}
+		remove_wait_queue(&events->wait_queue, &wait);
 		if (ret < 0)
 			return ret;
 	}
-- 
2.35.3