[PATCH 4.19 050/115] media: cec: avoid decrementing transmit_queue_sz if it is 0

Greg Kroah-Hartman
2020-01-07T21:07:18Z

From: Hans Verkuil <hverkuil-cisco@xs4all.nl>

commit 95c29d46ab2a517e4c26d0a07300edca6768db17 upstream.

WARN if transmit_queue_sz is 0 but do not decrement it.
The CEC adapter will become unresponsive if it goes below
0 since then it thinks there are 4 billion messages in the
queue.

Obviously this should not happen, but a driver bug could
cause this.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: <stable@vger.kernel.org> # for v4.12 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/media/cec/cec-adap.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

--- a/drivers/media/cec/cec-adap.c
+++ b/drivers/media/cec/cec-adap.c
@@ -365,7 +365,8 @@ static void cec_data_cancel(struct cec_d
} else {
list_del_init(&data->list);
if (!(data->msg.tx_status & CEC_TX_STATUS_OK))
- data->adap->transmit_queue_sz--;
+ if (!WARN_ON(!data->adap->transmit_queue_sz))
+ data->adap->transmit_queue_sz--;
}

if (data->msg.tx_status & CEC_TX_STATUS_OK) {
@@ -417,6 +418,14 @@ static void cec_flush(struct cec_adapter
* need to do anything special in that case.
*/
}
+ /*
+ * If something went wrong and this counter isn't what it should
+ * be, then this will reset it back to 0. Warn if it is not 0,
+ * since it indicates a bug, either in this framework or in a
+ * CEC driver.
+ */
+ if (WARN_ON(adap->transmit_queue_sz))
+ adap->transmit_queue_sz = 0;
}

/*
@@ -507,7 +516,8 @@ int cec_thread_func(void *_adap)
data = list_first_entry(&adap->transmit_queue,
struct cec_data, list);
list_del_init(&data->list);
- adap->transmit_queue_sz--;
+ if (!WARN_ON(!data->adap->transmit_queue_sz))
+ adap->transmit_queue_sz--;

/* Make this the current transmitting message */
adap->transmitting = data;