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Subject: media: dvb_frontend: fix locking issues at dvb_frontend_get_event()
Author: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
Date: Thu Apr 5 05:30:52 2018 -0400
As warned by smatch:
drivers/media/dvb-core/dvb_frontend.c:314 dvb_frontend_get_event() warn: inconsistent returns 'sem:&fepriv->sem'.
Locked on: line 288
line 295
line 306
line 314
Unlocked on: line 303
The lock implementation for get event is wrong, as, if an
interrupt occurs, down_interruptible() will fail, and the
routine will call up() twice when userspace calls the ioctl
again.
The bad code is there since when Linux migrated to git, in
2005.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
drivers/media/dvb-core/dvb_frontend.c | 23 +++++++++++++++--------
1 file changed, 15 insertions(+), 8 deletions(-)
---
diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index e33414975065..a4ada1ccf0df 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -275,8 +275,20 @@ static void dvb_frontend_add_event(struct dvb_frontend *fe,
wake_up_interruptible (&events->wait_queue);
}
+static int dvb_frontend_test_event(struct dvb_frontend_private *fepriv,
+ struct dvb_fe_events *events)
+{
+ int ret;
+
+ up(&fepriv->sem);
+ ret = events->eventw != events->eventr;
+ down(&fepriv->sem);
+
+ return ret;
+}
+
static int dvb_frontend_get_event(struct dvb_frontend *fe,
- struct dvb_frontend_event *event, int flags)
+ struct dvb_frontend_event *event, int flags)
{
struct dvb_frontend_private *fepriv = fe->frontend_priv;
struct dvb_fe_events *events = &fepriv->events;
@@ -294,13 +306,8 @@ static int dvb_frontend_get_event(struct dvb_frontend *fe,
if (flags & O_NONBLOCK)
return -EWOULDBLOCK;
- up(&fepriv->sem);
-
- ret = wait_event_interruptible (events->wait_queue,
- events->eventw != events->eventr);
-
- if (down_interruptible (&fepriv->sem))
- return -ERESTARTSYS;
+ ret = wait_event_interruptible(events->wait_queue,
+ dvb_frontend_test_event(fepriv, events));
if (ret < 0)
return ret;