4.17-stable review patch. If anyone has any objections, please let me know.
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From: Mauro Carvalho Chehab mchehab@s-opensource.com
commit 76d81243a487c09619822ef8e7201a756e58a87d upstream.
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@vger.kernel.org Signed-off-by: Mauro Carvalho Chehab mchehab@s-opensource.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/media/dvb-core/dvb_frontend.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-)
--- 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(struc 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 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;