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media: dvb_frontend: fix locking issues at dvb_frontend_get_event()

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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>
This commit is contained in:
Mauro Carvalho Chehab 2018-04-05 05:30:52 -04:00
parent 65c1167373
commit 76d81243a4
1 changed files with 15 additions and 8 deletions
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23
drivers/media/dvb-core/dvb_frontend.c
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@ -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;