media: imon: fix a race condition in send_packet()

The function send_packet() has a race condition as follows:

func send_packet()
{
    // do work
    call usb_submit_urb()
    mutex_unlock()
    wait_for_event_interruptible()  <-- lock gone
    mutex_lock()
}

func vfd_write()
{
    mutex_lock()
    call send_packet()  <- prev call is not completed
    mutex_unlock()
}

When the mutex is unlocked and the function send_packet() waits for the
call to complete, vfd_write() can start another call, which leads to the
"URB submitted while active" warning in usb_submit_urb().
Fix this by removing the mutex_unlock() call in send_packet() and using
mutex_lock_interruptible().

Link: https://syzkaller.appspot.com/bug?id=e378e6a51fbe6c5cc43e34f131cc9a315ef0337e
Fixes: 21677cfc562a ("V4L/DVB: ir-core: add imon driver")
Reported-by: syzbot+0c3cb6dc05fbbdc3ad66@syzkaller.appspotmail.com
Signed-off-by: Gautam Menghani <gautammenghani201@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
index 5edfd8a..74546f7 100644 (file)
--- a/drivers/media/rc/imon.c
+++ b/drivers/media/rc/imon.c
@@ -646,15 +646,14 @@ static int send_packet(struct imon_context *ictx)
                pr_err_ratelimited("error submitting urb(%d)\n", retval);
        } else {
                /* Wait for transmission to complete (or abort) */
-               mutex_unlock(&ictx->lock);
                retval = wait_for_completion_interruptible(
                                &ictx->tx.finished);
                if (retval) {
                        usb_kill_urb(ictx->tx_urb);
                        pr_err_ratelimited("task interrupted\n");
                }
-               mutex_lock(&ictx->lock);
 
+               ictx->tx.busy = false;
                retval = ictx->tx.status;
                if (retval)
                        pr_err_ratelimited("packet tx failed (%d)\n", retval);
@@ -953,7 +952,8 @@ static ssize_t vfd_write(struct file *file, const char __user *buf,
        if (ictx->disconnected)
                return -ENODEV;
 
-       mutex_lock(&ictx->lock);
+       if (mutex_lock_interruptible(&ictx->lock))
+               return -ERESTARTSYS;
 
        if (!ictx->dev_present_intf0) {
                pr_err_ratelimited("no iMON device present\n");