On Tue, Jul 21, 2020 at 01:33:00PM +0200, Pavel Machek wrote: > Hi! > > > commit e7b931bee739e8a77ae216e613d3b99342b6dec0 upstream. > > > > The driver would happily overwrite its write buffer with user data in > > 256 byte increments due to a removed buffer-space sanity check. > > > +++ b/drivers/usb/serial/iuu_phoenix.c > > @@ -697,14 +697,16 @@ static int iuu_uart_write(struct tty_str > > struct iuu_private *priv = usb_get_serial_port_data(port); > > unsigned long flags; > > > > - if (count > 256) > > - return -ENOMEM; > > - > > spin_lock_irqsave(&priv->lock, flags); > > > > + count = min(count, 256 - priv->writelen); > > + if (count == 0) > > + goto out; > > + > > /* fill the buffer */ > > memcpy(priv->writebuf + priv->writelen, buf, count); > > priv->writelen += count; > > +out: > > spin_unlock_irqrestore(&priv->lock, flags); > > > > return count; > > Ok, so... goto and label is unneccessary, memcpy will do the right > thing with count == 0. That's generally too subtle. Better to clearly mark the error/exception path. > But what is worse, this changes return value in the error case; > returning 0 instead of -ENOMEM. I don't believe 0 is appropriate > return code here. > > (It should block on the write buffer if blocking or return -EAGAIN if > nonblocking, right?) No, zero is the correct return value here when the tty driver's buffer is full. The line discipline will then handle nonblocking writes correctly, etc. Johan
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