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SubjectRe: [PATCH 4.19 094/133] USB: serial: iuu_phoenix: fix memory corruption
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.

We usually avoid subtle code by introducing comments, not by
introducing extra (and confusing) code that can not be optimized out.

Best regards,
Pavel
--
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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