linux-kernel - hci_ldisc: suspicious/buggy code

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Message-ID: <20161017213205.GA25141@amd>
Date:   Mon, 17 Oct 2016 23:32:06 +0200
From:   Pavel Machek <pavel@....cz>
To:     ifaenson@...adcom.com, marcel@...tmann.org,
        kernel list <linux-kernel@...r.kernel.org>,
        gustavo@...ovan.org, johan.hedberg@...il.com,
        linux-bluetooth@...r.kernel.org, sre@...nel.org
Subject: hci_ldisc: suspicious/buggy code

Hi!

hci_uart_set_flow_control() contains some rather suspicious
code. AFAICT:

set = 0.

Then we do set &= (magic constant). But as set is 0, it stays zero. It
just does not make sense. [Nor does it make sense to do |= on known
value of zero just after else. But that's probably just some artifact
of editing.]

(And if you edit the code anyway, temporary variable to store
TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 | TIOCM_OUT2 | TIOCM_LOOP would
make sense.)

Thanks,
								Pavel


/* Flow control or un-flow control the device */
void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
{
	...
	unsigned int set = 0;
	unsigned int clear = 0;

	if (enable) {
	   	...
		set &= ~(TIOCM_OUT2 | TIOCM_RTS);
		clear = ~set;
		set &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
		       TIOCM_OUT2 | TIOCM_LOOP;
		clear &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
			 TIOCM_OUT2 | TIOCM_LOOP;
		status = tty->driver->ops->tiocmset(tty, set, clear);
		BT_DBG("Clearing RTS: %s", status ? "failed" : "success");
	} else {
	       ...	
		set |= (TIOCM_OUT2 | TIOCM_RTS);

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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