linux-kernel - [PATCH 3.16 040/328] tty: fix termios input-speed encoding when using BOTHER

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Message-ID: <lsq.1544392233.519857667@decadent.org.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Johan Hovold" <johan@...nel.org>
Subject: [PATCH 3.16 040/328] tty: fix termios input-speed encoding when
 using BOTHER

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@...nel.org>

commit 1cee38f0363a88db374e50b232ca17b9a4c12fa0 upstream.

When the termios CIBAUD bits are left unset (i.e. B0), we use the same
output and input speed and should leave CIBAUD unchanged.

When the user requests a rate using BOTHER and c_ospeed which the driver
cannot set exactly, the driver can report back the actual baud rate
using tty_termios_encode_baud_rate(). If this rate is close enough to a
standard rate however, we could end up setting CIBAUD to a Bfoo value
despite the user having left it unset.

This in turn could lead to an unexpected input rate being set on
subsequent termios updates.

Fix this by using a zero tolerance value also for the input rate when
CIBAUD is clear so that the matching logic works as expected.

Fixes: 78137e3b34e1 ("[PATCH] tty: improve encode_baud_rate logic")
Signed-off-by: Johan Hovold <johan@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/tty/tty_ioctl.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -407,16 +407,20 @@ void tty_termios_encode_baud_rate(struct
 	termios->c_ospeed = obaud;

 #ifdef BOTHER
+	if ((termios->c_cflag >> IBSHIFT) & CBAUD)
+		ibinput = 1;	/* An input speed was specified */
+
 	/* If the user asked for a precise weird speed give a precise weird
 	   answer. If they asked for a Bfoo speed they may have problems
 	   digesting non-exact replies so fuzz a bit */

-	if ((termios->c_cflag & CBAUD) == BOTHER)
+	if ((termios->c_cflag & CBAUD) == BOTHER) {
 		oclose = 0;
+		if (!ibinput)
+			iclose = 0;
+	}
 	if (((termios->c_cflag >> IBSHIFT) & CBAUD) == BOTHER)
 		iclose = 0;
-	if ((termios->c_cflag >> IBSHIFT) & CBAUD)
-		ibinput = 1;	/* An input speed was specified */
 #endif
 	termios->c_cflag &= ~CBAUD;
 #ifdef IBSHIFT