linux-kernel - [PATCH 2/3] USB: cdc-acm: fix unprivileged TIOCCSERIAL

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Message-Id: <20210407102845.32720-3-johan@kernel.org>
Date:   Wed,  7 Apr 2021 12:28:44 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Oliver Neukum <oneukum@...e.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>
Subject: [PATCH 2/3] USB: cdc-acm: fix unprivileged TIOCCSERIAL

TIOCSSERIAL is a horrid, underspecified, legacy interface which for most
serial devices is only useful for setting the close_delay and
closing_wait parameters.

A non-privileged user has only ever been able to set the since long
deprecated ASYNC_SPD flags and trying to change any other *supported*
feature should result in -EPERM being returned. Setting the current
values for any supported features should return success.

Fix the cdc-acm implementation which instead indicated that the
TIOCSSERIAL ioctl was not even implemented when a non-privileged user
set the current values.

Fixes: ba2d8ce9db0a ("cdc-acm: implement TIOCSSERIAL to avoid blocking close(2)")
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/usb/class/cdc-acm.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 96e221803fa6..43e31dad4831 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -955,8 +955,6 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss)
 		if ((close_delay != acm->port.close_delay) ||
 		    (closing_wait != acm->port.closing_wait))
 			retval = -EPERM;
-		else
-			retval = -EOPNOTSUPP;
 	} else {
 		acm->port.close_delay  = close_delay;
 		acm->port.closing_wait = closing_wait;
-- 
2.26.3