linux-kernel - [PATCH 5.11 274/601] USB: cdc-acm: fix unprivileged TIOCCSERIAL

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Date:   Wed, 12 May 2021 16:45:51 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Oliver Neukum <oneukum@...e.com>,
        Johan Hovold <johan@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.11 274/601] USB: cdc-acm: fix unprivileged TIOCCSERIAL

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

[ Upstream commit dd5619582d60007139f0447382d2839f4f9e339b ]

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)")
Acked-by: Oliver Neukum <oneukum@...e.com>
Signed-off-by: Johan Hovold <johan@...nel.org>
Link: https://lore.kernel.org/r/20210408131602.27956-3-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...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 0876468c2e7d..63824552e5d0 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;
-- 
2.30.2