USB: cdc-acm: fix unprivileged TIOCCSERIAL

[ 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@suse.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210408131602.27956-3-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 8c476a785360ffbfd0112de1fdd321e68160d74d..0478d55bd283841253c179828c8a256200046d2b 100644 (file)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -883,8 +883,6 @@ static int set_serial_info(struct acm *acm,
                if ((new_serial.close_delay != old_close_delay) ||
                    (new_serial.closing_wait != old_closing_wait))
                        retval = -EPERM;
-               else
-                       retval = -EOPNOTSUPP;
        } else {
                acm->port.close_delay  = close_delay;
                acm->port.closing_wait = closing_wait;