staging: fwserial: fix TIOCSSERIAL implementation

stable inclusion
from stable-5.10.37
commit e08a24ae25b325ecb443340f290d3ff6418b7560
bugzilla: 51868
CVE: NA

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

[ Upstream commit a7eaaa9d ]

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 fwserial implementation which was returning -EPERM also for a
privileged user when trying to change certain unsupported parameters,
and instead return success consistently.

Fixes: 7355ba34 ("staging: fwserial: Add TTY-over-Firewire serial driver")
Signed-off-by: NJohan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407102334.32361-4-johan@kernel.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/staging/fwserial/fwserial.c

@@ -1234,10 +1234,6 @@ static int set_serial_info(struct tty_struct *tty,
 	struct fwtty_port *port = tty->driver_data;
 	unsigned int cdelay;
 
-	if (ss->irq != 0 || ss->port != 0 || ss->custom_divisor != 0 ||
-	    ss->baud_base != 400000000)
-		return -EPERM;
-
 	cdelay = msecs_to_jiffies(ss->close_delay * 10);
 
 	mutex_lock(&port->port.mutex);