From: Anthony Mallet <anthony.mallet@xxxxxxx> [ Upstream commit b401f8c4f492cbf74f3f59c9141e5be3071071bb ] By default, tty_port_init() initializes those parameters to a multiple of HZ. For instance in line 69 of tty_port.c: port->close_delay = (50 * HZ) / 100; https://github.com/torvalds/linux/blob/master/drivers/tty/tty_port.c#L69 With e.g. CONFIG_HZ = 250 (as this is the case for Ubuntu 18.04 linux-image-4.15.0-37-generic), the default setting for close_delay is thus 125. When ioctl(fd, TIOCGSERIAL, &s) is executed, the setting returned in user space is '12' (125/10). When ioctl(fd, TIOCSSERIAL, &s) is then executed with the same setting '12', the value is interpreted as '120' which is different from the current setting and a EPERM error may be raised by set_serial_info() if !CAP_SYS_ADMIN. https://github.com/torvalds/linux/blob/master/drivers/usb/class/cdc-acm.c#L919 Fixes: ba2d8ce9db0a6 ("cdc-acm: implement TIOCSSERIAL to avoid blocking close(2)") Signed-off-by: Anthony Mallet <anthony.mallet@xxxxxxx> Cc: stable <stable@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20200312133101.7096-2-anthony.mallet@xxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/usb/class/cdc-acm.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 3cb7a23e1253f..7dd2f413595eb 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -857,6 +857,7 @@ static int set_serial_info(struct acm *acm, { struct serial_struct new_serial; unsigned int closing_wait, close_delay; + unsigned int old_closing_wait, old_close_delay; int retval = 0; if (copy_from_user(&new_serial, newinfo, sizeof(new_serial))) @@ -867,18 +868,24 @@ static int set_serial_info(struct acm *acm, ASYNC_CLOSING_WAIT_NONE : msecs_to_jiffies(new_serial.closing_wait * 10); + /* we must redo the rounding here, so that the values match */ + old_close_delay = jiffies_to_msecs(acm->port.close_delay) / 10; + old_closing_wait = acm->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ? + ASYNC_CLOSING_WAIT_NONE : + jiffies_to_msecs(acm->port.closing_wait) / 10; + mutex_lock(&acm->port.mutex); - if (!capable(CAP_SYS_ADMIN)) { - if ((close_delay != acm->port.close_delay) || - (closing_wait != acm->port.closing_wait)) + if ((new_serial.close_delay != old_close_delay) || + (new_serial.closing_wait != old_closing_wait)) { + if (!capable(CAP_SYS_ADMIN)) retval = -EPERM; - else - retval = -EOPNOTSUPP; - } else { - acm->port.close_delay = close_delay; - acm->port.closing_wait = closing_wait; - } + else { + acm->port.close_delay = close_delay; + acm->port.closing_wait = closing_wait; + } + } else + retval = -EOPNOTSUPP; mutex_unlock(&acm->port.mutex); return retval; -- 2.20.1
