Am Donnerstag, den 05.03.2020, 11:24 +0100 schrieb Anthony Mallet: > 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 > > Signed-off-by: Anthony Mallet <anthony.mallet@xxxxxxx> > Fixes: ba2d8ce9db0a6 ("cdc-acm: implement TIOCSSERIAL to avoid blocking close(2)") Acked-by: Oliver Neukum <oneukum@xxxxxxxx> Regards Oliver
