On Fri, Mar 27, 2020 at 01:37:24PM +0100, Matthias Reichl wrote: > On Thu, Mar 12, 2020 at 02:31:01PM +0100, Anthony Mallet wrote: > > 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> > > --- > > Changed in v2: fix typo (extra closing brace) > > Changed in v3: version this patch series > > Changed in v4: diffed against e6e6ec4 from github.com/torvalds/linux.git > > --- > > drivers/usb/class/cdc-acm.c | 27 +++++++++++++++++---------- > > 1 file changed, 17 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c > > index da619176deca..a41a3d27016c 100644 > > --- a/drivers/usb/class/cdc-acm.c > > +++ b/drivers/usb/class/cdc-acm.c > > @@ -907,6 +907,7 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss) > > { > > struct acm *acm = tty->driver_data; > > unsigned int closing_wait, close_delay; > > + unsigned int old_closing_wait, old_close_delay; > > int retval = 0; > > > > close_delay = msecs_to_jiffies(ss->close_delay * 10); > > @@ -914,18 +915,24 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss) > > ASYNC_CLOSING_WAIT_NONE : > > msecs_to_jiffies(ss->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 ((ss->close_delay != old_close_delay) || > > + (ss->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; > > Swapping the order of the capability / close settings checks introduced > a rather unexpected regression: when running with CAP_SYS_ADMIN we now > get -EOPNOTSUPP when the close settings are unchanged. > > This will break programs / scripts that set these settings to fixed > values. > > eg (tested on vanilla 5.4.28) changing the settings works, but > setting the same value again fails: > > # setserial -a /dev/ttyACM0 > /dev/ttyACM0, Line 0, UART: unknown, Port: 0x0000, IRQ: 0 > Baud_base: 9600, close_delay: 50, divisor: 0 > closing_wait: 3000 > Flags: spd_normal > > # setserial /dev/ttyACM0 closing_wait 2000 > # setserial /dev/ttyACM0 closing_wait 2000 > Cannot set serial info: Operation not supported > > >From the commit message it's not clear why this behaviour was changed > so I suspect this might be a bug. Looks like a bug :( Care to send a patch to fix this up? thanks, greg k-h
