2021-04-08 13:18:19

by Johan Hovold

Subject: [PATCH v2 2/3] USB: cdc-acm: fix unprivileged TIOCCSERIAL

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)")
Signed-off-by: Johan Hovold <[email protected]>
---
drivers/usb/class/cdc-acm.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 96e221803fa6..43e31dad4831 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -955,8 +955,6 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss)
if ((close_delay != acm->port.close_delay) ||
(closing_wait != acm->port.closing_wait))
retval = -EPERM;
- else
- retval = -EOPNOTSUPP;
} else {
acm->port.close_delay = close_delay;
acm->port.closing_wait = closing_wait;
--
2.26.3

2021-04-08 13:34:09

by Oliver Neukum

Subject: Re: [PATCH v2 2/3] USB: cdc-acm: fix unprivileged TIOCCSERIAL

Am Donnerstag, den 08.04.2021, 15:16 +0200 schrieb Johan Hovold:
> 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)")
> Signed-off-by: Johan Hovold <[email protected]>
Acked-by: Oliver Neukum <[email protected]>