This is a note to let you know that I've just added the patch titled
USB: cdc-acm: fix rounding error in TIOCSSERIAL
to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From b401f8c4f492cbf74f3f59c9141e5be3071071bb Mon Sep 17 00:00:00 2001
From: Anthony Mallet <anthony.mallet@xxxxxxx>
Date: Thu, 12 Mar 2020 14:31:01 +0100
Subject: USB: cdc-acm: fix rounding error in TIOCSSERIAL
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>
---
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 da619176deca..47f09a6ce7bd 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;
mutex_unlock(&acm->port.mutex);
return retval;
--
2.25.1
