From: Anthony Mallet <anthony.mallet@laas.fr>
To: Oliver Neukum <oneukum@suse.com>, linux-usb@vger.kernel.org
Cc: Anthony Mallet <anthony.mallet@laas.fr>
Subject: [PATCH v4 2/2] USB: cdc-acm: fix rounding error in TIOCSSERIAL
Date: Thu, 12 Mar 2020 14:31:01 +0100 [thread overview]
Message-ID: <20200312133101.7096-2-anthony.mallet@laas.fr> (raw)
In-Reply-To: <20200312133101.7096-1-anthony.mallet@laas.fr>
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@laas.fr>
---
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;
mutex_unlock(&acm->port.mutex);
return retval;
--
2.17.1
next prev parent reply other threads:[~2020-03-12 13:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 13:31 [PATCH v4 1/2] USB: cdc-acm: fix close_delay and closing_wait units in TIOCSSERIAL Anthony Mallet
2020-03-12 13:31 ` Anthony Mallet [this message]
2020-03-27 12:37 ` [PATCH v4 2/2] USB: cdc-acm: fix rounding error " Matthias Reichl
2020-03-27 12:53 ` Greg Kroah-Hartman
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