On Wednesday 19 Feb 2020, at 10:56, Oliver Neukum wrote: > thank you for the detailed report about an unusual bug. Could you > test the attached patch? I did not actually run it yet, but at first sight it seems that it will mishandle the ASYNC_CLOSING_WAIT_NONE case. I attach patch 0002 which should handle all cases. I also inverted the logic of the CAP_SYS_ADMIN test, so that the delays are changed only if the rounded values (in 1/100th of seconds) are actually changed. While I was there, I checked what other drivers do (it seems that many have the same issue). Something I also noticed is that the units are also maybe mishandled: internally the values seem to be in 'jiffies', not in msecs. See for instance: https://github.com/torvalds/linux/blob/701a9c8092ddf299d7f90ab2d66b19b4526d1186/drivers/tty/serial/serial_core.c#L780 So I added patch 0001 that uses the jiffies conversion functions. If you prefer to discuss this in a separate thread please tell me, I will redo just patch 0002 without this change. > I have taken the liberty of presuming to add your 'Reported-and-tested-by'. Yes, no problem. Thank you. I hope my patches follow the required format, I'm not sure about all the details. Regards, Anthony
>From 3bc102eaa325fec8c181a51853ce3168dd89befa Mon Sep 17 00:00:00 2001 From: Anthony Mallet <anthony.mallet@xxxxxxx> Date: Wed, 19 Feb 2020 11:39:12 +0100 Subject: [PATCH 1/2] USB: cdc-acm: fix close_delay and closing_wait units in TIOCSSERIAL close_delay and closing_wait are specified in hundredth of a second but stored internally in jiffies. Use the jiffies_to_msecs() and msecs_to_jiffies() functions to convert from each other. Reported-and-tested-by: Anthony Mallet <anthony.mallet@xxxxxxx> --- drivers/usb/class/cdc-acm.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 62f4fb9b3..da619176d 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -896,10 +896,10 @@ static int get_serial_info(struct tty_struct *tty, struct serial_struct *ss) ss->xmit_fifo_size = acm->writesize; ss->baud_base = le32_to_cpu(acm->line.dwDTERate); - ss->close_delay = acm->port.close_delay / 10; + ss->close_delay = jiffies_to_msecs(acm->port.close_delay) / 10; ss->closing_wait = acm->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ? ASYNC_CLOSING_WAIT_NONE : - acm->port.closing_wait / 10; + jiffies_to_msecs(acm->port.closing_wait) / 10; return 0; } @@ -909,9 +909,10 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss) unsigned int closing_wait, close_delay; int retval = 0; - close_delay = ss->close_delay * 10; + close_delay = msecs_to_jiffies(ss->close_delay * 10); closing_wait = ss->closing_wait == ASYNC_CLOSING_WAIT_NONE ? - ASYNC_CLOSING_WAIT_NONE : ss->closing_wait * 10; + ASYNC_CLOSING_WAIT_NONE : + msecs_to_jiffies(ss->closing_wait * 10); mutex_lock(&acm->port.mutex); -- 2.17.1
>From 448f387419a5970021b096248aa8650d8c03392d Mon Sep 17 00:00:00 2001 From: Anthony Mallet <anthony.mallet@xxxxxxx> Date: Wed, 19 Feb 2020 11:47:03 +0100 Subject: [PATCH 2/2] USB: cdc-acm: fix rounding error in TIOCSSERIAL Quoting the bug reporter: 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 Reported-and-tested-by: Anthony Mallet <anthony.mallet@xxxxxxx> Fixes: ba2d8ce9db0a6 ("cdc-acm: implement TIOCSSERIAL to avoid blocking close(2)") --- 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 da619176d..b43820fb2 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; @@ -969,7 +976,7 @@ static int wait_serial_change(struct acm *acm, unsigned long arg) } } while (!rv); - + return rv; } -- 2.17.1
