TIOCSSERIAL fixes

This series fixes up a few issues with cdc-acm TIOCSSERIAL implementation.

Johan

Changes in v2
- amend commit message to clarify that the 12 cs close_delay bug had already been fixed by an earlier patch (1/3)

- amend commit message to clarify that the base clock rate isn't known for CDC and that the current line speed can still be retrieved through the standard termios interfaces (3/3)

Johan Hovold (3):
Revert "USB: cdc-acm: fix rounding error in TIOCSSERIAL"
USB: cdc-acm: fix unprivileged TIOCCSERIAL
USB: cdc-acm: fix TIOCGSERIAL implementation

 drivers/usb/class/cdc-acm.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

2.26.3

This reverts commit b401f8c4f492cbf74f3f59c9141e5be3071071bb.

The offending commit claimed that trying to set the values reported back by TIOCGSERIAL as a regular user could result in an -EPERM error when HZ is 250, but that was never the case.

With HZ=250, the default 0.5 second value of close_delay is converted to 125 jiffies when set and is converted back to 50 centiseconds by TIOCGSERIAL as expected (not 12 cs as was claimed, even if that was the case before an earlier fix).

Comparing the internal current and new jiffies values is just fine to determine if the value is about to change so drop the bogus workaround (which was also backported to stable).

For completeness: With different default values for these parameters or with a HZ value not divisible by two, the lack of rounding when setting the default values in tty_port_init() could result in an -EPERM being returned, but this is hardly something we need to worry about.

---
 drivers/usb/class/cdc-acm.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

index 3fda1ec961d7..96e221803fa6 100644
@@ -942,7 +942,6 @@ 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);

@@ -950,17 +949,11 @@ 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 ((ss->close_delay != old_close_delay) ||
-		    (ss->closing_wait != old_closing_wait))
+		if ((close_delay != acm->port.close_delay) ||
+		    (closing_wait != acm->port.closing_wait))
 			retval = -EPERM;
 		else
 			retval = -EOPNOTSUPP;

2.26.3

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.

---
 drivers/usb/class/cdc-acm.c | 2 --
 1 file changed, 2 deletions(-)

index 96e221803fa6..43e31dad4831 100644
@@ -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

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.

The xmit_fifo_size parameter could be used to set the hardware transmit fifo size of a legacy UART when it could not be detected, but the interface is limited to eight bits and should be left unset when it is not used.

Similarly, baud_base could be used to set the UART base clock when it could not be detected, but might as well be left unset when it is not known (which is the case for CDC).

Fix the cdc-acm TIOCGSERIAL implementation by dropping its custom interpretation of the unused xmit_fifo_size and baud_base fields, which overflowed the former with the URB buffer size and set the latter to the current line speed. Also return the port line number, which is the only other value used besides the close parameters.

Note that the current line speed can still be retrieved through the standard termios interfaces.

---
 drivers/usb/class/cdc-acm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

index 43e31dad4831..b74713518b3a 100644
@@ -929,8 +929,7 @@ static int get_serial_info(struct tty_struct *tty, struct serial_struct *ss)
 {
 	struct acm *acm = tty->driver_data;
 
-	ss->xmit_fifo_size = acm->writesize;
-	ss->baud_base = le32_to_cpu(acm->line.dwDTERate);
+	ss->line = acm->minor;
 	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 :

2.26.3

Am Donnerstag, den 08.04.2021, 15:16 +0200 schrieb Johan Hovold: