diff options
| author | Lukas Wunner <lukas@wunner.de> | 2021-11-22 18:58:24 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-11-25 20:41:09 +0300 |
| commit | f85e04503f369b3f2be28c83fc48b74e19936ebc (patch) | |
| tree | 30bca90e0cda698d093312a62b432a12d1dee947 /drivers/tty | |
| parent | 4e9679738a918d8a482ac6a2cb2bb871f094bb84 (diff) | |
| download | linux-f85e04503f369b3f2be28c83fc48b74e19936ebc.tar.xz | |
serial: 8250: Fix RTS modem control while in rs485 mode
Commit f45709df7731 ("serial: 8250: Don't touch RTS modem control while
in rs485 mode") sought to prevent user space from interfering with rs485
communication by ignoring a TIOCMSET ioctl() which changes RTS polarity.
It did so in serial8250_do_set_mctrl(), which turns out to be too deep
in the call stack: When a uart_port is opened, RTS polarity is set by
the rs485-aware function uart_port_dtr_rts(). It calls down to
serial8250_do_set_mctrl() and that particular RTS polarity change should
*not* be ignored.
The user-visible result is that on 8250_omap ports which use rs485 with
inverse polarity (RTS bit in MCR register is 1 to receive, 0 to send),
a newly opened port initially sets up RTS for sending instead of
receiving. That's because omap_8250_startup() sets the cached value
up->mcr to 0 and omap_8250_restore_regs() subsequently writes it to the
MCR register. Due to the commit, serial8250_do_set_mctrl() preserves
that incorrect register value:
do_sys_openat2
do_filp_open
path_openat
vfs_open
do_dentry_open
chrdev_open
tty_open
uart_open
tty_port_open
uart_port_activate
uart_startup
uart_port_startup
serial8250_startup
omap_8250_startup # up->mcr = 0
uart_change_speed
serial8250_set_termios
omap_8250_set_termios
omap_8250_restore_regs
serial8250_out_MCR # up->mcr written
tty_port_block_til_ready
uart_dtr_rts
uart_port_dtr_rts
serial8250_set_mctrl
omap8250_set_mctrl
serial8250_do_set_mctrl # mcr[1] = 1 ignored
Fix by intercepting RTS changes from user space in uart_tiocmset()
instead.
Link: https://lore.kernel.org/linux-serial/20211027111644.1996921-1-baocheng.su@siemens.com/
Fixes: f45709df7731 ("serial: 8250: Don't touch RTS modem control while in rs485 mode")
Cc: Chao Zeng <chao.zeng@siemens.com>
Cc: stable@vger.kernel.org # v5.7+
Reported-by: Su Bao Cheng <baocheng.su@siemens.com>
Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Tested-by: Su Bao Cheng <baocheng.su@siemens.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/21170e622a1aaf842a50b32146008b5374b3dd1d.1637596432.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/serial/8250/8250_port.c | 7 | ||||
| -rw-r--r-- | drivers/tty/serial/serial_core.c | 5 |
2 files changed, 5 insertions, 7 deletions
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 5775cbff8f6e..46e2079ad1aa 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2024,13 +2024,6 @@ void serial8250_do_set_mctrl(struct uart_port *port, unsigned int mctrl) struct uart_8250_port *up = up_to_u8250p(port); unsigned char mcr; - if (port->rs485.flags & SER_RS485_ENABLED) { - if (serial8250_in_MCR(up) & UART_MCR_RTS) - mctrl |= TIOCM_RTS; - else - mctrl &= ~TIOCM_RTS; - } - mcr = serial8250_TIOCM_to_MCR(mctrl); mcr = (mcr & up->mcr_mask) | up->mcr_force | up->mcr; diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 8968d15d7804..61e3dd0222af 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1075,6 +1075,11 @@ uart_tiocmset(struct tty_struct *tty, unsigned int set, unsigned int clear) goto out; if (!tty_io_error(tty)) { + if (uport->rs485.flags & SER_RS485_ENABLED) { + set &= ~TIOCM_RTS; + clear &= ~TIOCM_RTS; + } + uart_update_mctrl(uport, set, clear); ret = 0; } |