Lukas Wunner a5d0a72b80 serial: 8250: Fix RTS modem control while in rs485 mode ... commit f85e04503f369b3f2be28c83fc48b74e19936ebc upstream. Commit f45709df77 ("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: f45709df77 ("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>		2021-12-08 09:03:29 +01:00
..
hvc	tty: hvc: replace BUG_ON() with negative return value	2021-12-01 09:19:10 +01:00
ipwireless
serdev
serial	serial: 8250: Fix RTS modem control while in rs485 mode	2021-12-08 09:03:29 +01:00
vt	tty: Fix out-of-bound vmalloc access in imageblit	2021-10-06 15:55:45 +02:00
amiserial.c
cyclades.c
ehv_bytechan.c
goldfish.c
isicom.c
Kconfig
Makefile
mips_ejtag_fdc.c
moxa.c
moxa.h
mxser.c
mxser.h
n_gsm.c
n_hdlc.c
n_null.c
n_r3964.c
n_tracerouter.c
n_tracesink.c
n_tracesink.h
n_tty.c
nozomi.c	tty: nozomi: Fix the error handling path of 'nozomi_card_init()'	2021-07-14 16:56:39 +02:00
pty.c
rocket_int.h
rocket.c
rocket.h
synclink_gt.c	tty: synclink_gt: rename a conflicting function name	2021-09-30 10:11:03 +02:00
synclink.c
synclinkmp.c
sysrq.c
tty_audit.c
tty_baudrate.c
tty_buffer.c	tty: tty_buffer: Fix the softlockup issue in flush_to_ldisc	2021-11-26 10:39:10 +01:00
tty_io.c	tty: Fix data race between tiocsti() and flush_to_ldisc()	2021-09-15 09:50:47 +02:00
tty_ioctl.c
tty_jobctrl.c
tty_ldisc.c
tty_ldsem.c
tty_mutex.c
tty_port.c
ttynull.c
vcc.c