From a6a35a2a03c2fecc1d6dbf552a262fa7321b7adf Mon Sep 17 00:00:00 2001 From: Alan Cox Date: Fri, 2 Jun 2017 13:49:30 +0100 Subject: tty: handle the case where we cannot restore a line discipline commit 8a8dabf2dd68caff842d38057097c23bc514ea6e upstream. Historically the N_TTY driver could never fail but this has become broken over time. Rather than trying to rewrite half the ldisc layer to fix the breakage introduce a second level of fallback with an N_NULL ldisc which cannot fail, and thus restore the guarantees required by the ldisc layer. We still try and fail to N_TTY first. It's much more useful to find yourself back in your old ldisc (first attempt) or in N_TTY (second attempt), and while I'm not aware of any code out there that makes those assumptions it's good to drive(r) defensively. Signed-off-by: Alan Cox Reported-by: Dmitry Vyukov Tested-by: Dmitry Vyukov Signed-off-by: Greg Kroah-Hartman [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings --- include/uapi/linux/tty.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/uapi/linux/tty.h b/include/uapi/linux/tty.h index dac199a2dba5..512892743489 100644 --- a/include/uapi/linux/tty.h +++ b/include/uapi/linux/tty.h @@ -34,5 +34,6 @@ #define N_TI_WL 22 /* for TI's WL BT, FM, GPS combo chips */ #define N_TRACESINK 23 /* Trace data routing for MIPI P1149.7 */ #define N_TRACEROUTER 24 /* Trace data routing for MIPI P1149.7 */ +#define N_NULL 27 /* Null ldisc used for error handling */ #endif /* _UAPI_LINUX_TTY_H */ -- cgit v1.2.3