serial: do not accept sysrq characters via serial port

many embedded boards have a disconnected TTL level serial which can
generate some garbage that can lead to spurious false sysrq detects.

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 5def8e8..58484fb 100644 (file)
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -450,7 +450,7 @@ extern void uart_handle_cts_change(struct uart_port *uport,
 extern void uart_insert_char(struct uart_port *port, unsigned int status,
                 unsigned int overrun, unsigned int ch, unsigned int flag);
 
-#ifdef SUPPORT_SYSRQ
+#if defined(SUPPORT_SYSRQ) && defined(CONFIG_MAGIC_SYSRQ_SERIAL)
 static inline int
 uart_handle_sysrq_char(struct uart_port *port, unsigned int ch)
 {

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b06848a..9fa4e6e 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -416,6 +416,16 @@ config MAGIC_SYSRQ_DEFAULT_ENABLE
          This may be set to 1 or 0 to enable or disable them all, or
          to a bitmask as described in Documentation/sysrq.txt.
 
+config MAGIC_SYSRQ_SERIAL
+       bool "Enable magic SysRq key over serial"
+       depends on MAGIC_SYSRQ
+       default y
+       help
+         Many embedded boards have a disconnected TTL level serial which can
+         generate some garbage that can lead to spurious false sysrq detects.
+         This option allows you to decide whether you want to enable the
+         magic SysRq key.
+
 config DEBUG_KERNEL
        bool "Kernel debugging"
        help