[PATCH 2/2] usb_serial: only allow sysrq on a console port

From: Jason Wessel
Date: Fri May 29 2009 - 14:35:15 EST

The only time a sysrq should get processed is if the attached device
is a console. This is intended to protect sysrq execution on a host
connected with a terminal program.

Here is the problem scenario:

host A <-- rs232 link --> host B

Host A is using mincom and a usb pl2303 device to connect to host b
which is a linux system with a usb pl2303 device acting as the serial
console. When host B is rebooted the pl2303 emits random junk
characters on reset. These character sequences contain serial break
signals most of the time and when translated to a sysrq have caused
host A to get random processes killed, reboots or power down.

It is true that in this setup with this patch host B might still have
the same problem as host A if you reboot host A. In most cases host A
is a development host which seldom gets rebooted, and you could turn
off sysrq temporarily on host B if you need to reboot host A.

Signed-off-by: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
drivers/usb/serial/generic.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index df56ed3..4797402 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -529,7 +529,7 @@ void usb_serial_generic_unthrottle(struct tty_struct *tty)

int usb_serial_handle_sysrq_char(struct usb_serial_port *port, unsigned int ch)
- if (port->sysrq) {
+ if (port->sysrq && port->console) {
if (ch && time_before(jiffies, port->sysrq)) {
handle_sysrq(ch, tty_port_tty_get(&port->port));
port->sysrq = 0;

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