Hi,
there's a problem with linux/drivers/char/serial.c that appears when using
the LIRC serial port drivers (see http://www.lirc.org). Here's how to
reproduce the problem:
1. Load the lirc_serial module (included in the LIRC package). This module
uses request_region() for the used serial port's IO space.
2. Load the kernel serial module. In rs_init() the available serial ports
are initialized. For the port already claimed by the lirc_serial module
check_region() fails and state->type for this port stays PORT_UNKNOWN.
Now the problem:
3. Open the /dev/ttySx for the port that is occupied by the lirc_serial
module. rs_open() does not check the state of the serial port and returns
no error. Now you can use setserial to hijack the port... lirc_serial
stops working.
The patch below fixes the problem for me (tested with 2.2.19 and 2.2.20).
There's one problem with this patch though. Once state->type ist
PORT_UNKNOWN for a port there's no way to reclaim the port with e.g.
setserial unless you remove the serial port module and load it again.
Christoph
PS: I'm not subscribed, cc me if replying.
--- Schnipp ---
--- linux/drivers/char/serial.c Sun Mar 25 18:37:31 2001
+++ serial.c Tue Jan 15 18:20:59 2002
@@ -928,6 +928,11 @@
unsigned short ICP;
#endif
+ if(state->type == PORT_UNKNOWN)
+ {
+ return -ENODEV;
+ }
+
page = get_free_page(GFP_KERNEL);
if (!page)
return -ENOMEM;
@@ -1738,7 +1743,10 @@
info->xmit_fifo_size = state->xmit_fifo_size =
new_serial.xmit_fifo_size;
- release_region(state->port,8);
+ if(old_state.type != PORT_UNKNOWN)
+ {
+ release_region(state->port,8);
+ }
if (change_port || change_irq) {
/*
* We need to shutdown the serial port at the old
@@ -1750,8 +1758,14 @@
info->hub6 = state->hub6 = new_serial.hub6;
}
if (state->type != PORT_UNKNOWN)
+ {
+ retval=check_region(state->port,8);
+ if(retval<0)
+ {
+ return retval;
+ }
request_region(state->port,8,"serial(set)");
-
+ }
check_and_exit:
if (!state->port || !state->type)
@@ -3586,3 +3600,4 @@
return kmem_start;
}
#endif
+
--- Schnipp ---
On Sat, Feb 02, 2002 at 11:21:00PM +0000, Christoph Bartelmus wrote:
> Now the problem:
> 3. Open the /dev/ttySx for the port that is occupied by the lirc_serial
> module. rs_open() does not check the state of the serial port and returns
> no error. Now you can use setserial to hijack the port... lirc_serial
> stops working.
One of setserial's basic functions is to configure a ttyS device for a
serial port that you know is there. In this patch, you are preventing
any port that is in 'PORT_UNKNOWN' state from being changed, even if
you want to change the IRQ and IO base address. This is a different,
but nevertheless fundamental problem.
The real bug is that serial.c should allows you to change the port from
'PORT_UNKNOWN' even when it can't grab the resources for the port.
Thanks for finding it - are you able to work on this more to come up
with a better fix?
--
Russell King ([email protected]) The developer of ARM Linux
http://www.arm.linux.org.uk/personal/aboutme.html