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Subject[PATCH 2/2] - usbserial: race-condition fix.

Fixes open()/close() race-condition in the access of the port structure.

When the race happens, the port in use becomes invalid, and the user must try
to get the next free port (repluging the device, for example).

Described in more detail in this thread:

http://marc.theaimsgroup.com/?l=linux-kernel&m=113216151918308&w=2

Signed-off-by: Luiz Capitulino <lcapitulino@mandriva.com.br>

drivers/usb/serial/usb-serial.c | 14 +++++++++++++-
drivers/usb/serial/usb-serial.h | 2 ++
2 files changed, 15 insertions(+), 1 deletion(-)
diff -Nparu -X /home/lcapitulino/kernels/dontdiff a/drivers/usb/serial/usb-serial.c a~/drivers/usb/serial/usb-serial.c
--- a/drivers/usb/serial/usb-serial.c 2005-11-22 10:50:33.000000000 -0200
+++ a~/drivers/usb/serial/usb-serial.c 2005-11-22 11:31:46.000000000 -0200
@@ -30,6 +30,7 @@
#include <linux/list.h>
#include <linux/smp_lock.h>
#include <asm/uaccess.h>
+#include <asm/semaphore.h>
#include <linux/usb.h>
#include "usb-serial.h"
#include "pl2303.h"
@@ -190,6 +191,9 @@ static int serial_open (struct tty_struc
port = serial->port[portNumber];
if (!port)
return -ENODEV;
+
+ if (down_interruptible(&port->sem))
+ return -ERESTARTSYS;

++port->open_count;

@@ -215,6 +219,7 @@ static int serial_open (struct tty_struc
goto bailout_module_put;
}

+ up(&port->sem);
return 0;

bailout_module_put:
@@ -222,6 +227,7 @@ bailout_module_put:
bailout_kref_put:
kref_put(&serial->kref, destroy_serial);
port->open_count = 0;
+ up(&port->sem);
return retval;
}

@@ -234,8 +240,10 @@ static void serial_close(struct tty_stru

dbg("%s - port %d", __FUNCTION__, port->number);

+ down(&port->sem);
+
if (port->open_count == 0)
- return;
+ goto out;

--port->open_count;
if (port->open_count == 0) {
@@ -253,6 +261,9 @@ static void serial_close(struct tty_stru
}

kref_put(&port->serial->kref, destroy_serial);
+
+out:
+ up(&port->sem);
}

static int serial_write (struct tty_struct * tty, const unsigned char *buf, int count)
@@ -774,6 +785,7 @@ int usb_serial_probe(struct usb_interfac
port->number = i + serial->minor;
port->serial = serial;
spin_lock_init(&port->lock);
+ sema_init(&port->sem, 1);
INIT_WORK(&port->work, usb_serial_port_softint, port);
serial->port[i] = port;
}
diff -Nparu -X /home/lcapitulino/kernels/dontdiff a/drivers/usb/serial/usb-serial.h a~/drivers/usb/serial/usb-serial.h
--- a/drivers/usb/serial/usb-serial.h 2005-11-22 10:50:42.000000000 -0200
+++ a~/drivers/usb/serial/usb-serial.h 2005-11-22 11:31:46.000000000 -0200
@@ -16,6 +16,7 @@

#include <linux/config.h>
#include <linux/kref.h>
+#include <asm/semaphore.h>

#define SERIAL_TTY_MAJOR 188 /* Nice legal number now */
#define SERIAL_TTY_MINORS 255 /* loads of devices :) */
@@ -60,6 +61,7 @@ struct usb_serial_port {
struct usb_serial * serial;
struct tty_struct * tty;
spinlock_t lock;
+ struct semaphore sem;
unsigned char number;

unsigned char * interrupt_in_buffer;

--
Luiz Fernando N. Capitulino
-
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