[PATCH] USB: usbserial: race-condition fix.

There is a race-condition in usb-serial driver that can be triggered if
a processes does 'port->tty->driver_data = NULL' in serial_close() while
other processes is in kernel-space about to call serial_ioctl() on the
same port.

This happens because a process can open the device while there is
another one closing it.

The patch below fixes that by adding a semaphore to ensure that no
process will open the device while another process is closing it.

Note that we can't use spinlocks here, since serial_open() and
serial_close() can sleep.

Signed-off-by: Luiz Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 5bc023c..8bc8337 100644 (file)
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -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_struct *tty, struct file * filp)
        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_struct *tty, struct file * filp)
                        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_struct *tty, struct file * filp)
 
        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_struct *tty, struct file * filp)
        }
 
        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_interface *interface,
                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 --git a/drivers/usb/serial/usb-serial.h b/drivers/usb/serial/usb-serial.h
index 238a5a8..d7d27c3 100644 (file)
--- a/drivers/usb/serial/usb-serial.h
+++ b/drivers/usb/serial/usb-serial.h
@@ -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 :) */
@@ -30,6 +31,8 @@
  * @serial: pointer back to the struct usb_serial owner of this port.
  * @tty: pointer to the corresponding tty for this port.
  * @lock: spinlock to grab when updating portions of this structure.
+ * @sem: semaphore used to synchronize serial_open() and serial_close()
+ *     access for this port.
  * @number: the number of the port (the minor number).
  * @interrupt_in_buffer: pointer to the interrupt in buffer for this port.
  * @interrupt_in_urb: pointer to the interrupt in struct urb for this port.
@@ -60,6 +63,7 @@ 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;