[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
--- 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 @@
port = serial->port[portNumber];
if (!port)
return -ENODEV;
+
+ if (down_interruptible(&port->sem))
+ return -ERESTARTSYS;
++port->open_count;
@@ -215,6 +219,7 @@
goto bailout_module_put;
}
+ up(&port->sem);
return 0;
bailout_module_put:
@@ -222,6 +227,7 @@
bailout_kref_put:
kref_put(&serial->kref, destroy_serial);
port->open_count = 0;
+ up(&port->sem);
return retval;
}
@@ -234,8 +240,10 @@
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 @@
}
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 @@
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
--- 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 * serial;
struct tty_struct * tty;
spinlock_t lock;
+ struct semaphore sem;
unsigned char number;
unsigned char * interrupt_in_buffer;