Commit 8a4613f0 authored by Luiz Fernando Capitulino's avatar Luiz Fernando Capitulino Committed by Greg Kroah-Hartman
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[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: default avatarLuiz Capitulino <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 487f9c67
......@@ -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))
......@@ -215,6 +219,7 @@ static int serial_open (struct tty_struct *tty, struct file * filp)
goto bailout_module_put;
return 0;
......@@ -222,6 +227,7 @@ bailout_module_put:
kref_put(&serial->kref, destroy_serial);
port->open_count = 0;
return retval;
......@@ -234,8 +240,10 @@ static void serial_close(struct tty_struct *tty, struct file * filp)
dbg("%s - port %d", __FUNCTION__, port->number);
if (port->open_count == 0)
goto out;
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);
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;
sema_init(&port->sem, 1);
INIT_WORK(&port->work, usb_serial_port_softint, port);
serial->port[i] = port;
......@@ -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;
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