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Subject[RESEND 2/2] - usbserial: race-condition fix.
On Tue, 22 Nov 2005 14:13:53 -0800
Greg KH <gregkh@suse.de> wrote:

| On Tue, Nov 22, 2005 at 07:59:26PM -0200, Luiz Fernando Capitulino wrote:
| > @@ -60,6 +61,7 @@ struct usb_serial_port {
| > struct usb_serial * serial;
| > struct tty_struct * tty;
| > spinlock_t lock;
| > + struct semaphore sem;
|
| You forgot to document what this semaphore is used for.

Here goes the second patch again, with the documentation now.

As I said before, would be good to apply these two patches now, and I
can cleanup the spinlock usage until next week.


Fixes a race-condition in the access of the port structure, described
in detail at: 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 | 4 ++++
2 files changed, 17 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 2005-11-23 15:30:20.000000000 -0200
+++ a~/drivers/usb/serial/usb-serial.c 2005-11-23 15:23:19.000000000 -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 2005-11-23 15:30:20.000000000 -0200
+++ a~/drivers/usb/serial/usb-serial.h 2005-11-23 15:23:59.000000000 -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 :) */
@@ -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;

--
Luiz Fernando N. Capitulino
-
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