Re: [RESEND 2/2] - usbserial: race-condition fix.

[Luiz Fernando Capitulino <lcapitulino@mandriva.com.br>]

On Wed, 23 Nov 2005 10:01:08 -0800
Greg KH <gregkh@suse.de> wrote:

| On Wed, Nov 23, 2005 at 03:46:50PM -0200, Luiz Fernando Capitulino wrote:
| > 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.
| 
| How will you clean it up?

 Replacing the 'write_urb_busy' member type to atomic_t (and using the
atomic functions, of course), since the current spinlock seems to be only
used to have atomic access to 'write_urb_busy'.

 Thanks to Eduardo for noting this.

| >  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
| 
| Please put the full detail in the email, so I can put it in the
| ChangeLog so people have an easy place to get the proper information.
| 
| Care to redo it again?

 No. But hope the CC'd people doesn't too. :)

 Here goes:


 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>

 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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