Messages in this thread Patch in this message | | | Date | Wed, 23 Nov 2005 17:02:45 -0200 | From | Luiz Fernando Capitulino <> | Subject | Re: [RESEND 2/2] - usbserial: race-condition fix. |
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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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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