Re: tty_register_device NULL pointer dereference in 2.6.31-rc4

Dave Young
2009-08-01T03:17:05Z

On Fri, Jul 31, 2009 at 01:20:19PM +0200, Oliver Hartkopp wrote:
> Dave Young wrote:
> > On Fri, Jul 31, 2009 at 5:39 PM, Dave Young<hidave.darkstar@gmail.com> wrote:
> >> On Thu, Jul 30, 2009 at 12:05:55PM +0200, Oliver Hartkopp wrote:
> >>> Dave Young wrote:
> >>>> On Wed, Jul 29, 2009 at 10:00 PM, Oliver Hartkopp<oliver@hartkopp.net> wrote:
> >>>>> Hi Dave,
> >>>>>
> >>>>> i got it again - even with your patch (that's why it's 2.6.31-rc4-dirty in the
> >>>>> attached screenshot).
> >>>> Weird, the oops occurs between sock init and tty init routines. Could
> >>>> you tell your bluez version and your configuration?
> >>>>
> >>> No problem:
> >> Thanks.
> >>
> >> It's still reasonable, after rfcomm sock layer initialized, userspace do sock ioctl callback but tty layer was not initilized yet at this time.
> >>
> >> Could you confirm it by applying following debug patch on top of my previous patch? if you get more oops with it then above reason will be right.
> >>
> >> --- linux-2.6.orig/net/bluetooth/rfcomm/core.c 2009-07-31 17:14:07.000000000 +0800
> >> +++ linux-2.6/net/bluetooth/rfcomm/core.c 2009-07-31 17:30:39.000000000 +0800
> >> @@ -36,6 +36,7 @@
> >> #include <linux/net.h>
> >> #include <linux/mutex.h>
> >> #include <linux/kthread.h>
> >> +#include <linux/nmi.h>
> >>
> >> #include <net/sock.h>
> >> #include <asm/uaccess.h>
> >> @@ -2080,7 +2081,7 @@ static CLASS_ATTR(rfcomm_dlc, S_IRUGO, r
> >> /* ---- Initialization ---- */
> >> static int __init rfcomm_init(void)
> >> {
> >> - int ret;
> >> + int ret, i;
> >>
> >> l2cap_load();
> >>
> >> @@ -2088,6 +2089,12 @@ static int __init rfcomm_init(void)
> >> if (ret)
> >> goto out_sock;
> >>
> >> + /* delay 5 seconds to trigger the tty bug */
> >> + for (i = 0; i < 50; i++) {
> >> + touch_nmi_watchdog();
> >> + mdelay(100);
> >
> > Hi, for this case, msleep is better, you can just replace the above
> > two lines with msleep(100)
> >
>
> Hi Dave,
>
> applied this patch and replaced mdelay(100) with msleep(100).
>
> I got two crashes and three proper boots.
>
> The crashes look like the formerly posted screenshots.
> When it boots properly i can see the delay in the boot process.
>
> Does this help?

Yes, I think so.

Please unapply the before two patch, try the following v2 patch instead.
Changes from v1: fixes 'goto' path again, make tty init before sock init.

Thanks.
---

rfcomm tty may be used before rfcomm_tty_driver initilized,
The problem is that now socket layer init before tty layer, if userspace
program do socket callback right here then oops will happen.

reporting in:
http://marc.info/?l=linux-bluetooth&m=124404919324542&w=2

make 3 changes:
1. remove #ifdef in rfcomm/core.c,
make it blank function when rfcomm tty not selected in rfcomm.h

2. tune the rfcomm_init error patch to ensure
tty driver initilized before rfcomm socket usage.

3. remove __exit for rfcomm_cleanup_sockets
because above change need call it in a __init function.

CC: Alan Cox <alan@lxorguk.ukuu.org.uk>
Reported-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
--
include/net/bluetooth/rfcomm.h | 13 ++++++++++++-
net/bluetooth/rfcomm/core.c | 29 ++++++++++++++++++++---------
net/bluetooth/rfcomm/sock.c | 2 +-
3 files changed, 33 insertions(+), 11 deletions(-)

--- linux-2.6.orig/include/net/bluetooth/rfcomm.h 2009-08-01 10:53:18.000000000 +0800
+++ linux-2.6/include/net/bluetooth/rfcomm.h 2009-08-01 10:55:29.000000000 +0800
@@ -355,7 +355,18 @@ struct rfcomm_dev_list_req {
};

int rfcomm_dev_ioctl(struct sock *sk, unsigned int cmd, void __user *arg);
+
+#ifdef CONFIG_BT_RFCOMM_TTY
int rfcomm_init_ttys(void);
void rfcomm_cleanup_ttys(void);
-
+#else
+static inline int rfcomm_init_ttys(void)
+{
+ return 0;
+}
+static inline int rfcomm_cleanup_ttys(void)
+{
+ return 0;
+}
+#endif
#endif /* __RFCOMM_H */
--- linux-2.6.orig/net/bluetooth/rfcomm/core.c 2009-08-01 10:53:18.000000000 +0800
+++ linux-2.6/net/bluetooth/rfcomm/core.c 2009-08-01 11:03:24.000000000 +0800
@@ -2080,28 +2080,41 @@ static CLASS_ATTR(rfcomm_dlc, S_IRUGO, r
/* ---- Initialization ---- */
static int __init rfcomm_init(void)
{
+ int ret;
+
l2cap_load();

hci_register_cb(&rfcomm_cb);

rfcomm_thread = kthread_run(rfcomm_run, NULL, "krfcommd");
if (IS_ERR(rfcomm_thread)) {
- hci_unregister_cb(&rfcomm_cb);
- return PTR_ERR(rfcomm_thread);
+ ret = PTR_ERR(rfcomm_thread);
+ goto out_thread;
}

if (class_create_file(bt_class, &class_attr_rfcomm_dlc) < 0)
BT_ERR("Failed to create RFCOMM info file");

- rfcomm_init_sockets();
-
-#ifdef CONFIG_BT_RFCOMM_TTY
- rfcomm_init_ttys();
-#endif
+ ret = rfcomm_init_ttys();
+ if (ret)
+ goto out_tty;
+
+ ret = rfcomm_init_sockets();
+ if (ret)
+ goto out_sock;

BT_INFO("RFCOMM ver %s", VERSION);

return 0;
+
+out_sock:
+ rfcomm_cleanup_ttys();
+out_tty:
+ kthread_stop(rfcomm_thread);
+out_thread:
+ hci_unregister_cb(&rfcomm_cb);
+
+ return ret;
}

static void __exit rfcomm_exit(void)
@@ -2112,9 +2125,7 @@ static void __exit rfcomm_exit(void)

kthread_stop(rfcomm_thread);

-#ifdef CONFIG_BT_RFCOMM_TTY
rfcomm_cleanup_ttys();
-#endif

rfcomm_cleanup_sockets();
}
--- linux-2.6.orig/net/bluetooth/rfcomm/sock.c 2009-08-01 10:53:18.000000000 +0800
+++ linux-2.6/net/bluetooth/rfcomm/sock.c 2009-08-01 10:55:29.000000000 +0800
@@ -1132,7 +1132,7 @@ error:
return err;
}

-void __exit rfcomm_cleanup_sockets(void)
+void rfcomm_cleanup_sockets(void)
{
class_remove_file(bt_class, &class_attr_rfcomm);