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SubjectRe: [patch take 2] Re: linux-2.6.today: rtc_cmos init oops/panic in rtc_sysfs_remove_device()
On Thu, 01 Mar 2007 09:55:06 +0100
Mike Galbraith <efault@gmx.de> wrote:

> Dummy here created a use after free.
>
> Fix NULL pointer dereference in cmos_rtc registration failure path.
> Since we're freeing rtc in rtc_device_release(), there should be no need
> to NULL rtc->ops. Anybody who has a reference to the freed rtc after
> device release, and uses it, will hopefully explode violently.
>
> Signed-off-by: Mike Galbraith <efault@gmx.de>
>
> diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
> index 7a0d8ee..d338fb8 100644
> --- a/drivers/rtc/class.c
> +++ b/drivers/rtc/class.c
> @@ -113,9 +113,6 @@ EXPORT_SYMBOL_GPL(rtc_device_register);
> */
> void rtc_device_unregister(struct rtc_device *rtc)
> {
> - mutex_lock(&rtc->ops_lock);
> - rtc->ops = NULL;
> - mutex_unlock(&rtc->ops_lock);
> class_device_unregister(&rtc->class_dev);
> }
> EXPORT_SYMBOL_GPL(rtc_device_unregister);

Linus today merged the below, which I cunningly forgot to cc you on.

Can you please review current mainline, see if we still need fixes?

Thanks.


From: David Brownell <david-b@pacbell.net>

Fix an oops on the rtc_device_unregister() path by waiting until the last
moment before nulling the rtc->ops vector. Fix some potential oopses by
having the rtc_class_open()/rtc_class_close() interface increase the RTC's
reference count while an RTC handle is available outside the RTC framework.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
drivers/rtc/class.c | 14 ++++++++++----
drivers/rtc/interface.c | 3 ++-
2 files changed, 12 insertions(+), 5 deletions(-)
diff -puN drivers/rtc/class.c~rtc_cmos-oops-fix drivers/rtc/class.c
--- a/drivers/rtc/class.c~rtc_cmos-oops-fix
+++ a/drivers/rtc/class.c
@@ -113,10 +113,16 @@ EXPORT_SYMBOL_GPL(rtc_device_register);
*/
void rtc_device_unregister(struct rtc_device *rtc)
{
- mutex_lock(&rtc->ops_lock);
- rtc->ops = NULL;
- mutex_unlock(&rtc->ops_lock);
- class_device_unregister(&rtc->class_dev);
+ if (class_device_get(&rtc->class_dev) != NULL) {
+ mutex_lock(&rtc->ops_lock);
+ /* remove innards of this RTC, then disable it, before
+ * letting any rtc_class_open() users access it again
+ */
+ class_device_unregister(&rtc->class_dev);
+ rtc->ops = NULL;
+ mutex_unlock(&rtc->ops_lock);
+ class_device_put(&rtc->class_dev);
+ }
}
EXPORT_SYMBOL_GPL(rtc_device_unregister);

diff -puN drivers/rtc/interface.c~rtc_cmos-oops-fix drivers/rtc/interface.c
--- a/drivers/rtc/interface.c~rtc_cmos-oops-fix
+++ a/drivers/rtc/interface.c
@@ -179,7 +179,7 @@ struct class_device *rtc_class_open(char
down(&rtc_class->sem);
list_for_each_entry(class_dev_tmp, &rtc_class->children, node) {
if (strncmp(class_dev_tmp->class_id, name, BUS_ID_SIZE) == 0) {
- class_dev = class_dev_tmp;
+ class_dev = class_device_get(class_dev_tmp);
break;
}
}
@@ -197,6 +197,7 @@ EXPORT_SYMBOL_GPL(rtc_class_open);
void rtc_class_close(struct class_device *class_dev)
{
module_put(to_rtc_device(class_dev)->owner);
+ class_device_put(class_dev);
}
EXPORT_SYMBOL_GPL(rtc_class_close);

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