Re: Oops/Warning report for the week of March 28th 2008

Linus Torvalds
2008-03-28T20:52:09Z

On Fri, 28 Mar 2008, Linus Torvalds wrote:
>
> Is there something obvious that I'm missing? I'd really like to see the
> whole posting that the oops came from. Do you save the originals or even
> just message ID's from the ones you pick from emails?

Hmm. Definitely not from the kernel mailing list. I'm intrigued, where did
that oops #5814 come from (picked a recent one at random)?

The thing is recent, and oopses on "mutex_lock(dev->mutex)" in
input_release_device. In particular, the path *seems* to be this one:

evdev_release ->
evdev_ungrab ->
input_release_device ->
mutex_lock ->
mutex_lock_nested ->
__mutex_lock_common ->
list_add_tail(&waiter.list, &lock->wait_list)

where "lock->wait_list.prev" seems to be 0x6b6b6b6b6b6b6b6b, which is the
use-after-free poison pattern.

(In fact, I think the access that actually oopses is when the
debug version of __list_add() does

if (unlikely(prev->next != next)) {

because that "prev" pointer is crap).

So it seems that when input_release_device() does:

struct input_dev *dev = handle->dev;

mutex_lock(&dev->mutex);

the "dev" it uses has already been released. And this only shows up as a
problem when you have slab debugging turned on (like the Fedora kernels
do, thank you all Fedora guys).

The odd thing is that I don't think any of this code has really changed
recently.

Linus