[PATCH] binder: fix UAF of ref->proc caused by race condition

[PATCH] binder: fix UAF of ref->proc caused by race condition

[Carlos Llamas]

A transaction of type BINDER_TYPE_WEAK_HANDLE can fail to increment the
reference for a node. In this case, the target proc normally releases
the failed reference upon close as expected. However, if the target is
dying in parallel the call will race with binder_deferred_release(), so
the target could have released all of its references by now leaving the
cleanup of the new failed reference unhandled.

The transaction then ends and the target proc gets released making the
ref->proc now a dangling pointer. Later on, ref->node is closed and we
attempt to take spin_lock(&ref->proc->inner_lock), which leads to the
use-after-free bug reported below. Let's fix this by cleaning up the
failed reference on the spot instead of relying on the target to do so.

  ==================================================================
  BUG: KASAN: use-after-free in _raw_spin_lock+0xa8/0x150
  Write of size 4 at addr ffff5ca207094238 by task kworker/1:0/590

  CPU: 1 PID: 590 Comm: kworker/1:0 Not tainted 5.19.0-rc8 #10
  Hardware name: linux,dummy-virt (DT)
  Workqueue: events binder_deferred_func
  Call trace:
   dump_backtrace.part.0+0x1d0/0x1e0
   show_stack+0x18/0x70
   dump_stack_lvl+0x68/0x84
   print_report+0x2e4/0x61c
   kasan_report+0xa4/0x110
   kasan_check_range+0xfc/0x1a4
   __kasan_check_write+0x3c/0x50
   _raw_spin_lock+0xa8/0x150
   binder_deferred_func+0x5e0/0x9b0
   process_one_work+0x38c/0x5f0
   worker_thread+0x9c/0x694
   kthread+0x188/0x190
   ret_from_fork+0x10/0x20

Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
 drivers/android/binder.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 362c0deb65f1..9d42afe60180 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1361,6 +1361,18 @@ static int binder_inc_ref_for_node(struct binder_proc *proc,
 	}
 	ret = binder_inc_ref_olocked(ref, strong, target_list);
 	*rdata = ref->data;
+	if (ret && ref == new_ref) {
+		/*
+		 * Cleanup the failed reference here as the target
+		 * could now be dead and have already released its
+		 * references by now. Calling on the new reference
+		 * with strong=0 and a tmp_refs will not decrement
+		 * the node. The new_ref gets kfree'd below.
+		 */
+		binder_cleanup_ref_olocked(new_ref);
+		ref = NULL;
+	}
+
 	binder_proc_unlock(proc);
 	if (new_ref && ref != new_ref)
 		/*
-- 
2.37.1.455.g008518b4e5-goog

Re: [PATCH] binder: fix UAF of ref->proc caused by race condition

[Christian Brauner]

On Mon, Aug 01, 2022 at 06:25:11PM +0000, Carlos Llamas wrote:
> A transaction of type BINDER_TYPE_WEAK_HANDLE can fail to increment the
> reference for a node. In this case, the target proc normally releases
> the failed reference upon close as expected. However, if the target is
> dying in parallel the call will race with binder_deferred_release(), so
> the target could have released all of its references by now leaving the
> cleanup of the new failed reference unhandled.
> 
> The transaction then ends and the target proc gets released making the
> ref->proc now a dangling pointer. Later on, ref->node is closed and we
> attempt to take spin_lock(&ref->proc->inner_lock), which leads to the
> use-after-free bug reported below. Let's fix this by cleaning up the
> failed reference on the spot instead of relying on the target to do so.
> 
>   ==================================================================
>   BUG: KASAN: use-after-free in _raw_spin_lock+0xa8/0x150
>   Write of size 4 at addr ffff5ca207094238 by task kworker/1:0/590
> 
>   CPU: 1 PID: 590 Comm: kworker/1:0 Not tainted 5.19.0-rc8 #10
>   Hardware name: linux,dummy-virt (DT)
>   Workqueue: events binder_deferred_func
>   Call trace:
>    dump_backtrace.part.0+0x1d0/0x1e0
>    show_stack+0x18/0x70
>    dump_stack_lvl+0x68/0x84
>    print_report+0x2e4/0x61c
>    kasan_report+0xa4/0x110
>    kasan_check_range+0xfc/0x1a4
>    __kasan_check_write+0x3c/0x50
>    _raw_spin_lock+0xa8/0x150
>    binder_deferred_func+0x5e0/0x9b0
>    process_one_work+0x38c/0x5f0
>    worker_thread+0x9c/0x694
>    kthread+0x188/0x190
>    ret_from_fork+0x10/0x20
> 
> Signed-off-by: Carlos Llamas <cmllamas@google.com>
> ---

Seems sane,
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>

Re: [PATCH] binder: fix UAF of ref->proc caused by race condition

[Carlos Llamas]

On Mon, Aug 01, 2022 at 06:25:11PM +0000, Carlos Llamas wrote:
> A transaction of type BINDER_TYPE_WEAK_HANDLE can fail to increment the
> reference for a node. In this case, the target proc normally releases
> the failed reference upon close as expected. However, if the target is
> dying in parallel the call will race with binder_deferred_release(), so
> the target could have released all of its references by now leaving the
> cleanup of the new failed reference unhandled.
> 
> The transaction then ends and the target proc gets released making the
> ref->proc now a dangling pointer. Later on, ref->node is closed and we
> attempt to take spin_lock(&ref->proc->inner_lock), which leads to the
> use-after-free bug reported below. Let's fix this by cleaning up the
> failed reference on the spot instead of relying on the target to do so.
> 
>   ==================================================================
>   BUG: KASAN: use-after-free in _raw_spin_lock+0xa8/0x150
>   Write of size 4 at addr ffff5ca207094238 by task kworker/1:0/590
> 
>   CPU: 1 PID: 590 Comm: kworker/1:0 Not tainted 5.19.0-rc8 #10
>   Hardware name: linux,dummy-virt (DT)
>   Workqueue: events binder_deferred_func
>   Call trace:
>    dump_backtrace.part.0+0x1d0/0x1e0
>    show_stack+0x18/0x70
>    dump_stack_lvl+0x68/0x84
>    print_report+0x2e4/0x61c
>    kasan_report+0xa4/0x110
>    kasan_check_range+0xfc/0x1a4
>    __kasan_check_write+0x3c/0x50
>    _raw_spin_lock+0xa8/0x150
>    binder_deferred_func+0x5e0/0x9b0
>    process_one_work+0x38c/0x5f0
>    worker_thread+0x9c/0x694
>    kthread+0x188/0x190
>    ret_from_fork+0x10/0x20
> 
> Signed-off-by: Carlos Llamas <cmllamas@google.com>
> ---
>  drivers/android/binder.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 362c0deb65f1..9d42afe60180 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1361,6 +1361,18 @@ static int binder_inc_ref_for_node(struct binder_proc *proc,
>  	}
>  	ret = binder_inc_ref_olocked(ref, strong, target_list);
>  	*rdata = ref->data;
> +	if (ret && ref == new_ref) {
> +		/*
> +		 * Cleanup the failed reference here as the target
> +		 * could now be dead and have already released its
> +		 * references by now. Calling on the new reference
> +		 * with strong=0 and a tmp_refs will not decrement
> +		 * the node. The new_ref gets kfree'd below.
> +		 */
> +		binder_cleanup_ref_olocked(new_ref);
> +		ref = NULL;
> +	}
> +
>  	binder_proc_unlock(proc);
>  	if (new_ref && ref != new_ref)
>  		/*
> -- 
> 2.37.1.455.g008518b4e5-goog
> 

Sorry, I forgot to CC stable. This patch should be applied to all stable
kernels starting with 4.14 and higher.

Cc: stable@vger.kernel.org # 4.14+

Re: [PATCH] binder: fix UAF of ref->proc caused by race condition

[Greg Kroah-Hartman]

On Tue, Aug 02, 2022 at 07:40:32PM +0000, Carlos Llamas wrote:
> On Mon, Aug 01, 2022 at 06:25:11PM +0000, Carlos Llamas wrote:
> > A transaction of type BINDER_TYPE_WEAK_HANDLE can fail to increment the
> > reference for a node. In this case, the target proc normally releases
> > the failed reference upon close as expected. However, if the target is
> > dying in parallel the call will race with binder_deferred_release(), so
> > the target could have released all of its references by now leaving the
> > cleanup of the new failed reference unhandled.
> > 
> > The transaction then ends and the target proc gets released making the
> > ref->proc now a dangling pointer. Later on, ref->node is closed and we
> > attempt to take spin_lock(&ref->proc->inner_lock), which leads to the
> > use-after-free bug reported below. Let's fix this by cleaning up the
> > failed reference on the spot instead of relying on the target to do so.
> > 
> >   ==================================================================
> >   BUG: KASAN: use-after-free in _raw_spin_lock+0xa8/0x150
> >   Write of size 4 at addr ffff5ca207094238 by task kworker/1:0/590
> > 
> >   CPU: 1 PID: 590 Comm: kworker/1:0 Not tainted 5.19.0-rc8 #10
> >   Hardware name: linux,dummy-virt (DT)
> >   Workqueue: events binder_deferred_func
> >   Call trace:
> >    dump_backtrace.part.0+0x1d0/0x1e0
> >    show_stack+0x18/0x70
> >    dump_stack_lvl+0x68/0x84
> >    print_report+0x2e4/0x61c
> >    kasan_report+0xa4/0x110
> >    kasan_check_range+0xfc/0x1a4
> >    __kasan_check_write+0x3c/0x50
> >    _raw_spin_lock+0xa8/0x150
> >    binder_deferred_func+0x5e0/0x9b0
> >    process_one_work+0x38c/0x5f0
> >    worker_thread+0x9c/0x694
> >    kthread+0x188/0x190
> >    ret_from_fork+0x10/0x20
> > 
> > Signed-off-by: Carlos Llamas <cmllamas@google.com>
> > ---
> >  drivers/android/binder.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index 362c0deb65f1..9d42afe60180 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -1361,6 +1361,18 @@ static int binder_inc_ref_for_node(struct binder_proc *proc,
> >  	}
> >  	ret = binder_inc_ref_olocked(ref, strong, target_list);
> >  	*rdata = ref->data;
> > +	if (ret && ref == new_ref) {
> > +		/*
> > +		 * Cleanup the failed reference here as the target
> > +		 * could now be dead and have already released its
> > +		 * references by now. Calling on the new reference
> > +		 * with strong=0 and a tmp_refs will not decrement
> > +		 * the node. The new_ref gets kfree'd below.
> > +		 */
> > +		binder_cleanup_ref_olocked(new_ref);
> > +		ref = NULL;
> > +	}
> > +
> >  	binder_proc_unlock(proc);
> >  	if (new_ref && ref != new_ref)
> >  		/*
> > -- 
> > 2.37.1.455.g008518b4e5-goog
> > 
> 
> Sorry, I forgot to CC stable. This patch should be applied to all stable
> kernels starting with 4.14 and higher.
> 
> Cc: stable@vger.kernel.org # 4.14+

Thanks, I'll add this when I queue it up after 5.20-rc1 is out.

greg k-h

Re: [PATCH] binder: fix UAF of ref->proc caused by race condition

[Carlos Llamas]

On Wed, Aug 03, 2022 at 09:29:24AM +0200, Greg Kroah-Hartman wrote:
> 
> Thanks, I'll add this when I queue it up after 5.20-rc1 is out.
> 
> greg k-h

Hi Greg,

I think this might have fallen through the cracks, I can't find it in
char-misc or linux-next trees.

--
Carlos Llamas

Re: [PATCH] binder: fix UAF of ref->proc caused by race condition

[Greg Kroah-Hartman]

On Wed, Aug 17, 2022 at 10:04:50PM +0000, Carlos Llamas wrote:
> On Wed, Aug 03, 2022 at 09:29:24AM +0200, Greg Kroah-Hartman wrote:
> > 
> > Thanks, I'll add this when I queue it up after 5.20-rc1 is out.
> > 
> > greg k-h
> 
> Hi Greg,
> 
> I think this might have fallen through the cracks, I can't find it in
> char-misc or linux-next trees.

-rc1 only came out a few days ago, and I have a lot to catch up on:
	$ mdfrm -c ~/mail/todo/
	1770 messages in /home/gregkh/mail/todo/

Please give me a chance...

thanks,

greg k-h

Re: [PATCH] binder: fix UAF of ref->proc caused by race condition

[Carlos Llamas]

On Thu, Aug 18, 2022 at 07:26:01AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Aug 17, 2022 at 10:04:50PM +0000, Carlos Llamas wrote:
> > On Wed, Aug 03, 2022 at 09:29:24AM +0200, Greg Kroah-Hartman wrote:
> > > 
> > > Thanks, I'll add this when I queue it up after 5.20-rc1 is out.
> > > 
> > > greg k-h
> > 
> > Hi Greg,
> > 
> > I think this might have fallen through the cracks, I can't find it in
> > char-misc or linux-next trees.
> 
> -rc1 only came out a few days ago, and I have a lot to catch up on:
> 	$ mdfrm -c ~/mail/todo/
> 	1770 messages in /home/gregkh/mail/todo/
> 
> Please give me a chance...
> 
> thanks,
> 
> greg k-h

Oh my bad, I got mixed up with 5.20-rc1 and 6.0-rc1. Please disregard my
previous email.