linux-kernel - Re: [PATCH] binder: fix UAF in binder_netlink

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Message-ID: <aXHfYfNZ20-3J8qR@google.com>
Date: Thu, 22 Jan 2026 08:27:13 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Carlos Llamas <cmllamas@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Arve Hjønnevåg" <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, 
	Christian Brauner <brauner@...nel.org>, Li Li <dualli@...gle.com>, kernel-team@...roid.com, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] binder: fix UAF in binder_netlink_report()

On Wed, Jan 21, 2026 at 04:56:25PM +0000, Carlos Llamas wrote:
> On Wed, Jan 21, 2026 at 03:24:06PM +0000, Alice Ryhl wrote:
> > 
> > Erm, this solution seems dangerous to me. You access t->to_proc and
> > t->to_thread inside binder_netlink_report(), and if t has been freed,
> > could the same apply to t->to_proc or t->to_thread?
> > 
> > After looking a bit more: I can see now that you do call
> > 
> > 	if (target_thread)
> > 		binder_thread_dec_tmpref(target_thread);
> > 	binder_proc_dec_tmpref(target_proc);
> > 	if (target_node)
> > 		binder_dec_node_tmpref(target_node);
> > 
> > after this ... so I guess it can't go wrong in this particular way.
> 
> Right, the access to the target is safe because of the tmprefs just like
> the rest of the transaction().
> 
> > But I'm concerned that we will add fields in the future where this is
> > not the case. For example, let's say that tomorrow I want to include
> > t->buffer->clear_on_free in the printed data. If the transaction is
> > freed, then t->buffer might also be freed.
> 
> You actually can't access t->buffer already, there are scenarios where
> the t->buffer is released before calling binder_netlink_report().

Hmm, I suppose you are right. It may be worth mentioning that you can't
access t->buffer in a comment inside netlink_report?

Alice