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[34.127.76.238]) by smtp.gmail.com with ESMTPSA id w23-20020a1709027b9700b0016d1d1c376fsm53231pll.287.2022.08.02.12.40.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Aug 2022 12:40:35 -0700 (PDT) Date: Tue, 2 Aug 2022 19:40:32 +0000 From: Carlos Llamas To: Greg Kroah-Hartman , Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Todd Kjos , Martijn Coenen , Christian Brauner Cc: Joel Fernandes , Suren Baghdasaryan , kernel-team@android.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] binder: fix UAF of ref->proc caused by race condition Message-ID: References: <20220801182511.3371447-1-cmllamas@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220801182511.3371447-1-cmllamas@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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+