Received-SPF: pass (google.com: domain of linux-kernel+bounces-126816-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Precedence: bulk
MIME-Version: 1.0
References: <20240330190115.1877819-1-cmllamas@google.com>
In-Reply-To: <20240330190115.1877819-1-cmllamas@google.com>
From: Todd Kjos <tkjos@google.com>
Date: Mon, 1 Apr 2024 08:38:20 -0700
Message-ID: <CAHRSSExq7UkD1D4Q632hf0a6f=jB1O2zhUrrgY6tudtxnynU5g@mail.gmail.com>
Subject: Re: [PATCH] binder: check offset alignment in binder_get_object()
To: Carlos Llamas <cmllamas@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>, 
	Todd Kjos <tkjos@android.com>, Martijn Coenen <maco@android.com>, 
	Joel Fernandes <joel@joelfernandes.org>, Christian Brauner <brauner@kernel.org>, 
	Suren Baghdasaryan <surenb@google.com>, linux-kernel@vger.kernel.org, kernel-team@android.com, 
	Alice Ryhl <aliceryhl@google.com>, stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Sat, Mar 30, 2024 at 12:01=E2=80=AFPM Carlos Llamas <cmllamas@google.com=
> wrote:
>
> Commit 6d98eb95b450 ("binder: avoid potential data leakage when copying
> txn") introduced changes to how binder objects are copied. In doing so,
> it unintentionally removed an offset alignment check done through calls
> to binder_alloc_copy_from_buffer() -> check_buffer().
>
> These calls were replaced in binder_get_object() with copy_from_user(),
> so now an explicit offset alignment check is needed here. This avoids
> later complications when unwinding the objects gets harder.
>
> It is worth noting this check existed prior to commit 7a67a39320df
> ("binder: add function to copy binder object from buffer"), likely
> removed due to redundancy at the time.
>
> Fixes: 6d98eb95b450 ("binder: avoid potential data leakage when copying t=
xn")
> Cc: stable@vger.kernel.org
> Signed-off-by: Carlos Llamas <cmllamas@google.com>

Acked-by: Todd Kjos <tkjos@google.com>

> ---
>  drivers/android/binder.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index bad28cf42010..dd6923d37931 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1708,8 +1708,10 @@ static size_t binder_get_object(struct binder_proc=
 *proc,
>         size_t object_size =3D 0;
>
>         read_size =3D min_t(size_t, sizeof(*object), buffer->data_size - =
offset);
> -       if (offset > buffer->data_size || read_size < sizeof(*hdr))
> +       if (offset > buffer->data_size || read_size < sizeof(*hdr) ||
> +           !IS_ALIGNED(offset, sizeof(u32)))
>                 return 0;
> +
>         if (u) {
>                 if (copy_from_user(object, u + offset, read_size))
>                         return 0;
> --
> 2.44.0.478.gd926399ef9-goog
>