Re: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill_super

From: Dongliang Mu <mudongliangabcd@gmail.com>
To: Christian Brauner <brauner@kernel.org>
Cc: "Dongliang Mu" <dzm91@hust.edu.cn>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Todd Kjos" <tkjos@android.com>,
	"Martijn Coenen" <maco@android.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Carlos Llamas" <cmllamas@google.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Kees Cook" <keescook@chromium.org>,
	syzkaller <syzkaller@googlegroups.com>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill_super
Date: Mon, 15 Aug 2022 08:59:11 +0800	[thread overview]
Message-ID: <CAD-N9QW5qJw5NuA3GLwUuJavKccn7DY__NVDxRbazbjnAizR-Q@mail.gmail.com> (raw)
In-Reply-To: <20220812141849.nhwpvg6vte22lg2s@wittgenstein>

On Fri, Aug 12, 2022 at 10:18 PM Christian Brauner <brauner@kernel.org> wrote:
>
> On Fri, Aug 12, 2022 at 09:48:40PM +0800, Dongliang Mu wrote:
> > On Fri, Aug 12, 2022 at 9:41 PM Christian Brauner <brauner@kernel.org> wrote:
> > >
> > > On Fri, Aug 12, 2022 at 09:21:24PM +0800, Dongliang Mu wrote:
> > > > From: Dongliang Mu <mudongliangabcd@gmail.com>
> > > >
> > > > In binderfs_fill_super, if s_root is not successfully initialized by
> > > > d_make_root, the previous allocated s_sb_info will not be freed since
> > > > generic_shutdown_super first checks if sb->s_root and then does
> > > > put_super operation. The put_super operation calls binderfs_put_super
> > > > to deallocate s_sb_info and put ipc_ns. This will lead to memory leak
> > > > in binderfs_fill_super.
> > > >
> > > > Fix this by invoking binderfs_put_super at error sites before s_root
> > > > is successfully initialized.
> > > >
> > > > Fixes: 095cf502b31e ("binderfs: port to new mount api")
> > > > Reported-by: syzkaller <syzkaller@googlegroups.com>
> > > > Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
> > > > ---
> > >
> > > Seems right but where's the full syzbot link to the issue?
> > > Also, wouldn't (untested) sm like the below be better?:
> >
> > I originally would like to change the order to object initialization,
> > but I am not sure if they can be exchanged since many *_fill_super are
> > ended with d_make_root.
> >
> > If you are sure about this exchange, I can resubmit a v2 patch.
>
> I think we should just always clean up the allocated memory in
> binderfs_fill_super() when d_make_root() fails and before via a goto
> block after the successful return. So we keep the cleanup in
> binderfs_fill_super() consistent and restricted to a single location.

Hi Christian,

So the final decision is to keep the cleanup or error handling code in
a single goto location at the end of binderfs_fill_super.

If I understand correctly, this change keeps the same semantic as mine
but is more elegant to maintain.