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

From: Al Viro <viro@zeniv.linux.org.uk>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Christian Brauner" <brauner@kernel.org>,
	"Dongliang Mu" <mudongliangabcd@gmail.com>,
	"Dongliang Mu" <dzm91@hust.edu.cn>,
	"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 02:48:27 +0100	[thread overview]
Message-ID: <Yvml67jphhmGXUFN@ZenIV> (raw)
In-Reply-To: <YvmlfBJTiOQVfVtX@ZenIV>

On Mon, Aug 15, 2022 at 02:46:36AM +0100, Al Viro wrote:
> On Fri, Aug 12, 2022 at 04:32:28PM +0200, Greg Kroah-Hartman wrote:
> 
> > > It's a bit tricky to follow but d_make_root() always consumes the inode.
> > > On success via d_instantiate() and on failure via iput(). So when
> > > d_make_root() has been called the inode is off limits. And as soon as
> > > d_make_root() has returned successfully we're guaranteed that
> > > sb->s_fs_info is cleaned up if a ->put_super() method has been defined.
> > > Just fyi.
> > 
> > Ah, thanks, that wasn't obvious at all.
> > 
> > greg k-h
> 
> FWIW, I would rather provide a proper ->kill_sb() and gotten rid of
> all that stuff.  The thing is, unlike ->put_super(), ->kill_sb() is
> called for *anything* that has gotten to foo_fill_super().  Usually
> allows to get rid of those "call all of or parts of foo_put_super()
> on failure exits" and associated bitrot...
> 
> Like this (completely untested):

[snip the patch]

PS: that's instead of the patch upstream, not on top of it.