linux-kernel - Re: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill

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Date:   Mon, 15 Aug 2022 02:48:27 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Christian Brauner <brauner@...nel.org>,
        Dongliang Mu <mudongliangabcd@...il.com>,
        Dongliang Mu <dzm91@...t.edu.cn>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        syzkaller <syzkaller@...glegroups.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill_super

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.