linux-kernel - Re: KASAN: use-after-free Read in fuse_dev_do

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Message-ID: <CAJfpeguTiN22KqMCH9NMs0Hj+ZcshdzFUk7Mb38Jt0ewHEOHpg@mail.gmail.com>
Date:   Mon, 24 Sep 2018 16:27:21 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     syzbot <syzbot+4e975615ca01f2277bdd@...kaller.appspotmail.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in fuse_dev_do_read

On Mon, Sep 24, 2018 at 2:06 PM, Kirill Tkhai <ktkhai@...tuozzo.com> wrote:

> Fix from my previous message makes the use-after-free does not reproduce
> with the reproducer in my setup.

Excellent.

>
> I can prepare the patch, but before this some comments from Miklos would
> be welcome.
>
> Miklos, what you think about this?

I like the patch.

We could optimize away the get/put by moving the set_bit/test_bit part
inside the fpq->lock-ed region and only get the refcount for the
(unlikely) interrupted case.  OTOH it's probably not worth the extra
complexity, so let's stay with this simpler fix.

Thanks,
Miklos