linux-kernel - Re: [External] Re: [PATCH] driver core: Fix possible use after free on name

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Message-ID: <CAMZfGtUS2_tsf=E3=+O77ooGQUDto0jnt1preWggdar85tb5_A@mail.gmail.com>
Date:   Mon, 6 Apr 2020 19:04:14 +0800
From:   宋牧春 <songmuchun@...edance.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     zhangfeionline@...il.com, rafael@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] driver core: Fix possible use after free
 on name

Hi PengfeiZhang,

Greg KH <gregkh@...uxfoundation.org> 于2020年4月6日周一 上午12:40写道：
>
> On Sun, Apr 05, 2020 at 09:05:49AM -0700, zhangfeionline@...il.com wrote:
> > From: PengfeiZhang <zhangfeionline@...il.com>
> >
> > __class_create() copies the pointer to the name passed as an
> > argument only to be used later. But there's a chance the caller
> > could immediately free the passed string(e.g., local variable).
> > This could trigger a use after free when we use class name(e.g.,
> > dev_uevent_name()called by device_destroy(),class_create_release()).
> >
> > To be on the safe side: duplicate the string with kstrdup_const()
> > so that if an unaware user passes an address to a stack-allocated
> > buffer, we won't get the arbitrary name and crash.
>
> Where are you seeing this happen?
>
> >
> > Signed-off-by: PengfeiZhang <zhangfeionline@...il.com>
> > ---
> >  drivers/base/class.c | 17 +++++++++++++++--
> >  1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/base/class.c b/drivers/base/class.c
> > index bcd410e..770b3b3 100644
> > --- a/drivers/base/class.c
> > +++ b/drivers/base/class.c
> > @@ -206,6 +206,7 @@ void class_unregister(struct class *cls)
> >  static void class_create_release(struct class *cls)
> >  {
> >       pr_debug("%s called for %s\n", __func__, cls->name);
> > +     kfree_const(cls->name);
> >       kfree(cls);
> >  }
> >
> > @@ -227,7 +228,10 @@ struct class *__class_create(struct module *owner, const char *name,
> >                            struct lock_class_key *key)
> >  {
> >       struct class *cls;
> > -     int retval;
> > +     int retval = -EINVAL;
> > +
> > +     if (!name)
> > +             goto done;
>
> This is a new change, who calls this function with name not being set?
>
>
> >
> >       cls = kzalloc(sizeof(*cls), GFP_KERNEL);
> >       if (!cls) {
> > @@ -235,18 +239,27 @@ struct class *__class_create(struct module *owner, const char *name,
> >               goto error;
> >       }
> >
> > +     name = kstrdup_const(name, GFP_KERNEL);
> > +     if (!name) {
> > +             retval = -ENOMEM;
> > +             goto error;
> > +     }
>
> and overwriting the pointer like that is bad-form, try doing something
> else here instead.
>
> > +
> >       cls->name = name;
> >       cls->owner = owner;
> >       cls->class_release = class_create_release;
> >
> >       retval = __class_register(cls, key);
> >       if (retval)
> > -             goto error;
> > +             goto error_class_register;
> >
> >       return cls;
> >
> > +error_class_register:
> > +     kfree(cls->name);
>
> kfree_const()?
>
> thanks,
>
> greg k-h

Yeah, you have some problem with this fix patch which Greg mentioned.
Can you fix it? And
send the fix patch v2 to Greg?

-- 
Yours,
Muchun