linux-kernel - Re: [PATCH] Devcoredump: fix use-after-free issue when releasing devcd device

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Message-ID: <22ab53d1ae36d4925732e6e1dc989dc75af126da.camel@sipsolutions.net>
Date:   Fri, 27 Oct 2023 14:45:57 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Yu Wang <quic_yyuwang@...cinc.com>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org, kernel@...cinc.com
Subject: Re: [PATCH] Devcoredump: fix use-after-free issue when releasing
 devcd device

On Fri, 2023-10-27 at 13:11 +0200, Greg KH wrote:
> > 
> >     static void my_coredump()
> >     {
> >         struct my_coredump_state dump_state;
> >         struct device *new_device =
> >             kzalloc(sizeof(*new_device), GFP_KERNEL);
> > 
> >         ...
> >         new_device->release = my_dev_release;
> >         device_initialize(new_device);
> >         ...
> >         device_add(new_device);
> >         ...
> >         init_completion(&dump_state.dump_done);
> >         dev_coredumpm(new_device, NULL, &dump_state, datalen, GFP_KERNEL,
> >                       my_coredump_read, my_coredump_free);
> >         wait_for_completion(&dump_state.dump_done);
> >         device_del(new_device);
> >         put_device(new_device);
> >     }
> 
> Is there any in-kernel user like this?  If so, why not fix them up to
> not do this?
> 

Maybe this is only a simplified scenario and whenever you remove a
device when a coredump is still pending this can happen?

Actually, no, wait, what is this doing??? Why is there a completion and
all that stuff there? You shouldn't really care about the dump once you
have created it, and not pass NULL for the struct module pointer
either?!

johannes