linux-kernel - Re: [PATCH 1/2] pstore: check PSTORE_FLAGS_FRAGILE in pstore

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Date:	Sun, 25 Oct 2015 10:22:32 +0800
From:	Geliang Tang <geliangtang@....com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Anton Vorontsov <anton@...msg.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	Geliang Tang <geliangtang@....com>
Subject: Re: [PATCH 1/2] pstore: check PSTORE_FLAGS_FRAGILE in
 pstore_unregister

On Fri, Oct 23, 2015 at 09:54:31AM -0700, Kees Cook wrote:
> On Fri, Oct 23, 2015 at 7:56 AM, Geliang Tang <geliangtang@....com> wrote:
> > When PSTORE_FLAGS_FRAGILE flag is set, only kmsg is registered in
> > pstore_register. So, under these circumstances, only kmsg needs to
> > be unregistered in pstore_unregister.
> >
> > Signed-off-by: Geliang Tang <geliangtang@....com>
> 
> Would it make more sense to have the pstore_unregister_* calls be
> defensive, like kfree() is? In other words, it would be safe to call
> them, even if they hadn't been registered?
> 
> Either way, I'm fine with this. Good catch!
> 
> -Kees
> 

Thanks for your reply.

pstore_unregister_* is defensive as you expected. I have tested it. it
is safe to call them if they haven't been registered. This won't cause
any trouble.

But logically, we should check this flag in pstore_unregister.

-Geliang Tang

> > ---
> >  fs/pstore/platform.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> > index 0aab920..7ad2038 100644
> > --- a/fs/pstore/platform.c
> > +++ b/fs/pstore/platform.c
> > @@ -496,9 +496,12 @@ EXPORT_SYMBOL_GPL(pstore_register);
> >
> >  void pstore_unregister(struct pstore_info *psi)
> >  {
> > -       pstore_unregister_pmsg();
> > -       pstore_unregister_ftrace();
> > -       pstore_unregister_console();
> > +       if ((psi->flags & PSTORE_FLAGS_FRAGILE) == 0) {
> > +               pstore_unregister_pmsg();
> > +               pstore_unregister_ftrace();
> > +               pstore_unregister_console();
> > +       }
> > +
> >         pstore_unregister_kmsg();
> >
> >         free_buf_for_compression();
> > --
> > 2.5.0
> >
> >
> 
> 
> 
> -- 
> Kees Cook
> Chrome OS Security

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