linux-kernel - RE: [PATCH] fs, cifs: convert tcon_link.tl_count from atomic_t to refcount

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Message-ID: <2236FBA76BA1254E88B949DDB74E612B802B7A69@IRSMSX102.ger.corp.intel.com>
Date:   Tue, 31 Oct 2017 09:41:46 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Aurélien Aptel <aaptel@...e.com>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sfrench@...ba.org" <sfrench@...ba.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>
Subject: RE: [PATCH] fs, cifs: convert tcon_link.tl_count from atomic_t to
 refcount_t


> Elena Reshetova <elena.reshetova@...el.com> writes:
> > atomic_t variables are currently used to implement reference
> > counters with the following properties:
> >  - counter is initialized to 1 using atomic_set()
> >  - a resource is freed upon counter reaching zero
> >  - once counter reaches zero, its further
> >    increments aren't allowed
> >  - counter schema uses basic atomic operations
> >    (set, inc, inc_not_zero, dec_and_test, etc.)
> >
> > Such atomic variables should be converted to a newly provided
> > refcount_t type and API that prevents accidental counter overflows
> > and underflows. This is important since overflows and underflows
> > can lead to use-after-free situation and be exploitable.
> >
> > The variable tcon_link.tl_count is used as pure reference counter.
> > Convert it to refcount_t and fix up the operations.
> 
> <snip>
> 
> > -		cifs_get_tlink(tlink);
> > +		refcount_set(&tlink->tl_count, 1);
> 
> Since cifs_get_tlink() basically only increments the reference count and
> given that this is a new tlink I also think this replacement is ok.
> 
> Looks good to me and passes 'make C=1'.
> 
> Reviewed-by: Aurelien Aptel <aaptel@...e.com>

Thank you very much for your review Aurelien! 
Do you know who would be the person to take this patch further?

Best Regards,
Elena.

> 
> --
> Aurélien Aptel / SUSE Labs Samba Team
> GPG: 1839 CB5F 9F5B FB9B AA97  8C99 03C8 A49B 521B D5D3
> SUSE Linux GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
> GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)