linux-kernel - RE: [PATCH] net: convert sk_filter.refcnt from atomic_t to refcount

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Date:   Mon, 20 Mar 2017 09:31:56 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "daniel@...earbox.net" <daniel@...earbox.net>
CC:     "ast@...com" <ast@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>
Subject: RE: [PATCH] net: convert sk_filter.refcnt from atomic_t to
 refcount_t

> Hello!
> 
> On 3/18/2017 3:58 PM, Elena Reshetova wrote:
> 
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> >
> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> > Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: David Windsor <dwindsor@...il.com>
> [...]
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index ebaeaf2..62267e2 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> [...]
> > @@ -1179,12 +1179,13 @@ static int __sk_attach_prog(struct bpf_prog *prog,
> struct sock *sk)
> >  		return -ENOMEM;
> >
> >  	fp->prog = prog;
> > -	atomic_set(&fp->refcnt, 0);
> > +	refcount_set(&fp->refcnt, 1);
> >
> >  	if (!sk_filter_charge(sk, fp)) {
> >  		kfree(fp);
> >  		return -ENOMEM;
> >  	}
> > +	refcount_set(&fp->refcnt, 1);
> 
>     Why do it twice?
> 
> [...]
> 
> MBR, Sergei

Sorry I just realized that I had unsquashed changes when I sent this patch, so this is still the old version. 
Will send a new one now. 

Best Regards,
Elena.