net: convert sk_filter.refcnt from atomic_t to refcount_t

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@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 include/linux/filter.h |  3 ++-
 net/core/filter.c      | 17 ++++++++++++-----
 2 files changed, 14 insertions(+), 6 deletions(-)

On 03/20/2017 10:37 AM, Elena Reshetova wrote:
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index ebaeaf2..389cb8d 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -928,7 +928,7 @@ static void sk_filter_release_rcu(struct rcu_head *rcu)
>    */
>   static void sk_filter_release(struct sk_filter *fp)
>   {
> -	if (atomic_dec_and_test(&fp->refcnt))
> +	if (refcount_dec_and_test(&fp->refcnt))
>   		call_rcu(&fp->rcu, sk_filter_release_rcu);
>   }
>
> @@ -943,20 +943,27 @@ void sk_filter_uncharge(struct sock *sk, struct sk_filter *fp)
>   /* try to charge the socket memory if there is space available
>    * return true on success
>    */
> -bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
> +bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp)

And this then becomes: static bool __sk_filter_charge(...)

>   {
>   	u32 filter_size = bpf_prog_size(fp->prog->len);
>
>   	/* same check as in sock_kmalloc() */
>   	if (filter_size <= sysctl_optmem_max &&
>   	    atomic_read(&sk->sk_omem_alloc) + filter_size < sysctl_optmem_max) {
> -		atomic_inc(&fp->refcnt);
>   		atomic_add(filter_size, &sk->sk_omem_alloc);
>   		return true;
>   	}
>   	return false;
>   }

Since here is just all in slow-path, looks fine to me if the above
is addressed as well in v3:

Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Please make sure you add [PATCH net-next] in your subject in future
so that it's clear which tree this goes to.

Thanks,
Daniel

> On 03/20/2017 10:37 AM, Elena Reshetova wrote:
> [...]
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index ebaeaf2..389cb8d 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -928,7 +928,7 @@ static void sk_filter_release_rcu(struct rcu_head *rcu)
> >    */
> >   static void sk_filter_release(struct sk_filter *fp)
> >   {
> > -	if (atomic_dec_and_test(&fp->refcnt))
> > +	if (refcount_dec_and_test(&fp->refcnt))
> >   		call_rcu(&fp->rcu, sk_filter_release_rcu);
> >   }
> >
> > @@ -943,20 +943,27 @@ void sk_filter_uncharge(struct sock *sk, struct
> sk_filter *fp)
> >   /* try to charge the socket memory if there is space available
> >    * return true on success
> >    */
> > -bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
> > +bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp)
> 
> And this then becomes: static bool __sk_filter_charge(...)

Ups, I guess I am getting too tired of all these patch sendings, so more and more mistakes slide in. 
Will try switching to smth else to get attention back in order. 

> 
> >   {
> >   	u32 filter_size = bpf_prog_size(fp->prog->len);
> >
> >   	/* same check as in sock_kmalloc() */
> >   	if (filter_size <= sysctl_optmem_max &&
> >   	    atomic_read(&sk->sk_omem_alloc) + filter_size <
> sysctl_optmem_max) {
> > -		atomic_inc(&fp->refcnt);
> >   		atomic_add(filter_size, &sk->sk_omem_alloc);
> >   		return true;
> >   	}
> >   	return false;
> >   }
> 
> Since here is just all in slow-path, looks fine to me if the above
> is addressed as well in v3:
> 
> Acked-by: Daniel Borkmann <daniel@iogearbox.net>
> 
> Please make sure you add [PATCH net-next] in your subject in future
> so that it's clear which tree this goes to.

Thank you very much! Will do. 

Best Regards,
Elena.
> 
> Thanks,
> Daniel