Subject: Re: [PATCH net] ipv6: sctp: clone options to avoid use after free
To: Eric Dumazet <eric.dumazet@gmail.com>, Eric Dumazet <edumazet@google.com>
References: <CACT4Y+YjXJoh3uGDp=FJkYVnjaMxFSPY252ptbDGZ-LQ9JAEWw@mail.gmail.com>
 <CANn89i+V-GeD3zCzGPAo4jY8Z6iTjFN3U1ixG44WyKKLOZ9Txw@mail.gmail.com>
 <20151209145917.GA3884@mrl.redhat.com>
 <CANn89iLhetNbtO6h99zZOrCiMYON50vzVsk7j_AtosXejvvm4Q@mail.gmail.com>
 <1449674706.9768.5.camel@edumazet-glaptop2.roam.corp.google.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        James Morris <jmorris@namei.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Patrick McHardy <kaber@trash.net>, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Neil Horman <nhorman@tuxdriver.com>, linux-sctp@vger.kernel.org,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>
From: Vlad Yasevich <vyasevich@gmail.com>
Message-ID: <566849F9.2090502@gmail.com>
Date: Wed, 9 Dec 2015 10:34:17 -0500
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On 12/09/2015 10:25 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> SCTP is lacking proper np->opt cloning at accept() time.
> 
> TCP and DCCP use ipv6_dup_options() helper, do the same
> in SCTP.
> 
> We might later factorize this code in a common helper to avoid
> future mistakes.
> 
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Acked-by: Vlad Yasevich <vyasevich@gmail.com>

This is sufficient for accept() processing, but looks like peeloff is missing
a bunch of ipv6 support.  I'll see if I can cook something up to fix that part.

-vlad

> ---
>  net/sctp/ipv6.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
> index d28c0b4c9128..ec529121f38a 100644
> --- a/net/sctp/ipv6.c
> +++ b/net/sctp/ipv6.c
> @@ -641,6 +641,7 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
>  	struct sock *newsk;
>  	struct ipv6_pinfo *newnp, *np = inet6_sk(sk);
>  	struct sctp6_sock *newsctp6sk;
> +	struct ipv6_txoptions *opt;
>  
>  	newsk = sk_alloc(sock_net(sk), PF_INET6, GFP_KERNEL, sk->sk_prot, 0);
>  	if (!newsk)
> @@ -660,6 +661,13 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
>  
>  	memcpy(newnp, np, sizeof(struct ipv6_pinfo));
>  
> +	rcu_read_lock();
> +	opt = rcu_dereference(np->opt);
> +	if (opt)
> +		opt = ipv6_dup_options(newsk, opt);
> +	RCU_INIT_POINTER(newnp->opt, opt);
> +	rcu_read_unlock();
> +
>  	/* Initialize sk's sport, dport, rcv_saddr and daddr for getsockname()
>  	 * and getpeername().
>  	 */
> 
> 

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