linux-kernel - Re: [PATCH net] ipv6: sctp: clone options to avoid use after free

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Date:	Wed, 9 Dec 2015 10:34:17 -0500
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Eric Dumazet <edumazet@...gle.com>
Cc:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Neil Horman <nhorman@...driver.com>,
	linux-sctp@...r.kernel.org, syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH net] ipv6: sctp: clone options to avoid use after free

On 12/09/2015 10:25 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.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@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Acked-by: Vlad Yasevich <vyasevich@...il.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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