[PATCH 4.3 31/55] ipv6: sctp: clone options to avoid use after free

[Greg Kroah-Hartman]

4.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 9470e24f35ab81574da54e69df90c1eb4a96b43f ]

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@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Acked-by: Vlad Yasevich <vyasevich@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/sctp/ipv6.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -635,6 +635,7 @@ static struct sock *sctp_v6_create_accep
 	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)
@@ -654,6 +655,13 @@ static struct sock *sctp_v6_create_accep
 
 	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().
 	 */