netdev - [PATCH net] ipv6: sctp: clone options to avoid use after free

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Date:	Wed, 09 Dec 2015 07:25:06 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	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>,
	Vlad Yasevich <vyasevich@...il.com>,
	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: [PATCH net] ipv6: sctp: clone options to avoid use after free

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>
---
 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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