CVE-2016-3841 (published 2016-08-06T20:59Z)

The IPv6 stack in the Linux kernel before 4.3.3 mishandles options data, which allows local users to gain privileges or cause a denial of service (use-after-free and system crash) via a crafted sendmsg system call.

Severity: HIGH
CVSS v2 base score: 7.2 (AV:L/AC:L/Au:N/C:C/I:C/A:C)
CVSS v3 base score: 7.3, HIGH (CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-264
cwe_name: Permissions, Privileges, and Access Controls
description: Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.
cwe_id: CWE-416
cwe_name: Use After Free
description: The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
extended_description: 
             
             
             
			 
             
             
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Eric Dumazet
author_date: 2015-11-29 19:37:57-08:00
msg: ipv6: add complete rcu protection around np->opt

This patch addresses multiple problems :

UDP/RAW sendmsg() need to get a stable struct ipv6_txoptions
while socket is not locked : Other threads can change np->opt
concurrently. Dmitry posted a syzkaller
(http://github.com/google/syzkaller) program desmonstrating
use-after-free.

Starting with TCP/DCCP lockless listeners, tcp_v6_syn_recv_sock()
and dccp_v6_request_recv_sock() also need to use RCU protection
to dereference np->opt once (before calling ipv6_dup_options())

This patch adds full RCU protection to np->opt

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: ipv6.h
change_type: ModificationType.MODIFY
diff: @@ -227,7 +227,7 @@ struct ipv6_pinfo {
 	struct ipv6_ac_socklist	*ipv6_ac_list;
 	struct ipv6_fl_socklist __rcu *ipv6_fl_list;
 
-	struct ipv6_txoptions	*opt;
+	struct ipv6_txoptions __rcu	*opt;
 	struct sk_buff		*pktoptions;
 	struct sk_buff		*rxpmtu;
 	struct inet6_cork	cork;

programming_language: C
filename: ipv6.h
change_type: ModificationType.MODIFY
diff: @@ -205,6 +205,7 @@ extern rwlock_t ip6_ra_lock;
  */
 
 struct ipv6_txoptions {
+	atomic_t		refcnt;
 	/* Length of this structure */
 	int			tot_len;
 
@@ -217,7 +218,7 @@ struct ipv6_txoptions {
 	struct ipv6_opt_hdr	*dst0opt;
 	struct ipv6_rt_hdr	*srcrt;	/* Routing Header */
 	struct ipv6_opt_hdr	*dst1opt;
-
+	struct rcu_head		rcu;
 	/* Option buffer, as read by IPV6_PKTOPTIONS, starts here. */
 };
 
@@ -252,6 +253,24 @@ struct ipv6_fl_socklist {
 	struct rcu_head			rcu;
 };
 
+static inline struct ipv6_txoptions *txopt_get(const struct ipv6_pinfo *np)
+{
+	struct ipv6_txoptions *opt;
+
+	rcu_read_lock();
+	opt = rcu_dereference(np->opt);
+	if (opt && !atomic_inc_not_zero(&opt->refcnt))
+		opt = NULL;
+	rcu_read_unlock();
+	return opt;
+}
+
+static inline void txopt_put(struct ipv6_txoptions *opt)
+{
+	if (opt && atomic_dec_and_test(&opt->refcnt))
+		kfree_rcu(opt, rcu);
+}
+
 struct ip6_flowlabel *fl6_sock_lookup(struct sock *sk, __be32 label);
 struct ipv6_txoptions *fl6_merge_options(struct ipv6_txoptions *opt_space,
 					 struct ip6_flowlabel *fl,

programming_language: C
filename: ipv6.c
change_type: ModificationType.MODIFY
diff: @@ -202,7 +202,9 @@ static int dccp_v6_send_response(const struct sock *sk, struct request_sock *req
 	security_req_classify_flow(req, flowi6_to_flowi(&fl6));
 
 
-	final_p = fl6_update_dst(&fl6, np->opt, &final);
+	rcu_read_lock();
+	final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
+	rcu_read_unlock();
 
 	dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
 	if (IS_ERR(dst)) {
@@ -219,7 +221,10 @@ static int dccp_v6_send_response(const struct sock *sk, struct request_sock *req
 							 &ireq->ir_v6_loc_addr,
 							 &ireq->ir_v6_rmt_addr);
 		fl6.daddr = ireq->ir_v6_rmt_addr;
-		err = ip6_xmit(sk, skb, &fl6, np->opt, np->tclass);
+		rcu_read_lock();
+		err = ip6_xmit(sk, skb, &fl6, rcu_dereference(np->opt),
+			       np->tclass);
+		rcu_read_unlock();
 		err = net_xmit_eval(err);
 	}
 
@@ -387,6 +392,7 @@ static struct sock *dccp_v6_request_recv_sock(const struct sock *sk,
 	struct inet_request_sock *ireq = inet_rsk(req);
 	struct ipv6_pinfo *newnp;
 	const struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_txoptions *opt;
 	struct inet_sock *newinet;
 	struct dccp6_sock *newdp6;
 	struct sock *newsk;
@@ -488,13 +494,15 @@ static struct sock *dccp_v6_request_recv_sock(const struct sock *sk,
 	 * Yes, keeping reference count would be much more clever, but we make
 	 * one more one thing there: reattach optmem to newsk.
 	 */
-	if (np->opt != NULL)
-		newnp->opt = ipv6_dup_options(newsk, np->opt);
-
+	opt = rcu_dereference(np->opt);
+	if (opt) {
+		opt = ipv6_dup_options(newsk, opt);
+		RCU_INIT_POINTER(newnp->opt, opt);
+	}
 	inet_csk(newsk)->icsk_ext_hdr_len = 0;
-	if (newnp->opt != NULL)
-		inet_csk(newsk)->icsk_ext_hdr_len = (newnp->opt->opt_nflen +
-						     newnp->opt->opt_flen);
+	if (opt)
+		inet_csk(newsk)->icsk_ext_hdr_len = opt->opt_nflen +
+						    opt->opt_flen;
 
 	dccp_sync_mss(newsk, dst_mtu(dst));
 
@@ -757,6 +765,7 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct dccp_sock *dp = dccp_sk(sk);
 	struct in6_addr *saddr = NULL, *final_p, final;
+	struct ipv6_txoptions *opt;
 	struct flowi6 fl6;
 	struct dst_entry *dst;
 	int addr_type;
@@ -856,7 +865,8 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 	fl6.fl6_sport = inet->inet_sport;
 	security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));
 
-	final_p = fl6_update_dst(&fl6, np->opt, &final);
+	opt = rcu_dereference_protected(np->opt, sock_owned_by_user(sk));
+	final_p = fl6_update_dst(&fl6, opt, &final);
 
 	dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
 	if (IS_ERR(dst)) {
@@ -876,9 +886,8 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 	__ip6_dst_store(sk, dst, NULL, NULL);
 
 	icsk->icsk_ext_hdr_len = 0;
-	if (np->opt != NULL)
-		icsk->icsk_ext_hdr_len = (np->opt->opt_flen +
-					  np->opt->opt_nflen);
+	if (opt)
+		icsk->icsk_ext_hdr_len = opt->opt_flen + opt->opt_nflen;
 
 	inet->inet_dport = usin->sin6_port;
 

programming_language: C
filename: af_inet6.c
change_type: ModificationType.MODIFY
diff: @@ -428,9 +428,11 @@ void inet6_destroy_sock(struct sock *sk)
 
 	/* Free tx options */
 
-	opt = xchg(&np->opt, NULL);
-	if (opt)
-		sock_kfree_s(sk, opt, opt->tot_len);
+	opt = xchg((__force struct ipv6_txoptions **)&np->opt, NULL);
+	if (opt) {
+		atomic_sub(opt->tot_len, &sk->sk_omem_alloc);
+		txopt_put(opt);
+	}
 }
 EXPORT_SYMBOL_GPL(inet6_destroy_sock);
 
@@ -659,7 +661,10 @@ int inet6_sk_rebuild_header(struct sock *sk)
 		fl6.fl6_sport = inet->inet_sport;
 		security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));
 
-		final_p = fl6_update_dst(&fl6, np->opt, &final);
+		rcu_read_lock();
+		final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt),
+					 &final);
+		rcu_read_unlock();
 
 		dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
 		if (IS_ERR(dst)) {

programming_language: C
filename: datagram.c
change_type: ModificationType.MODIFY
diff: @@ -167,8 +167,10 @@ static int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int a
 
 	security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));
 
-	opt = flowlabel ? flowlabel->opt : np->opt;
+	rcu_read_lock();
+	opt = flowlabel ? flowlabel->opt : rcu_dereference(np->opt);
 	final_p = fl6_update_dst(&fl6, opt, &final);
+	rcu_read_unlock();
 
 	dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
 	err = 0;

programming_language: C
filename: exthdrs.c
change_type: ModificationType.MODIFY
diff: @@ -727,6 +727,7 @@ ipv6_dup_options(struct sock *sk, struct ipv6_txoptions *opt)
 			*((char **)&opt2->dst1opt) += dif;
 		if (opt2->srcrt)
 			*((char **)&opt2->srcrt) += dif;
+		atomic_set(&opt2->refcnt, 1);
 	}
 	return opt2;
 }
@@ -790,7 +791,7 @@ ipv6_renew_options(struct sock *sk, struct ipv6_txoptions *opt,
 		return ERR_PTR(-ENOBUFS);
 
 	memset(opt2, 0, tot_len);
-
+	atomic_set(&opt2->refcnt, 1);
 	opt2->tot_len = tot_len;
 	p = (char *)(opt2 + 1);
 

programming_language: C
filename: inet6_connection_sock.c
change_type: ModificationType.MODIFY
diff: @@ -78,7 +78,9 @@ struct dst_entry *inet6_csk_route_req(const struct sock *sk,
 	memset(fl6, 0, sizeof(*fl6));
 	fl6->flowi6_proto = proto;
 	fl6->daddr = ireq->ir_v6_rmt_addr;
-	final_p = fl6_update_dst(fl6, np->opt, &final);
+	rcu_read_lock();
+	final_p = fl6_update_dst(fl6, rcu_dereference(np->opt), &final);
+	rcu_read_unlock();
 	fl6->saddr = ireq->ir_v6_loc_addr;
 	fl6->flowi6_oif = ireq->ir_iif;
 	fl6->flowi6_mark = ireq->ir_mark;
@@ -142,7 +144,9 @@ static struct dst_entry *inet6_csk_route_socket(struct sock *sk,
 	fl6->fl6_dport = inet->inet_dport;
 	security_sk_classify_flow(sk, flowi6_to_flowi(fl6));
 
-	final_p = fl6_update_dst(fl6, np->opt, &final);
+	rcu_read_lock();
+	final_p = fl6_update_dst(fl6, rcu_dereference(np->opt), &final);
+	rcu_read_unlock();
 
 	dst = __inet6_csk_dst_check(sk, np->dst_cookie);
 	if (!dst) {
@@ -175,7 +179,8 @@ int inet6_csk_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl_unused
 	/* Restore final destination back after routing done */
 	fl6.daddr = sk->sk_v6_daddr;
 
-	res = ip6_xmit(sk, skb, &fl6, np->opt, np->tclass);
+	res = ip6_xmit(sk, skb, &fl6, rcu_dereference(np->opt),
+		       np->tclass);
 	rcu_read_unlock();
 	return res;
 }

programming_language: C
filename: ipv6_sockglue.c
change_type: ModificationType.MODIFY
diff: @@ -111,7 +111,8 @@ struct ipv6_txoptions *ipv6_update_options(struct sock *sk,
 			icsk->icsk_sync_mss(sk, icsk->icsk_pmtu_cookie);
 		}
 	}
-	opt = xchg(&inet6_sk(sk)->opt, opt);
+	opt = xchg((__force struct ipv6_txoptions **)&inet6_sk(sk)->opt,
+		   opt);
 	sk_dst_reset(sk);
 
 	return opt;
@@ -231,9 +232,12 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 				sk->sk_socket->ops = &inet_dgram_ops;
 				sk->sk_family = PF_INET;
 			}
-			opt = xchg(&np->opt, NULL);
-			if (opt)
-				sock_kfree_s(sk, opt, opt->tot_len);
+			opt = xchg((__force struct ipv6_txoptions **)&np->opt,
+				   NULL);
+			if (opt) {
+				atomic_sub(opt->tot_len, &sk->sk_omem_alloc);
+				txopt_put(opt);
+			}
 			pktopt = xchg(&np->pktoptions, NULL);
 			kfree_skb(pktopt);
 
@@ -403,7 +407,8 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		if (optname != IPV6_RTHDR && !ns_capable(net->user_ns, CAP_NET_RAW))
 			break;
 
-		opt = ipv6_renew_options(sk, np->opt, optname,
+		opt = rcu_dereference_protected(np->opt, sock_owned_by_user(sk));
+		opt = ipv6_renew_options(sk, opt, optname,
 					 (struct ipv6_opt_hdr __user *)optval,
 					 optlen);
 		if (IS_ERR(opt)) {
@@ -432,8 +437,10 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		retv = 0;
 		opt = ipv6_update_options(sk, opt);
 sticky_done:
-		if (opt)
-			sock_kfree_s(sk, opt, opt->tot_len);
+		if (opt) {
+			atomic_sub(opt->tot_len, &sk->sk_omem_alloc);
+			txopt_put(opt);
+		}
 		break;
 	}
 
@@ -486,6 +493,7 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 			break;
 
 		memset(opt, 0, sizeof(*opt));
+		atomic_set(&opt->refcnt, 1);
 		opt->tot_len = sizeof(*opt) + optlen;
 		retv = -EFAULT;
 		if (copy_from_user(opt+1, optval, optlen))
@@ -502,8 +510,10 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		retv = 0;
 		opt = ipv6_update_options(sk, opt);
 done:
-		if (opt)
-			sock_kfree_s(sk, opt, opt->tot_len);
+		if (opt) {
+			atomic_sub(opt->tot_len, &sk->sk_omem_alloc);
+			txopt_put(opt);
+		}
 		break;
 	}
 	case IPV6_UNICAST_HOPS:
@@ -1110,10 +1120,11 @@ static int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
 	case IPV6_RTHDR:
 	case IPV6_DSTOPTS:
 	{
+		struct ipv6_txoptions *opt;
 
 		lock_sock(sk);
-		len = ipv6_getsockopt_sticky(sk, np->opt,
-					     optname, optval, len);
+		opt = rcu_dereference_protected(np->opt, sock_owned_by_user(sk));
+		len = ipv6_getsockopt_sticky(sk, opt, optname, optval, len);
 		release_sock(sk);
 		/* check if ipv6_getsockopt_sticky() returns err code */
 		if (len < 0)

programming_language: C
filename: raw.c
change_type: ModificationType.MODIFY
diff: @@ -733,6 +733,7 @@ static int raw6_getfrag(void *from, char *to, int offset, int len, int odd,
 
 static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
+	struct ipv6_txoptions *opt_to_free = NULL;
 	struct ipv6_txoptions opt_space;
 	DECLARE_SOCKADDR(struct sockaddr_in6 *, sin6, msg->msg_name);
 	struct in6_addr *daddr, *final_p, final;
@@ -839,8 +840,10 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		if (!(opt->opt_nflen|opt->opt_flen))
 			opt = NULL;
 	}
-	if (!opt)
-		opt = np->opt;
+	if (!opt) {
+		opt = txopt_get(np);
+		opt_to_free = opt;
+		}
 	if (flowlabel)
 		opt = fl6_merge_options(&opt_space, flowlabel, opt);
 	opt = ipv6_fixup_options(&opt_space, opt);
@@ -906,6 +909,7 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	dst_release(dst);
 out:
 	fl6_sock_release(flowlabel);
+	txopt_put(opt_to_free);
 	return err < 0 ? err : len;
 do_confirm:
 	dst_confirm(dst);

programming_language: C
filename: syncookies.c
change_type: ModificationType.MODIFY
diff: @@ -222,7 +222,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		memset(&fl6, 0, sizeof(fl6));
 		fl6.flowi6_proto = IPPROTO_TCP;
 		fl6.daddr = ireq->ir_v6_rmt_addr;
-		final_p = fl6_update_dst(&fl6, np->opt, &final);
+		final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
 		fl6.saddr = ireq->ir_v6_loc_addr;
 		fl6.flowi6_oif = sk->sk_bound_dev_if;
 		fl6.flowi6_mark = ireq->ir_mark;

programming_language: C
filename: tcp_ipv6.c
change_type: ModificationType.MODIFY
diff: @@ -120,6 +120,7 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct in6_addr *saddr = NULL, *final_p, final;
+	struct ipv6_txoptions *opt;
 	struct flowi6 fl6;
 	struct dst_entry *dst;
 	int addr_type;
@@ -235,7 +236,8 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 	fl6.fl6_dport = usin->sin6_port;
 	fl6.fl6_sport = inet->inet_sport;
 
-	final_p = fl6_update_dst(&fl6, np->opt, &final);
+	opt = rcu_dereference_protected(np->opt, sock_owned_by_user(sk));
+	final_p = fl6_update_dst(&fl6, opt, &final);
 
 	security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));
 
@@ -263,9 +265,9 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 		tcp_fetch_timewait_stamp(sk, dst);
 
 	icsk->icsk_ext_hdr_len = 0;
-	if (np->opt)
-		icsk->icsk_ext_hdr_len = (np->opt->opt_flen +
-					  np->opt->opt_nflen);
+	if (opt)
+		icsk->icsk_ext_hdr_len = opt->opt_flen +
+					 opt->opt_nflen;
 
 	tp->rx_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);
 
@@ -461,7 +463,8 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
 		if (np->repflow && ireq->pktopts)
 			fl6->flowlabel = ip6_flowlabel(ipv6_hdr(ireq->pktopts));
 
-		err = ip6_xmit(sk, skb, fl6, np->opt, np->tclass);
+		err = ip6_xmit(sk, skb, fl6, rcu_dereference(np->opt),
+			       np->tclass);
 		err = net_xmit_eval(err);
 	}
 
@@ -972,6 +975,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 	struct inet_request_sock *ireq;
 	struct ipv6_pinfo *newnp;
 	const struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_txoptions *opt;
 	struct tcp6_sock *newtcp6sk;
 	struct inet_sock *newinet;
 	struct tcp_sock *newtp;
@@ -1098,13 +1102,15 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 	   but we make one more one thing there: reattach optmem
 	   to newsk.
 	 */
-	if (np->opt)
-		newnp->opt = ipv6_dup_options(newsk, np->opt);
-
+	opt = rcu_dereference(np->opt);
+	if (opt) {
+		opt = ipv6_dup_options(newsk, opt);
+		RCU_INIT_POINTER(newnp->opt, opt);
+	}
 	inet_csk(newsk)->icsk_ext_hdr_len = 0;
-	if (newnp->opt)
-		inet_csk(newsk)->icsk_ext_hdr_len = (newnp->opt->opt_nflen +
-						     newnp->opt->opt_flen);
+	if (opt)
+		inet_csk(newsk)->icsk_ext_hdr_len = opt->opt_nflen +
+						    opt->opt_flen;
 
 	tcp_ca_openreq_child(newsk, dst);
 

programming_language: C
filename: udp.c
change_type: ModificationType.MODIFY
diff: @@ -1110,6 +1110,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	DECLARE_SOCKADDR(struct sockaddr_in6 *, sin6, msg->msg_name);
 	struct in6_addr *daddr, *final_p, final;
 	struct ipv6_txoptions *opt = NULL;
+	struct ipv6_txoptions *opt_to_free = NULL;
 	struct ip6_flowlabel *flowlabel = NULL;
 	struct flowi6 fl6;
 	struct dst_entry *dst;
@@ -1263,8 +1264,10 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			opt = NULL;
 		connected = 0;
 	}
-	if (!opt)
-		opt = np->opt;
+	if (!opt) {
+		opt = txopt_get(np);
+		opt_to_free = opt;
+	}
 	if (flowlabel)
 		opt = fl6_merge_options(&opt_space, flowlabel, opt);
 	opt = ipv6_fixup_options(&opt_space, opt);
@@ -1373,6 +1376,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 out:
 	dst_release(dst);
 	fl6_sock_release(flowlabel);
+	txopt_put(opt_to_free);
 	if (!err)
 		return len;
 	/*

programming_language: C
filename: l2tp_ip6.c
change_type: ModificationType.MODIFY
diff: @@ -486,6 +486,7 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	DECLARE_SOCKADDR(struct sockaddr_l2tpip6 *, lsa, msg->msg_name);
 	struct in6_addr *daddr, *final_p, final;
 	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_txoptions *opt_to_free = NULL;
 	struct ipv6_txoptions *opt = NULL;
 	struct ip6_flowlabel *flowlabel = NULL;
 	struct dst_entry *dst = NULL;
@@ -575,8 +576,10 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			opt = NULL;
 	}
 
-	if (opt == NULL)
-		opt = np->opt;
+	if (!opt) {
+		opt = txopt_get(np);
+		opt_to_free = opt;
+	}
 	if (flowlabel)
 		opt = fl6_merge_options(&opt_space, flowlabel, opt);
 	opt = ipv6_fixup_options(&opt_space, opt);
@@ -631,6 +634,7 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	dst_release(dst);
 out:
 	fl6_sock_release(flowlabel);
+	txopt_put(opt_to_free);
 
 	return err < 0 ? err : len;
 

programming_language: C