ipv6: add complete rcu protection around np->opt

[ Upstream commit 45f6fad84cc305103b28d73482b344d7f5b76f39 ]

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>
[bwh: Backported to 3.2:
 - Drop changes to l2tp
 - Fix an additional use of np->opt in tcp_v6_send_synack()
 - Fold in commit 43264e0bd963 ("ipv6: remove unnecessary codes in tcp_ipv6.c")
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

2 files changed, 21 insertions, 2 deletions

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 84b1447481b5..00ef00d0f315 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -369,7 +369,7 @@ struct ipv6_pinfo {
 	struct ipv6_ac_socklist	*ipv6_ac_list;
 	struct ipv6_fl_socklist *ipv6_fl_list;
 
-	struct ipv6_txoptions	*opt;
+	struct ipv6_txoptions __rcu	*opt;
 	struct sk_buff		*pktoptions;
 	struct sk_buff		*rxpmtu;
 	struct {
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 77763c69e0a6..25f04918640e 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -191,6 +191,7 @@ extern rwlock_t ip6_ra_lock;
  */
 
 struct ipv6_txoptions {
+	atomic_t		refcnt;
 	/* Length of this structure */
 	int			tot_len;
 
@@ -203,7 +204,7 @@ 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. */
 };
 
@@ -229,6 +230,24 @@ struct ipv6_fl_socklist {
 	struct ip6_flowlabel	*fl;
 };
 
+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);
+}
+
 extern struct ip6_flowlabel	*fl6_sock_lookup(struct sock *sk, __be32 label);
 extern struct ipv6_txoptions	*fl6_merge_options(struct ipv6_txoptions * opt_space,
 						   struct ip6_flowlabel * fl,