[PATCH v3 net 3/5] ipv6: Fix dst_entry refcnt bugs in ip6_tunnel

Martin KaFai Lau
2015-09-11T18:07:44Z

Problems in the current dst_entry cache in the ip6_tunnel:

1. ip6_tnl_dst_set is racy. There is no lock to protect it:
- One major problem is that the dst refcnt gets messed up. F.e.
the same dst_cache can be released multiple times and then
triggering the infamous dst refcnt < 0 warning message.
- Another issue is the inconsistency between dst_cache and
dst_cookie.

It can be reproduced by adding and removing the ip6gre tunnel
while running a super_netperf TCP_CRR test.

2. ip6_tnl_dst_get does not take the dst refcnt before returning
the dst.

This patch:
1. Create a percpu dst_entry cache in ip6_tnl
2. Use a spinlock to protect the dst_cache operations
3. ip6_tnl_dst_get always takes the dst refcnt before returning

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
include/net/ip6_tunnel.h | 11 ++++-
net/ipv6/ip6_gre.c | 38 ++++++++-------
net/ipv6/ip6_tunnel.c | 122 +++++++++++++++++++++++++++++++++++------------
3 files changed, 123 insertions(+), 48 deletions(-)

diff --git a/include/net/ip6_tunnel.h b/include/net/ip6_tunnel.h
index 979b081..60b4f40 100644
--- a/include/net/ip6_tunnel.h
+++ b/include/net/ip6_tunnel.h
@@ -32,6 +32,12 @@ struct __ip6_tnl_parm {
__be32 o_key;
};

+struct ip6_tnl_dst {
+ spinlock_t lock;
+ struct dst_entry *dst;
+ u32 cookie;
+};
+
/* IPv6 tunnel */
struct ip6_tnl {
struct ip6_tnl __rcu *next; /* next tunnel in list */
@@ -39,8 +45,7 @@ struct ip6_tnl {
struct net *net; /* netns for packet i/o */
struct __ip6_tnl_parm parms; /* tunnel configuration parameters */
struct flowi fl; /* flowi template for xmit */
- struct dst_entry *dst_cache; /* cached dst */
- u32 dst_cookie;
+ struct ip6_tnl_dst __percpu *dst_cache; /* cached dst */

int err_count;
unsigned long err_time;
@@ -61,6 +66,8 @@ struct ipv6_tlv_tnl_enc_lim {
} __packed;

struct dst_entry *ip6_tnl_dst_get(struct ip6_tnl *t);
+int ip6_tnl_dst_init(struct ip6_tnl *t);
+void ip6_tnl_dst_destroy(struct ip6_tnl *t);
void ip6_tnl_dst_reset(struct ip6_tnl *t);
void ip6_tnl_dst_set(struct ip6_tnl *t, struct dst_entry *dst);
int ip6_tnl_rcv_ctl(struct ip6_tnl *t, const struct in6_addr *laddr,
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 24f5dd8..6465124 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -637,17 +637,17 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
dst = ip6_tnl_dst_get(tunnel);

if (!dst) {
- ndst = ip6_route_output(net, NULL, fl6);
+ dst = ip6_route_output(net, NULL, fl6);

- if (ndst->error)
+ if (dst->error)
goto tx_err_link_failure;
- ndst = xfrm_lookup(net, ndst, flowi6_to_flowi(fl6), NULL, 0);
- if (IS_ERR(ndst)) {
- err = PTR_ERR(ndst);
- ndst = NULL;
+ dst = xfrm_lookup(net, dst, flowi6_to_flowi(fl6), NULL, 0);
+ if (IS_ERR(dst)) {
+ err = PTR_ERR(dst);
+ dst = NULL;
goto tx_err_link_failure;
}
- dst = ndst;
+ ndst = dst;
}

tdev = dst->dev;
@@ -702,12 +702,9 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
skb = new_skb;
}

- if (fl6->flowi6_mark) {
- skb_dst_set(skb, dst);
- ndst = NULL;
- } else {
- skb_dst_set_noref(skb, dst);
- }
+ if (!fl6->flowi6_mark && ndst)
+ ip6_tnl_dst_set(tunnel, ndst);
+ skb_dst_set(skb, dst);

proto = NEXTHDR_GRE;
if (encap_limit >= 0) {
@@ -762,14 +759,12 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
skb_set_inner_protocol(skb, protocol);

ip6tunnel_xmit(NULL, skb, dev);
- if (ndst)
- ip6_tnl_dst_set(tunnel, ndst);
return 0;
tx_err_link_failure:
stats->tx_carrier_errors++;
dst_link_failure(skb);
tx_err_dst_release:
- dst_release(ndst);
+ dst_release(dst);
return err;
}

@@ -1223,6 +1218,9 @@ static const struct net_device_ops ip6gre_netdev_ops = {

static void ip6gre_dev_free(struct net_device *dev)
{
+ struct ip6_tnl *t = netdev_priv(dev);
+
+ ip6_tnl_dst_destroy(t);
free_percpu(dev->tstats);
free_netdev(dev);
}
@@ -1248,6 +1246,7 @@ static void ip6gre_tunnel_setup(struct net_device *dev)
static int ip6gre_tunnel_init_common(struct net_device *dev)
{
struct ip6_tnl *tunnel;
+ int ret;

tunnel = netdev_priv(dev);

@@ -1259,6 +1258,13 @@ static int ip6gre_tunnel_init_common(struct net_device *dev)
if (!dev->tstats)
return -ENOMEM;

+ ret = ip6_tnl_dst_init(tunnel);
+ if (ret) {
+ free_percpu(dev->tstats);
+ dev->tstats = NULL;
+ return ret;
+ }
+
return 0;
}

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 599b0b4..851cf6d 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -126,37 +126,90 @@ static struct net_device_stats *ip6_get_stats(struct net_device *dev)
* Locking : hash tables are protected by RCU and RTNL
*/

-struct dst_entry *ip6_tnl_dst_get(struct ip6_tnl *t)
+static void __ip6_tnl_per_cpu_dst_set(struct ip6_tnl_dst *idst,
+ struct dst_entry *dst)
{
- struct dst_entry *dst = t->dst_cache;
-
- if (dst && dst->obsolete &&
- !dst->ops->check(dst, t->dst_cookie)) {
- t->dst_cache = NULL;
- dst_release(dst);
- return NULL;
+ dst_release(idst->dst);
+ if (dst) {
+ dst_hold(dst);
+ idst->cookie = rt6_get_cookie((struct rt6_info *)dst);
+ } else {
+ idst->cookie = 0;
}
+ idst->dst = dst;
+}
+
+static void ip6_tnl_per_cpu_dst_set(struct ip6_tnl_dst *idst,
+ struct dst_entry *dst)
+{

+ spin_lock_bh(&idst->lock);
+ __ip6_tnl_per_cpu_dst_set(idst, dst);
+ spin_unlock_bh(&idst->lock);
+}
+
+struct dst_entry *ip6_tnl_dst_get(struct ip6_tnl *t)
+{
+ struct ip6_tnl_dst *idst;
+ struct dst_entry *dst;
+
+ idst = raw_cpu_ptr(t->dst_cache);
+ spin_lock_bh(&idst->lock);
+ dst = idst->dst;
+ if (dst) {
+ if (!dst->obsolete || dst->ops->check(dst, idst->cookie)) {
+ dst_hold(idst->dst);
+ } else {
+ __ip6_tnl_per_cpu_dst_set(idst, NULL);
+ dst = NULL;
+ }
+ }
+ spin_unlock_bh(&idst->lock);
return dst;
}
EXPORT_SYMBOL_GPL(ip6_tnl_dst_get);

void ip6_tnl_dst_reset(struct ip6_tnl *t)
{
- dst_release(t->dst_cache);
- t->dst_cache = NULL;
+ int i;
+
+ for_each_possible_cpu(i)
+ ip6_tnl_per_cpu_dst_set(raw_cpu_ptr(t->dst_cache), NULL);
}
EXPORT_SYMBOL_GPL(ip6_tnl_dst_reset);

void ip6_tnl_dst_set(struct ip6_tnl *t, struct dst_entry *dst)
{
- struct rt6_info *rt = (struct rt6_info *) dst;
- t->dst_cookie = rt6_get_cookie(rt);
- dst_release(t->dst_cache);
- t->dst_cache = dst;
+ ip6_tnl_per_cpu_dst_set(raw_cpu_ptr(t->dst_cache), dst);
+
}
EXPORT_SYMBOL_GPL(ip6_tnl_dst_set);

+void ip6_tnl_dst_destroy(struct ip6_tnl *t)
+{
+ if (!t->dst_cache)
+ return;
+
+ ip6_tnl_dst_reset(t);
+ free_percpu(t->dst_cache);
+}
+EXPORT_SYMBOL_GPL(ip6_tnl_dst_destroy);
+
+int ip6_tnl_dst_init(struct ip6_tnl *t)
+{
+ int i;
+
+ t->dst_cache = alloc_percpu(struct ip6_tnl_dst);
+ if (!t->dst_cache)
+ return -ENOMEM;
+
+ for_each_possible_cpu(i)
+ spin_lock_init(&per_cpu_ptr(t->dst_cache, i)->lock);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(ip6_tnl_dst_init);
+
/**
* ip6_tnl_lookup - fetch tunnel matching the end-point addresses
* @remote: the address of the tunnel exit-point
@@ -271,6 +324,9 @@ ip6_tnl_unlink(struct ip6_tnl_net *ip6n, struct ip6_tnl *t)

static void ip6_dev_free(struct net_device *dev)
{
+ struct ip6_tnl *t = netdev_priv(dev);
+
+ ip6_tnl_dst_destroy(t);
free_percpu(dev->tstats);
free_netdev(dev);
}
@@ -1016,17 +1072,17 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
goto tx_err_link_failure;

if (!dst) {
- ndst = ip6_route_output(net, NULL, fl6);
+ dst = ip6_route_output(net, NULL, fl6);

- if (ndst->error)
+ if (dst->error)
goto tx_err_link_failure;
- ndst = xfrm_lookup(net, ndst, flowi6_to_flowi(fl6), NULL, 0);
- if (IS_ERR(ndst)) {
- err = PTR_ERR(ndst);
- ndst = NULL;
+ dst = xfrm_lookup(net, dst, flowi6_to_flowi(fl6), NULL, 0);
+ if (IS_ERR(dst)) {
+ err = PTR_ERR(dst);
+ dst = NULL;
goto tx_err_link_failure;
}
- dst = ndst;
+ ndst = dst;
}

tdev = dst->dev;
@@ -1072,12 +1128,11 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
consume_skb(skb);
skb = new_skb;
}
- if (fl6->flowi6_mark) {
- skb_dst_set(skb, dst);
- ndst = NULL;
- } else {
- skb_dst_set_noref(skb, dst);
- }
+
+ if (!fl6->flowi6_mark && ndst)
+ ip6_tnl_dst_set(t, ndst);
+ skb_dst_set(skb, dst);
+
skb->transport_header = skb->network_header;

proto = fl6->flowi6_proto;
@@ -1101,14 +1156,12 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
ipv6h->saddr = fl6->saddr;
ipv6h->daddr = fl6->daddr;
ip6tunnel_xmit(NULL, skb, dev);
- if (ndst)
- ip6_tnl_dst_set(t, ndst);
return 0;
tx_err_link_failure:
stats->tx_carrier_errors++;
dst_link_failure(skb);
tx_err_dst_release:
- dst_release(ndst);
+ dst_release(dst);
return err;
}

@@ -1573,12 +1626,21 @@ static inline int
ip6_tnl_dev_init_gen(struct net_device *dev)
{
struct ip6_tnl *t = netdev_priv(dev);
+ int ret;

t->dev = dev;
t->net = dev_net(dev);
dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
if (!dev->tstats)
return -ENOMEM;
+
+ ret = ip6_tnl_dst_init(t);
+ if (ret) {
+ free_percpu(dev->tstats);
+ dev->tstats = NULL;
+ return ret;
+ }
+
return 0;
}

--
2.5.1