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xfrm: fix RCU bugs
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This patch reverts commit 5689226 (xfrm: Use rcu_dereference_bh to
deference pointer protected by rcu_read_lock_bh), and fixes bugs
introduced in commit 418a99a ( Replace rwlock on xfrm_policy_afinfo
with rcu )

1) We properly use RCU variant in this file, not a mix of RCU/RCU_BH

2) We must defer some writes after the synchronize_rcu() call or a reader
 can crash dereferencing NULL pointer.

3) Now we use the xfrm_policy_afinfo_lock spinlock only from process
context, we no longer need to block BH in xfrm_policy_register_afinfo()
and xfrm_policy_unregister_afinfo()

4) Can use RCU_INIT_POINTER() instead of rcu_assign_pointer() in
xfrm_policy_unregister_afinfo()

5) Remove a forward inline declaration (xfrm_policy_put_afinfo()),
  and also move xfrm_policy_get_afinfo() declaration.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Fan Du <fan.du@windriver.com>
Cc: Priyanka Jain <Priyanka.Jain@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Eric Dumazet authored and David S. Miller committed Aug 23, 2012
1 parent 0115e8e commit ef8531b
Showing 1 changed file with 39 additions and 37 deletions.
76 changes: 39 additions & 37 deletions net/xfrm/xfrm_policy.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -48,8 +48,6 @@ static struct xfrm_policy_afinfo __rcu *xfrm_policy_afinfo[NPROTO]

static struct kmem_cache *xfrm_dst_cache __read_mostly;

static struct xfrm_policy_afinfo *xfrm_policy_get_afinfo(unsigned short family);
static inline void xfrm_policy_put_afinfo(struct xfrm_policy_afinfo *afinfo);
static void xfrm_init_pmtu(struct dst_entry *dst);
static int stale_bundle(struct dst_entry *dst);
static int xfrm_bundle_ok(struct xfrm_dst *xdst);
Expand Down Expand Up @@ -96,6 +94,24 @@ bool xfrm_selector_match(const struct xfrm_selector *sel, const struct flowi *fl
return false;
}

static struct xfrm_policy_afinfo *xfrm_policy_get_afinfo(unsigned short family)
{
struct xfrm_policy_afinfo *afinfo;

if (unlikely(family >= NPROTO))
return NULL;
rcu_read_lock();
afinfo = rcu_dereference(xfrm_policy_afinfo[family]);
if (unlikely(!afinfo))
rcu_read_unlock();
return afinfo;
}

static void xfrm_policy_put_afinfo(struct xfrm_policy_afinfo *afinfo)
{
rcu_read_unlock();
}

static inline struct dst_entry *__xfrm_dst_lookup(struct net *net, int tos,
const xfrm_address_t *saddr,
const xfrm_address_t *daddr,
Expand Down Expand Up @@ -2421,7 +2437,7 @@ int xfrm_policy_register_afinfo(struct xfrm_policy_afinfo *afinfo)
return -EINVAL;
if (unlikely(afinfo->family >= NPROTO))
return -EAFNOSUPPORT;
spin_lock_bh(&xfrm_policy_afinfo_lock);
spin_lock(&xfrm_policy_afinfo_lock);
if (unlikely(xfrm_policy_afinfo[afinfo->family] != NULL))
err = -ENOBUFS;
else {
Expand All @@ -2444,7 +2460,7 @@ int xfrm_policy_register_afinfo(struct xfrm_policy_afinfo *afinfo)
afinfo->garbage_collect = xfrm_garbage_collect_deferred;
rcu_assign_pointer(xfrm_policy_afinfo[afinfo->family], afinfo);
}
spin_unlock_bh(&xfrm_policy_afinfo_lock);
spin_unlock(&xfrm_policy_afinfo_lock);

rtnl_lock();
for_each_net(net) {
Expand Down Expand Up @@ -2477,23 +2493,26 @@ int xfrm_policy_unregister_afinfo(struct xfrm_policy_afinfo *afinfo)
return -EINVAL;
if (unlikely(afinfo->family >= NPROTO))
return -EAFNOSUPPORT;
spin_lock_bh(&xfrm_policy_afinfo_lock);
spin_lock(&xfrm_policy_afinfo_lock);
if (likely(xfrm_policy_afinfo[afinfo->family] != NULL)) {
if (unlikely(xfrm_policy_afinfo[afinfo->family] != afinfo))
err = -EINVAL;
else {
struct dst_ops *dst_ops = afinfo->dst_ops;
rcu_assign_pointer(xfrm_policy_afinfo[afinfo->family],
NULL);
dst_ops->kmem_cachep = NULL;
dst_ops->check = NULL;
dst_ops->negative_advice = NULL;
dst_ops->link_failure = NULL;
afinfo->garbage_collect = NULL;
}
else
RCU_INIT_POINTER(xfrm_policy_afinfo[afinfo->family],
NULL);
}
spin_unlock(&xfrm_policy_afinfo_lock);
if (!err) {
struct dst_ops *dst_ops = afinfo->dst_ops;

synchronize_rcu();

dst_ops->kmem_cachep = NULL;
dst_ops->check = NULL;
dst_ops->negative_advice = NULL;
dst_ops->link_failure = NULL;
afinfo->garbage_collect = NULL;
}
spin_unlock_bh(&xfrm_policy_afinfo_lock);
synchronize_rcu();
return err;
}
EXPORT_SYMBOL(xfrm_policy_unregister_afinfo);
Expand All @@ -2502,32 +2521,15 @@ static void __net_init xfrm_dst_ops_init(struct net *net)
{
struct xfrm_policy_afinfo *afinfo;

rcu_read_lock_bh();
afinfo = rcu_dereference_bh(xfrm_policy_afinfo[AF_INET]);
rcu_read_lock();
afinfo = rcu_dereference(xfrm_policy_afinfo[AF_INET]);
if (afinfo)
net->xfrm.xfrm4_dst_ops = *afinfo->dst_ops;
#if IS_ENABLED(CONFIG_IPV6)
afinfo = rcu_dereference_bh(xfrm_policy_afinfo[AF_INET6]);
afinfo = rcu_dereference(xfrm_policy_afinfo[AF_INET6]);
if (afinfo)
net->xfrm.xfrm6_dst_ops = *afinfo->dst_ops;
#endif
rcu_read_unlock_bh();
}

static struct xfrm_policy_afinfo *xfrm_policy_get_afinfo(unsigned short family)
{
struct xfrm_policy_afinfo *afinfo;
if (unlikely(family >= NPROTO))
return NULL;
rcu_read_lock();
afinfo = rcu_dereference(xfrm_policy_afinfo[family]);
if (unlikely(!afinfo))
rcu_read_unlock();
return afinfo;
}

static inline void xfrm_policy_put_afinfo(struct xfrm_policy_afinfo *afinfo)
{
rcu_read_unlock();
}

Expand Down

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