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Message-Id: <20170820003408.133176-1-tracywwnj@gmail.com>
Date: Sat, 19 Aug 2017 17:34:08 -0700
From: Wei Wang <weiwan@...gle.com>
To: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Cc: Eric Dumazet <edumazet@...gle.com>,
Martin KaFai Lau <kafai@...com>, Wei Wang <weiwan@...gle.com>
Subject: [PATCH net v2] ipv6: add rcu grace period before freeing fib6_node
From: Wei Wang <weiwan@...gle.com>
We currently keep rt->rt6i_node pointing to the fib6_node for the route.
And some functions make use of this pointer to dereference the fib6_node
from rt structure, e.g. rt6_check(). However, as there is neither
refcount nor rcu taken when dereferencing rt->rt6i_node, it could
potentially cause crashes as rt->rt6i_node could be set to NULL by other
CPUs when doing a route deletion.
This patch introduces an rcu grace period before freeing fib6_node and
makes sure the functions that dereference it takes rcu_read_lock().
Note: there is no "Fixes" tag because this bug was there in a very
early stage.
Signed-off-by: Wei Wang <weiwan@...gle.com>
Acked-by: Eric Dumazet <edumazet@...gle.com>
---
v2: removed one extra empty line
include/net/ip6_fib.h | 30 +++++++++++++++++++++++++++++-
net/ipv6/ip6_fib.c | 20 ++++++++++++++++----
net/ipv6/route.c | 14 +++++++++++---
3 files changed, 56 insertions(+), 8 deletions(-)
diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 71c1646298ae..977a86e3a8d9 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -72,6 +72,7 @@ struct fib6_node {
__u16 fn_flags;
int fn_sernum;
struct rt6_info *rr_ptr;
+ struct rcu_head rcu;
};
#ifndef CONFIG_IPV6_SUBTREES
@@ -171,13 +172,40 @@ static inline void rt6_update_expires(struct rt6_info *rt0, int timeout)
rt0->rt6i_flags |= RTF_EXPIRES;
}
+/* Function to safely get fn->sernum for passed in rt
+ * and store result in passed in cookie.
+ * Return true if we can get cookie safely
+ * Return false if not
+ */
+static inline bool rt6_get_cookie_safe(const struct rt6_info *rt,
+ u32 *cookie)
+{
+ struct fib6_node *fn;
+ bool status = false;
+
+ rcu_read_lock();
+ fn = rcu_dereference(rt->rt6i_node);
+
+ if (fn) {
+ *cookie = fn->fn_sernum;
+ status = true;
+ }
+
+ rcu_read_unlock();
+ return status;
+}
+
static inline u32 rt6_get_cookie(const struct rt6_info *rt)
{
+ u32 cookie = 0;
+
if (rt->rt6i_flags & RTF_PCPU ||
(unlikely(!list_empty(&rt->rt6i_uncached)) && rt->dst.from))
rt = (struct rt6_info *)(rt->dst.from);
- return rt->rt6i_node ? rt->rt6i_node->fn_sernum : 0;
+ rt6_get_cookie_safe(rt, &cookie);
+
+ return cookie;
}
static inline void ip6_rt_put(struct rt6_info *rt)
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 549aacc3cb2c..a9821c230e4e 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -149,11 +149,23 @@ static struct fib6_node *node_alloc(void)
return fn;
}
-static void node_free(struct fib6_node *fn)
+static void node_free_immediate(struct fib6_node *fn)
+{
+ kmem_cache_free(fib6_node_kmem, fn);
+}
+
+static void node_free_rcu(struct rcu_head *head)
{
+ struct fib6_node *fn = container_of(head, struct fib6_node, rcu);
+
kmem_cache_free(fib6_node_kmem, fn);
}
+static void node_free(struct fib6_node *fn)
+{
+ call_rcu(&fn->rcu, node_free_rcu);
+}
+
void rt6_free_pcpu(struct rt6_info *non_pcpu_rt)
{
int cpu;
@@ -697,9 +709,9 @@ static struct fib6_node *fib6_add_1(struct fib6_node *root,
if (!in || !ln) {
if (in)
- node_free(in);
+ node_free_immediate(in);
if (ln)
- node_free(ln);
+ node_free_immediate(ln);
return ERR_PTR(-ENOMEM);
}
@@ -1138,7 +1150,7 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
root, and then (in failure) stale node
in main tree.
*/
- node_free(sfn);
+ node_free_immediate(sfn);
err = PTR_ERR(sn);
goto failure;
}
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index bec12ae3e6b7..4de2d793c4b8 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1289,7 +1289,9 @@ static void rt6_dst_from_metrics_check(struct rt6_info *rt)
static struct dst_entry *rt6_check(struct rt6_info *rt, u32 cookie)
{
- if (!rt->rt6i_node || (rt->rt6i_node->fn_sernum != cookie))
+ u32 rt_cookie;
+
+ if (!rt6_get_cookie_safe(rt, &rt_cookie) || rt_cookie != cookie)
return NULL;
if (rt6_check_expired(rt))
@@ -1357,8 +1359,14 @@ static void ip6_link_failure(struct sk_buff *skb)
if (rt->rt6i_flags & RTF_CACHE) {
if (dst_hold_safe(&rt->dst))
ip6_del_rt(rt);
- } else if (rt->rt6i_node && (rt->rt6i_flags & RTF_DEFAULT)) {
- rt->rt6i_node->fn_sernum = -1;
+ } else {
+ struct fib6_node *fn;
+
+ rcu_read_lock();
+ fn = rcu_dereference(rt->rt6i_node);
+ if (fn && (rt->rt6i_flags & RTF_DEFAULT))
+ fn->fn_sernum = -1;
+ rcu_read_unlock();
}
}
}
--
2.14.1.480.gb18f417b89-goog
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