ipv6: add rcu grace period before freeing fib6_node

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@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 1a88008cc6f5e14a788491f62ae3c15e47b62c16..e9c59db92942f02a5def4bd45576283c6995f6ad 100644 (file)
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -70,6 +70,7 @@ struct fib6_node {
        __u16                   fn_flags;
        int                     fn_sernum;
        struct rt6_info         *rr_ptr;
+       struct rcu_head         rcu;
 };
 
 #ifndef CONFIG_IPV6_SUBTREES
@@ -167,13 +168,40 @@ 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 5cc0ea0381981b0539d5d6e67401d962a6f6a230..a5ebf86f6be810f23343b7bc824b8587e0c4425a 100644 (file)
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -148,11 +148,23 @@ 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);
+}
+
 static void rt6_free_pcpu(struct rt6_info *non_pcpu_rt)
 {
        int cpu;
@@ -601,9 +613,9 @@ insert_above:
 
                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);
                }
 
@@ -1038,7 +1050,7 @@ 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 94d6a13d47f0e9ec5ff4cbc50b90d4cd9ca3f38a..a9d3564caf49c1906a73266fe1b5a713438d5414 100644 (file)
--- 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();
                }
        }
 }