3.16.50-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Wei Wang <wei...@google.com>
commit c5cff8561d2d0006e972bd114afd51f082fee77c upstream.
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 <wei...@google.com>
Acked-by: Eric Dumazet <eduma...@google.com>
Acked-by: Martin KaFai Lau <ka...@fb.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
include/net/ip6_fib.h | 30 +++++++++++++++++++++++++++++-
net/ipv6/ip6_fib.c | 20 ++++++++++++++++----
net/ipv6/route.c | 14 +++++++++++---
3 files changed, 56 insertions(+), 8 deletions(-)
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -66,6 +66,7 @@ struct fib6_node {
__u16 fn_flags;
__u32 fn_sernum;
struct rt6_info *rr_ptr;
+ struct rcu_head rcu;
};
#ifndef CONFIG_IPV6_SUBTREES
@@ -193,9 +194,36 @@ static inline void rt6_set_from(struct r
rt->dst.from = new;
}
+/* 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)
{
- return rt->rt6i_node ? rt->rt6i_node->fn_sernum : 0;
+ u32 cookie = 0;
+
+ rt6_get_cookie_safe(rt, &cookie);
+
+ return cookie;
}
static inline void ip6_rt_put(struct rt6_info *rt)
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -151,11 +151,23 @@ static __inline__ struct fib6_node *node
return fn;
}
-static __inline__ 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 __inline__ void rt6_release(struct rt6_info *rt)
{
if (atomic_dec_and_test(&rt->rt6i_ref))
@@ -551,9 +563,9 @@ 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);
}
@@ -977,7 +989,7 @@ int fib6_add(struct fib6_node *root, str
root, and then (in st_failure) stale node
in main tree.
*/
- node_free(sfn);
+ node_free_immediate(sfn);
err = PTR_ERR(sn);
goto st_failure;
}
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1090,6 +1090,7 @@ struct dst_entry *ip6_blackhole_route(st
static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
{
struct rt6_info *rt;
+ u32 rt_cookie;
rt = (struct rt6_info *) dst;
@@ -1097,7 +1098,7 @@ static struct dst_entry *ip6_dst_check(s
* DST_OBSOLETE_FORCE_CHK which forces validation calls down
* into this function always.
*/
- if (!rt->rt6i_node || (rt->rt6i_node->fn_sernum != cookie))
+ if (!rt6_get_cookie_safe(rt, &rt_cookie) || rt_cookie != cookie)
return NULL;
if (rt6_check_expired(rt))
@@ -1136,8 +1137,14 @@ static void ip6_link_failure(struct sk_b
dst_hold(&rt->dst);
if (ip6_del_rt(rt))
dst_free(&rt->dst);
- } 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();
}
}
}
