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>
This commit is contained in:
Wei Wang 2017-08-21 09:47:10 -07:00 коммит произвёл David S. Miller
Родитель 0c8d2d95b8
Коммит c5cff8561d
3 изменённых файлов: 56 добавлений и 8 удалений

Просмотреть файл

@ -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)

Просмотреть файл

@ -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;
}

Просмотреть файл

@ -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();
}
}
}