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Commit c5cff856 authored by Wei Wang's avatar Wei Wang Committed by David S. Miller
Browse files

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: default avatarWei Wang <weiwan@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0c8d2d95

include/net/ip6_fib.h

+29 −1
Original line number Diff line number Diff line
@@ -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)

net/ipv6/ip6_fib.c

+16 −4
Original line number Diff line number Diff line
@@ -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 @@ 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);

		}
@@ -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;

			}

net/ipv6/route.c

+11 −3
Original line number Diff line number Diff line
@@ -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();

		}

	}

}