Commit 886b7a50 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by David S. Miller
Browse files

ipv6: A few fixes on dereferencing rt->from 



It is a followup after the fix in
commit 9c69a132 ("route: Avoid crash from dereferencing NULL rt->from")

rt6_do_redirect():
1. NULL checking is needed on rt->from because a parallel
   fib6_info delete could happen that sets rt->from to NULL.
   (e.g. rt6_remove_exception() and fib6_drop_pcpu_from()).

2. fib6_info_hold() is not enough.  Same reason as (1).
   Meaning, holding dst->__refcnt cannot ensure
   rt->from is not NULL or rt->from->fib6_ref is not 0.

   Instead of using fib6_info_hold_safe() which ip6_rt_cache_alloc()
   is already doing, this patch chooses to extend the rcu section
   to keep "from" dereference-able after checking for NULL.

inet6_rtm_getroute():
1. NULL checking is also needed on rt->from for a similar reason.
   Note that inet6_rtm_getroute() is using RTNL_FLAG_DOIT_UNLOCKED.

Fixes: a68886a6 ("net/ipv6: Make from in rt6_info rcu protected")
Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Acked-by: default avatarWei Wang <weiwan@google.com>
Reviewed-by: default avatarDavid Ahern <dsahern@gmail.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f3505745

net/ipv6/route.c

+18 −20
Original line number Original line Diff line number Diff line
@@ -3392,11 +3392,8 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu 




	rcu_read_lock();

	rcu_read_lock();

	from = rcu_dereference(rt->from);

	from = rcu_dereference(rt->from);

	/* This fib6_info_hold() is safe here because we hold reference to rt

	if (!from)

	 * and rt already holds reference to fib6_info.

		goto out;

	 */

	fib6_info_hold(from);

	rcu_read_unlock();





	nrt = ip6_rt_cache_alloc(from, &msg->dest, NULL);

	nrt = ip6_rt_cache_alloc(from, &msg->dest, NULL);

	if (!nrt)

	if (!nrt)
@@ -3408,10 +3405,7 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu 




	nrt->rt6i_gateway = *(struct in6_addr *)neigh->primary_key;

	nrt->rt6i_gateway = *(struct in6_addr *)neigh->primary_key;





	/* No need to remove rt from the exception table if rt is

	/* rt6_insert_exception() will take care of duplicated exceptions */

	 * a cached route because rt6_insert_exception() will

	 * takes care of it

	 */

	if (rt6_insert_exception(nrt, from)) {

	if (rt6_insert_exception(nrt, from)) {

		dst_release_immediate(&nrt->dst);

		dst_release_immediate(&nrt->dst);

		goto out;

		goto out;
@@ -3424,7 +3418,7 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu 
	call_netevent_notifiers(NETEVENT_REDIRECT, &netevent);

	call_netevent_notifiers(NETEVENT_REDIRECT, &netevent);





out:

out:

	fib6_info_release(from);

	rcu_read_unlock();

	neigh_release(neigh);

	neigh_release(neigh);

}

}
@@ -5023,16 +5017,20 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh, 




	rcu_read_lock();

	rcu_read_lock();

	from = rcu_dereference(rt->from);

	from = rcu_dereference(rt->from);



	if (from) {

		if (fibmatch)

		if (fibmatch)

		err = rt6_fill_node(net, skb, from, NULL, NULL, NULL, iif,

			err = rt6_fill_node(net, skb, from, NULL, NULL, NULL,

				    RTM_NEWROUTE, NETLINK_CB(in_skb).portid,

					    iif, RTM_NEWROUTE,

					    NETLINK_CB(in_skb).portid,

					    nlh->nlmsg_seq, 0);

					    nlh->nlmsg_seq, 0);

		else

		else

			err = rt6_fill_node(net, skb, from, dst, &fl6.daddr,

			err = rt6_fill_node(net, skb, from, dst, &fl6.daddr,

					    &fl6.saddr, iif, RTM_NEWROUTE,

					    &fl6.saddr, iif, RTM_NEWROUTE,

				    NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,

					    NETLINK_CB(in_skb).portid,

				    0);

					    nlh->nlmsg_seq, 0);

	} else {

		err = -ENETUNREACH;

	}

	rcu_read_unlock();

	rcu_read_unlock();





	if (err < 0) {

	if (err < 0) {

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