From: Martin KaFai Lau kafai@fb.com
[ Upstream commit 886b7a50100a50f1cbd08a6f8ec5884dfbe082dc ]
It is a followup after the fix in commit 9c69a1320515 ("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: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected") Signed-off-by: Martin KaFai Lau kafai@fb.com Acked-by: Wei Wang weiwan@google.com Reviewed-by: David Ahern dsahern@gmail.com Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/route.c | 38 ++++++++++++++++++-------------------- 1 file changed, 18 insertions(+), 20 deletions(-)
--- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -3403,11 +3403,8 @@ static void rt6_do_redirect(struct dst_e
rcu_read_lock(); from = rcu_dereference(rt->from); - /* This fib6_info_hold() is safe here because we hold reference to rt - * and rt already holds reference to fib6_info. - */ - fib6_info_hold(from); - rcu_read_unlock(); + if (!from) + goto out;
nrt = ip6_rt_cache_alloc(from, &msg->dest, NULL); if (!nrt) @@ -3419,10 +3416,7 @@ static void rt6_do_redirect(struct dst_e
nrt->rt6i_gateway = *(struct in6_addr *)neigh->primary_key;
- /* No need to remove rt from the exception table if rt is - * a cached route because rt6_insert_exception() will - * takes care of it - */ + /* rt6_insert_exception() will take care of duplicated exceptions */ if (rt6_insert_exception(nrt, from)) { dst_release_immediate(&nrt->dst); goto out; @@ -3435,7 +3429,7 @@ static void rt6_do_redirect(struct dst_e call_netevent_notifiers(NETEVENT_REDIRECT, &netevent);
out: - fib6_info_release(from); + rcu_read_unlock(); neigh_release(neigh); }
@@ -4957,16 +4951,20 @@ static int inet6_rtm_getroute(struct sk_
rcu_read_lock(); from = rcu_dereference(rt->from); - - if (fibmatch) - err = rt6_fill_node(net, skb, from, NULL, NULL, NULL, iif, - RTM_NEWROUTE, NETLINK_CB(in_skb).portid, - nlh->nlmsg_seq, 0); - else - err = rt6_fill_node(net, skb, from, dst, &fl6.daddr, - &fl6.saddr, iif, RTM_NEWROUTE, - NETLINK_CB(in_skb).portid, nlh->nlmsg_seq, - 0); + if (from) { + if (fibmatch) + err = rt6_fill_node(net, skb, from, NULL, NULL, NULL, + iif, RTM_NEWROUTE, + NETLINK_CB(in_skb).portid, + nlh->nlmsg_seq, 0); + else + err = rt6_fill_node(net, skb, from, dst, &fl6.daddr, + &fl6.saddr, iif, RTM_NEWROUTE, + NETLINK_CB(in_skb).portid, + nlh->nlmsg_seq, 0); + } else { + err = -ENETUNREACH; + } rcu_read_unlock();
if (err < 0) {