On Tue, Apr 23, 2019 at 09:43:26AM -0700, Eric Dumazet wrote: > Canonical way to fetch sk_user_data from an encap_rcv() handler called > from UDP stack in rcu protected section is to use > rcu_dereference_sk_user_data(), > otherwise compiler might read it multiple times. > That reminds me the more general problem we have with ->sk_user_data: https://lore.kernel.org/netdev/20180117.142538.1972806008716856078.da...@davemloft.net/
We're not even guarateed that ->sk_user_data points to a struct l2tp_tunnel (some external modules can still probably override it). There were some locking rules defined for setting ->sk_user_data: https://lore.kernel.org/netdev/20180124203541.3172-3-...@quantonium.net/ Converting all users to either avoid using ->sk_user_data or using it under the proper pre-conditions has been on my TODO list for a while... I'll try to revive this effort. > Fixes: d00fa9adc528 ("il2tp: fix races with tunnel socket close") ^ Spurious "i". Vi user? :) > Signed-off-by: Eric Dumazet <eduma...@google.com> > Cc: James Chapman <jchap...@katalix.com> > --- > net/l2tp/l2tp_core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c > index > fed6becc5daf86afa2ad9188bb28e151244bb5a6..aee33d1320184e411dbedff72b5bf5199481e53f > 100644 > --- a/net/l2tp/l2tp_core.c > +++ b/net/l2tp/l2tp_core.c > @@ -909,7 +909,7 @@ int l2tp_udp_encap_recv(struct sock *sk, struct sk_buff > *skb) > { > struct l2tp_tunnel *tunnel; > > - tunnel = l2tp_tunnel(sk); > + tunnel = rcu_dereference_sk_user_data(sk); > if (tunnel == NULL) > goto pass_up; > > -- > 2.21.0.593.g511ec345e18-goog >
