On Mon 09 Jul 2018 at 20:34, Marcelo Ricardo Leitner <marcelo.leit...@gmail.com> wrote: > On Mon, Jul 09, 2018 at 08:26:47PM +0300, Vlad Buslov wrote: >> Fix action attribute size calculation function to take rcu read lock and >> access act_cookie pointer with rcu dereference. >> >> Fixes: eec94fdb0480 ("net: sched: use rcu for action cookie update") >> Reported-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com> >> Signed-off-by: Vlad Buslov <vla...@mellanox.com> >> --- >> net/sched/act_api.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/net/sched/act_api.c b/net/sched/act_api.c >> index 66dc19746c63..148a89ab789b 100644 >> --- a/net/sched/act_api.c >> +++ b/net/sched/act_api.c >> @@ -149,10 +149,15 @@ EXPORT_SYMBOL(__tcf_idr_release); >> >> static size_t tcf_action_shared_attrs_size(const struct tc_action *act) >> { >> + struct tc_cookie *act_cookie; >> u32 cookie_len = 0; >> >> - if (act->act_cookie) >> - cookie_len = nla_total_size(act->act_cookie->len); >> + rcu_read_lock(); >> + act_cookie = rcu_dereference(act->act_cookie); >> + >> + if (act_cookie) >> + cookie_len = nla_total_size(act_cookie->len); >> + rcu_read_unlock(); > > I am not sure if this is enough to fix the entire issue. Now it will > fetch the length correctly but, what guarantees that when it tries to > actually copy the key (tcf_action_dump_1), the same act_cookie pointer > will be used? As in, can't the new re-fetch be different/smaller than > the object used here?
I checked the code of nlmsg_put() and similar functions, and they check that there is enough free space at skb tailroom. If not, they fail gracefully and return error. Am I missing something? > >> >> return nla_total_size(0) /* action number nested */ >> + nla_total_size(IFNAMSIZ) /* TCA_ACT_KIND */ >> -- >> 2.7.5 >>