act_ife: load meta modules before tcf_idr_check_alloc()

The following deadlock scenario is triggered by syzbot:

Thread A:				Thread B:
tcf_idr_check_alloc()
...
populate_metalist()
  rtnl_unlock()
					rtnl_lock()
					...
  request_module()			tcf_idr_check_alloc()
  rtnl_lock()

At this point, thread A is waiting for thread B to release RTNL
lock, while thread B is waiting for thread A to commit the IDR
change with tcf_idr_insert() later.

Break this deadlock situation by preloading ife modules earlier,
before tcf_idr_check_alloc(), this is fine because we only need
to load modules we need potentially.

Reported-and-tested-by: syzbot+80e32b5d1f9923f8ace6@syzkaller.appspotmail.com
Fixes: 0190c1d452a9 ("net: sched: atomically check-allocate action")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Vlad Buslov <vladbu@mellanox.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
index c1fcd85719d6a7fa86e65ebb89e82e0d931b7ea0..5c568757643b27bbfd31d5991cc6c9b27a5a08bf 100644 (file)
--- a/net/sched/act_ife.c
+++ b/net/sched/act_ife.c
@@ -436,6 +436,25 @@ static void tcf_ife_cleanup(struct tc_action *a)
                kfree_rcu(p, rcu);
 }
 
+static int load_metalist(struct nlattr **tb, bool rtnl_held)
+{
+       int i;
+
+       for (i = 1; i < max_metacnt; i++) {
+               if (tb[i]) {
+                       void *val = nla_data(tb[i]);
+                       int len = nla_len(tb[i]);
+                       int rc;
+
+                       rc = load_metaops_and_vet(i, val, len, rtnl_held);
+                       if (rc != 0)
+                               return rc;
+               }
+       }
+
+       return 0;
+}
+
 static int populate_metalist(struct tcf_ife_info *ife, struct nlattr **tb,
                             bool exists, bool rtnl_held)
 {
@@ -449,10 +468,6 @@ static int populate_metalist(struct tcf_ife_info *ife, struct nlattr **tb,
                        val = nla_data(tb[i]);
                        len = nla_len(tb[i]);
 
-                       rc = load_metaops_and_vet(i, val, len, rtnl_held);
-                       if (rc != 0)
-                               return rc;
-
                        rc = add_metainfo(ife, i, val, len, exists);
                        if (rc)
                                return rc;
@@ -509,6 +524,21 @@ static int tcf_ife_init(struct net *net, struct nlattr *nla,
        if (!p)
                return -ENOMEM;
 
+       if (tb[TCA_IFE_METALST]) {
+               err = nla_parse_nested_deprecated(tb2, IFE_META_MAX,
+                                                 tb[TCA_IFE_METALST], NULL,
+                                                 NULL);
+               if (err) {
+                       kfree(p);
+                       return err;
+               }
+               err = load_metalist(tb2, rtnl_held);
+               if (err) {
+                       kfree(p);
+                       return err;
+               }
+       }
+
        index = parm->index;
        err = tcf_idr_check_alloc(tn, &index, a, bind);
        if (err < 0) {
@@ -570,15 +600,9 @@ static int tcf_ife_init(struct net *net, struct nlattr *nla,
        }
 
        if (tb[TCA_IFE_METALST]) {
-               err = nla_parse_nested_deprecated(tb2, IFE_META_MAX,
-                                                 tb[TCA_IFE_METALST], NULL,
-                                                 NULL);
-               if (err)
-                       goto metadata_parse_err;
                err = populate_metalist(ife, tb2, exists, rtnl_held);
                if (err)
                        goto metadata_parse_err;
-
        } else {
                /* if no passed metadata allow list or passed allow-all
                 * then here we process by adding as many supported metadatum