[PATCH RFC 4/5] net/sched: act_csum: validate the control action inside init()

[Davide Caratti]

Don't overwrite act_csum data if the control control action is not valid,
to prevent loosing the previous configuration in case validation failed.
Not doing that caused NULL dereference in the data path if 'goto chain'
is used.

Tested with:
 # ./tdc.py -c csum

Fixes: db50514f9a9c ("net: sched: add termination action to allow goto chain")
Fixes: 97763dc0f401 ("net_sched: reject unknown tcfa_action values")
Signed-off-by: Davide Caratti <dcara...@redhat.com>
---
 net/sched/act_csum.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/net/sched/act_csum.c b/net/sched/act_csum.c
index 1ae120c9ab02..bf0940156886 100644
--- a/net/sched/act_csum.c
+++ b/net/sched/act_csum.c
@@ -33,6 +33,7 @@
 #include <net/sctp/checksum.h>
 
 #include <net/act_api.h>
+#include <net/pkt_cls.h>
 
 #include <linux/tc_act/tc_csum.h>
 #include <net/tc_act/tc_csum.h>
@@ -52,6 +53,7 @@ static int tcf_csum_init(struct net *net, struct nlattr *nla,
        struct tc_action_net *tn = net_generic(net, csum_net_id);
        struct tcf_csum_params *params_new;
        struct nlattr *tb[TCA_CSUM_MAX + 1];
+       struct tcf_chain *newchain = NULL;
        struct tc_csum *parm;
        struct tcf_csum *p;
        int ret = 0, err;
@@ -87,17 +89,23 @@ static int tcf_csum_init(struct net *net, struct nlattr 
*nla,
                return err;
        }
 
+       err = tcf_action_check_ctrlact(parm->action, tp, &newchain, extack);
+       if (unlikely(err)) {
+               ret = err;
+               goto error;
+       }
+
        p = to_tcf_csum(*a);
 
        params_new = kzalloc(sizeof(*params_new), GFP_KERNEL);
        if (unlikely(!params_new)) {
-               tcf_idr_release(*a, bind);
-               return -ENOMEM;
+               ret = -ENOMEM;
+               goto error;
        }
        params_new->update_flags = parm->update_flags;
 
        spin_lock_bh(&p->tcf_lock);
-       p->tcf_action = parm->action;
+       tcf_action_set_ctrlact(*a, parm->action, newchain);
        rcu_swap_protected(p->params, params_new,
                           lockdep_is_held(&p->tcf_lock));
        spin_unlock_bh(&p->tcf_lock);
@@ -108,7 +116,13 @@ static int tcf_csum_init(struct net *net, struct nlattr 
*nla,
        if (ret == ACT_P_CREATED)
                tcf_idr_insert(tn, *a);
 
+end:
        return ret;
+error:
+       if (newchain)
+               tcf_chain_put_by_act(newchain);
+       tcf_idr_release(*a, bind);
+       goto end;
 }
 
 /**
-- 
2.20.1