Re: [PATCH 2/7] mark root hnode explicitly

[Al Viro]

On Thu, Sep 06, 2018 at 06:34:00AM -0400, Jamal Hadi Salim wrote:
> On 2018-09-06 6:28 a.m., Jamal Hadi Salim wrote:
> > On 2018-09-05 3:04 p.m., Al Viro wrote:
> > > From: Al Viro <v...@zeniv.linux.org.uk>
> > > 
> > > ... and disallow deleting or linking to such
> > > 
> > > Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
> > 
> > Same comment as other one in regards to subject
> > 
> > Since the flag space is coming from htnode which is
> > exposed via uapi it makes sense to keep this one here
> > because it is for private use; but  a comment in
> > include/uapi/linux/pkt_cls.h that this flag or
> > maybe a set of bits is reserved for internal use.
> > Otherwise:
> > 
> > Acked-by: Jamal Hadi Salim <j...@mojatatu.com>
> 
> 
> Sorry, additional comment:
> It makes sense to reject user space attempt to
> set TCA_CLS_FLAGS_U32_ROOT

Point, and that one is IMO enough to give up on using ->flags for
that.  How about simply

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 3f985f29ef30..d14048e38b5c 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -84,6 +84,7 @@ struct tc_u_hnode {
        int                     refcnt;
        unsigned int            divisor;
        struct idr              handle_idr;
+       bool                    is_root;
        struct rcu_head         rcu;
        u32                     flags;
        /* The 'ht' field MUST be the last field in structure to allow for
@@ -377,6 +378,7 @@ static int u32_init(struct tcf_proto *tp)
        root_ht->refcnt++;
        root_ht->handle = tp_c ? gen_new_htid(tp_c, root_ht) : 0x80000000;
        root_ht->prio = tp->prio;
+       root_ht->is_root = true;
        idr_init(&root_ht->handle_idr);
 
        if (tp_c == NULL) {
@@ -693,7 +695,7 @@ static int u32_delete(struct tcf_proto *tp, void *arg, bool 
*last,
                goto out;
        }
 
-       if (root_ht == ht) {
+       if (ht->is_root) {
                NL_SET_ERR_MSG_MOD(extack, "Not allowed to delete root node");
                return -EINVAL;
        }
@@ -795,6 +797,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto 
*tp,
                                NL_SET_ERR_MSG_MOD(extack, "Link hash table not 
found");
                                return -EINVAL;
                        }
+                       if (ht_down->is_root) {
+                               NL_SET_ERR_MSG_MOD(extack, "Not linking to root 
node");
+                               return -EINVAL;
+                       }
                        ht_down->refcnt++;
                }