Subject: Re: [PATCH net-next 00/11] net: sched: cls_u32 Various improvements

From: Al Viro <[email-masked]>
Date: Mon, 8 Oct 2018 06:45:15 +0100

On Sun, Oct 07, 2018 at 09:25:01PM -0700, David Miller wrote:
> From: Jamal Hadi Salim <[email-masked]>
> Date: Sun,  7 Oct 2018 12:38:00 -0400
> 
> > Various improvements from Al.
> 
> Please submit changes that actually are compile tested:
> 
>   CC [M]  net/sched/cls_u32.o
> net/sched/cls_u32.c: In function ‘u32_delete’:
> net/sched/cls_u32.c:674:6: error: ‘root_ht’ undeclared (first use in this function); did you mean ‘root_user’?
>   if (root_ht == ht) {
>       ^~~~~~~
>       root_user
> net/sched/cls_u32.c:674:6: note: each undeclared identifier is reported only once for each function it appears in
> net/sched/cls_u32.c: In function ‘u32_set_parms’:
> net/sched/cls_u32.c:746:15: error: ‘struct tc_u_hnode’ has no member named ‘is_root’
>     if (ht_down->is_root) {
>                ^~

Er...  Both are due to missing in the very beginning of the series (well, on
top of "net: sched: cls_u32: fix hnode refcounting") commit

Author: Al Viro <[email-masked]>
Date:   Mon Sep 3 14:39:02 2018 -0400

    net: sched: cls_u32: mark root hnode explicitly
    
    ... and produce consistent error on attempt to delete such.
    Existing check in u32_delete() is inconsistent - after
    
    tc qdisc add dev eth0 ingress
    tc filter add dev eth0 parent ffff: protocol ip prio 100 handle 1: u32 divisor 1
    tc filter add dev eth0 parent ffff: protocol ip prio 200 handle 2: u32 divisor 1
    
    both
    
    tc filter delete dev eth0 parent ffff: protocol ip prio 100 handle 801: u32
    
    and
    
    tc filter delete dev eth0 parent ffff: protocol ip prio 100 handle 800: u32
    
    will fail (at least with refcounting fixes), but the former will complain
    about an attempt to remove a busy table, while the latter will recognize
    it as root and yield "Not allowed to delete root node" instead.
    
    The problem with the existing check is that several tcf_proto instances might
    share the same tp->data and handle-to-hnode lookup will be the same for all
    of them.  So comparing an hnode to be deleted with tp->root won't catch the
    case when one tp is used to try deleting the root of another.  Solution is
    trivial - mark the root hnodes explicitly upon allocation and check for that.
    
    Signed-off-by: Al Viro <[email-masked]>

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index b2c3406a2cf2..c4782aa808c7 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;
 	}