The following test case causes a NULL pointer dereference in cls_bpf:

  FOO="1,6 0 0 4294967295,"
  tc filter add dev foo parent 1: bpf bytecode "$FOO" flowid 1:1 action ok
  tc filter replace dev foo parent 1: pref 49152 handle 0x1 \
            bpf bytecode "$FOO" flowid 1:1 action drop

The problem is that commit 1f947bf151e9 ("net: sched: rcu'ify cls_bpf")
accidentally swapped the arguments of list_replace_rcu(), the old
element needs to be the first argument and the new element the second.

Fixes: 1f947bf151e9 ("net: sched: rcu'ify cls_bpf")
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
---
 net/sched/cls_bpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index c79ecfd..e5168f8 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -378,7 +378,7 @@ static int cls_bpf_change(struct net *net, struct sk_buff 
*in_skb,
                goto errout;
 
        if (oldprog) {
-               list_replace_rcu(&prog->link, &oldprog->link);
+               list_replace_rcu(&oldprog->link, &prog->link);
                tcf_unbind_filter(tp, &oldprog->res);
                call_rcu(&oldprog->rcu, __cls_bpf_delete_prog);
        } else {
-- 
1.9.3

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