Subject: Re: [Patch net] act_pedit: check binding before calling tcf_hash_release()

From: Daniel Borkmann <[email-masked]>
Date: Fri, 31 Jul 2015 13:10:35 +0200

On 07/31/2015 02:12 AM, Cong Wang wrote:
> When we share an action within a filter, the bind refcnt
> should increase, therefore we should not call tcf_hash_release().
>
> Cc: Jamal Hadi Salim <[email-masked]>
> Cc: Daniel Borkmann <[email-masked]>
> Signed-off-by: Cong Wang <[email-masked]>
> Signed-off-by: Cong Wang <[email-masked]>

Seems like this slipped in via commit 1a29321ed045. The ugly thing is that
this leads to a use-after-free.

# tc actions add action pedit munge offset 2 u16 at 0 0f0000000 22 set 11500
# tc actions show action pedit
   action order 0:  pedit action pass keys 1
   index 1 ref 1 bind 0
   key #0  at 0: val 00002cec mask ffff0000
# tc filter add dev foo parent 1: bpf bytecode "$FOO" flowid 1:1 action pedit index 1
# tc filter show dev foo
   filter parent 1: protocol all pref 49152 bpf
   filter parent 1: protocol all pref 49152 bpf handle 0x1 flowid 1:1 bytecode '1,6 0 0 4294967295'
   action order 1: pedit action pass keys 1
   index 1 ref 1 bind 0
   key #0  at 0: val 00002cec mask ffff0000
# tc actions del action pedit index 1

.... and now you can wait for the next egress packet. ;)

Thanks for the fix Cong!

Fixes: 1a29321ed045 ("net_sched: act: Dont increment refcnt on replace")
Acked-by: Daniel Borkmann <[email-masked]>