Re: [patch net] net: sched: fix use-after-free in tcf_action_destroy and tcf_del_walker

Wed, Sep 13, 2017 at 06:34:28PM CEST, davem@davemloft.net wrote:

From: Jiri Pirko <jiri@resnulli.us>
Date: Wed, 13 Sep 2017 17:32:37 +0200

quoted

From: Jiri Pirko <redacted>

Recent commit d7fb60b9cafb ("net_sched: get rid of tcfa_rcu") removed
freeing in call_rcu, which changed already existing hard-to-hit
race condition into 100% hit:

[  598.599825] BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
[  598.607782] IP: tcf_action_destroy+0xc0/0x140

Or:

[   40.858924] BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
[   40.862840] IP: tcf_generic_walker+0x534/0x820

Fix this by storing the ops and use them directly for module_put call.

Fixes: a85a970af265 ("net_sched: move tc_action into tcf_common")
Signed-off-by: Jiri Pirko <redacted>

Applied, thanks Jiri.

Oh, I forgot to mention, this would be nice to push to stable.