Sun, Nov 19, 2017 at 12:44:05PM CET, c...@rkapl.cz wrote:
>If you flush (delete) a filter chain other than chain 0 (such as when
>deleting the device), the kernel may run into a use-after-free. The
>chain refcount must not be decremented unless we are sure we are done
>with the chain.
>
>To reproduce the bug, run:
> ip link add dtest type dummy
> tc qdisc add dev dtest ingress
> tc filter add dev dtest chain 1 parent ffff: flower
> ip link del dtest
>
>Introduced in: commit f93e1cdcf42c ("net/sched: fix filter flushing"),
>but unless you have KAsan or luck, you won't notice it until
>commit 0dadc117ac8b ("cls_flower: use tcf_exts_get_net() before call_rcu()")
Patch looks fine. Please repost with proper "Fixes: " tag.
Feel free to add my:
Acked-by: Jiri Pirko <j...@mellanox.com>
tag.
Thanks!
>
>Signed-off-by: Roman Kapl <c...@rkapl.cz>
>---
> net/sched/cls_api.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
>diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>index ab255b421781..7d97f612c9b9 100644
>--- a/net/sched/cls_api.c
>+++ b/net/sched/cls_api.c
>@@ -205,13 +205,14 @@ static void tcf_chain_head_change(struct tcf_chain
>*chain,
>
> static void tcf_chain_flush(struct tcf_chain *chain)
> {
>- struct tcf_proto *tp;
>+ struct tcf_proto *tp = rtnl_dereference(chain->filter_chain);
>
> tcf_chain_head_change(chain, NULL);
>- while ((tp = rtnl_dereference(chain->filter_chain)) != NULL) {
>+ while (tp) {
> RCU_INIT_POINTER(chain->filter_chain, tp->next);
>- tcf_chain_put(chain);
> tcf_proto_destroy(tp);
>+ tp = rtnl_dereference(chain->filter_chain);
>+ tcf_chain_put(chain);
> }
> }
>
>--
>2.15.0
>
