From: Jakub Sitnicki jakub@cloudflare.com
commit 5cf65922bb15279402e1e19b5ee8c51d618fa51f upstream.
When attaching a flow dissector program to a network namespace with bpf(BPF_PROG_ATTACH, ...) we grab a reference to bpf_prog.
If netns gets destroyed while a flow dissector is still attached, and there are no other references to the prog, we leak the reference and the program remains loaded.
Leak can be reproduced by running flow dissector tests from selftests/bpf:
# bpftool prog list # ./test_flow_dissector.sh ... selftests: test_flow_dissector [PASS] # bpftool prog list 4: flow_dissector name _dissect tag e314084d332a5338 gpl loaded_at 2020-05-20T18:50:53+0200 uid 0 xlated 552B jited 355B memlock 4096B map_ids 3,4 btf_id 4 #
Fix it by detaching the flow dissector program when netns is going away.
Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook") Signed-off-by: Jakub Sitnicki jakub@cloudflare.com Signed-off-by: Alexei Starovoitov ast@kernel.org Reviewed-by: Stanislav Fomichev sdf@google.com Link: https://lore.kernel.org/bpf/20200521083435.560256-1-jakub@cloudflare.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/core/flow_dissector.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)
--- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -160,12 +160,10 @@ out: return ret; }
-int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr) +static int flow_dissector_bpf_prog_detach(struct net *net) { struct bpf_prog *attached; - struct net *net;
- net = current->nsproxy->net_ns; mutex_lock(&flow_dissector_mutex); attached = rcu_dereference_protected(net->flow_dissector_prog, lockdep_is_held(&flow_dissector_mutex)); @@ -179,6 +177,24 @@ int skb_flow_dissector_bpf_prog_detach(c return 0; }
+int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr) +{ + return flow_dissector_bpf_prog_detach(current->nsproxy->net_ns); +} + +static void __net_exit flow_dissector_pernet_pre_exit(struct net *net) +{ + /* We're not racing with attach/detach because there are no + * references to netns left when pre_exit gets called. + */ + if (rcu_access_pointer(net->flow_dissector_prog)) + flow_dissector_bpf_prog_detach(net); +} + +static struct pernet_operations flow_dissector_pernet_ops __net_initdata = { + .pre_exit = flow_dissector_pernet_pre_exit, +}; + /** * __skb_flow_get_ports - extract the upper layer ports and return them * @skb: sk_buff to extract the ports from @@ -1838,7 +1854,7 @@ static int __init init_default_flow_diss skb_flow_dissector_init(&flow_keys_basic_dissector, flow_keys_basic_dissector_keys, ARRAY_SIZE(flow_keys_basic_dissector_keys)); - return 0; -}
+ return register_pernet_subsys(&flow_dissector_pernet_ops); +} core_initcall(init_default_flow_dissectors);