path: root/net/core/flow_dissector.c
diff options
authorJakub Sitnicki <jakub@cloudflare.com>2019-10-11 10:29:45 +0200
committerDaniel Borkmann <daniel@iogearbox.net>2019-10-11 22:26:22 +0200
commit719b78a5674f15fef2e4a56484614657fd759978 (patch)
tree6dfbc486cd94db2fc45a75ad11d94b26d1c806ae /net/core/flow_dissector.c
parentbpf: Align struct bpf_prog_stats (diff)
flow_dissector: Allow updating the flow dissector program atomically
It is currently not possible to detach the flow dissector program and attach a new one in an atomic fashion, that is with a single syscall. Attempts to do so will be met with EEXIST error. This makes updates to flow dissector program hard. Traffic steering that relies on BPF-powered flow dissection gets disrupted while old program has been already detached but the new one has not been attached yet. There is also a window of opportunity to attach a flow dissector to a non-root namespace while updating the root flow dissector, thus blocking the update. Lastly, the behavior is inconsistent with cgroup BPF programs, which can be replaced with a single bpf(BPF_PROG_ATTACH, ...) syscall without any restrictions. Allow attaching a new flow dissector program when another one is already present with a restriction that it can't be the same program. Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Stanislav Fomichev <sdf@google.com> Acked-by: Martin KaFai Lau <kafai@fb.com> Link: https://lore.kernel.org/bpf/20191011082946.22695-2-jakub@cloudflare.com
Diffstat (limited to 'net/core/flow_dissector.c')
1 files changed, 7 insertions, 3 deletions
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 6b4b88d1599d..dbf502c18656 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -128,6 +128,8 @@ int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
struct net *ns;
for_each_net(ns) {
+ if (ns == &init_net)
+ continue;
if (rcu_access_pointer(ns->flow_dissector_prog)) {
ret = -EEXIST;
goto out;
@@ -145,12 +147,14 @@ int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
attached = rcu_dereference_protected(net->flow_dissector_prog,
- if (attached) {
- /* Only one BPF program can be attached at a time */
- ret = -EEXIST;
+ if (attached == prog) {
+ /* The same program cannot be attached twice */
+ ret = -EINVAL;
goto out;
rcu_assign_pointer(net->flow_dissector_prog, prog);
+ if (attached)
+ bpf_prog_put(attached);
return ret;