* [PATCH bpf-next v3 1/2] flow_dissector: Allow updating the flow dissector program atomically
2019-10-11 8:29 [PATCH bpf-next v3 0/2] Atomic flow dissector updates Jakub Sitnicki
@ 2019-10-11 8:29 ` Jakub Sitnicki
2019-10-11 8:29 ` [PATCH bpf-next v3 2/2] selftests/bpf: Check that flow dissector can be re-attached Jakub Sitnicki
2019-10-11 21:24 ` [PATCH bpf-next v3 0/2] Atomic flow dissector updates Daniel Borkmann
2 siblings, 0 replies; 4+ messages in thread
From: Jakub Sitnicki @ 2019-10-11 8:29 UTC (permalink / raw)
To: bpf; +Cc: netdev, kernel-team, Stanislav Fomichev, Martin KaFai Lau
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>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
---
net/core/flow_dissector.c | 10 +++++++---
1 file 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,
lockdep_is_held(&flow_dissector_mutex));
- 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);
out:
mutex_unlock(&flow_dissector_mutex);
return ret;
--
2.20.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH bpf-next v3 2/2] selftests/bpf: Check that flow dissector can be re-attached
2019-10-11 8:29 [PATCH bpf-next v3 0/2] Atomic flow dissector updates Jakub Sitnicki
2019-10-11 8:29 ` [PATCH bpf-next v3 1/2] flow_dissector: Allow updating the flow dissector program atomically Jakub Sitnicki
@ 2019-10-11 8:29 ` Jakub Sitnicki
2019-10-11 21:24 ` [PATCH bpf-next v3 0/2] Atomic flow dissector updates Daniel Borkmann
2 siblings, 0 replies; 4+ messages in thread
From: Jakub Sitnicki @ 2019-10-11 8:29 UTC (permalink / raw)
To: bpf; +Cc: netdev, kernel-team, Stanislav Fomichev, Martin KaFai Lau
Make sure a new flow dissector program can be attached to replace the old
one with a single syscall. Also check that attaching the same program twice
is prohibited.
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
---
.../bpf/prog_tests/flow_dissector_reattach.c | 127 ++++++++++++++++++
1 file changed, 127 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/flow_dissector_reattach.c
diff --git a/tools/testing/selftests/bpf/prog_tests/flow_dissector_reattach.c b/tools/testing/selftests/bpf/prog_tests/flow_dissector_reattach.c
new file mode 100644
index 000000000000..777faffc4639
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/flow_dissector_reattach.c
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test that the flow_dissector program can be updated with a single
+ * syscall by attaching a new program that replaces the existing one.
+ *
+ * Corner case - the same program cannot be attached twice.
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+#include <linux/bpf.h>
+#include <bpf/bpf.h>
+
+#include "test_progs.h"
+
+static bool is_attached(int netns)
+{
+ __u32 cnt;
+ int err;
+
+ err = bpf_prog_query(netns, BPF_FLOW_DISSECTOR, 0, NULL, NULL, &cnt);
+ if (CHECK_FAIL(err)) {
+ perror("bpf_prog_query");
+ return true; /* fail-safe */
+ }
+
+ return cnt > 0;
+}
+
+static int load_prog(void)
+{
+ struct bpf_insn prog[] = {
+ BPF_MOV64_IMM(BPF_REG_0, BPF_OK),
+ BPF_EXIT_INSN(),
+ };
+ int fd;
+
+ fd = bpf_load_program(BPF_PROG_TYPE_FLOW_DISSECTOR, prog,
+ ARRAY_SIZE(prog), "GPL", 0, NULL, 0);
+ if (CHECK_FAIL(fd < 0))
+ perror("bpf_load_program");
+
+ return fd;
+}
+
+static void do_flow_dissector_reattach(void)
+{
+ int prog_fd[2] = { -1, -1 };
+ int err;
+
+ prog_fd[0] = load_prog();
+ if (prog_fd[0] < 0)
+ return;
+
+ prog_fd[1] = load_prog();
+ if (prog_fd[1] < 0)
+ goto out_close;
+
+ err = bpf_prog_attach(prog_fd[0], 0, BPF_FLOW_DISSECTOR, 0);
+ if (CHECK_FAIL(err)) {
+ perror("bpf_prog_attach-0");
+ goto out_close;
+ }
+
+ /* Expect success when attaching a different program */
+ err = bpf_prog_attach(prog_fd[1], 0, BPF_FLOW_DISSECTOR, 0);
+ if (CHECK_FAIL(err)) {
+ perror("bpf_prog_attach-1");
+ goto out_detach;
+ }
+
+ /* Expect failure when attaching the same program twice */
+ err = bpf_prog_attach(prog_fd[1], 0, BPF_FLOW_DISSECTOR, 0);
+ if (CHECK_FAIL(!err || errno != EINVAL))
+ perror("bpf_prog_attach-2");
+
+out_detach:
+ err = bpf_prog_detach(0, BPF_FLOW_DISSECTOR);
+ if (CHECK_FAIL(err))
+ perror("bpf_prog_detach");
+
+out_close:
+ close(prog_fd[1]);
+ close(prog_fd[0]);
+}
+
+void test_flow_dissector_reattach(void)
+{
+ int init_net, err;
+
+ init_net = open("/proc/1/ns/net", O_RDONLY);
+ if (CHECK_FAIL(init_net < 0)) {
+ perror("open(/proc/1/ns/net)");
+ return;
+ }
+
+ err = setns(init_net, CLONE_NEWNET);
+ if (CHECK_FAIL(err)) {
+ perror("setns(/proc/1/ns/net)");
+ goto out_close;
+ }
+
+ if (is_attached(init_net)) {
+ test__skip();
+ printf("Can't test with flow dissector attached to init_net\n");
+ return;
+ }
+
+ /* First run tests in root network namespace */
+ do_flow_dissector_reattach();
+
+ /* Then repeat tests in a non-root namespace */
+ err = unshare(CLONE_NEWNET);
+ if (CHECK_FAIL(err)) {
+ perror("unshare(CLONE_NEWNET)");
+ goto out_close;
+ }
+ do_flow_dissector_reattach();
+
+out_close:
+ close(init_net);
+}
--
2.20.1
^ permalink raw reply related [flat|nested] 4+ messages in thread