Re: [PATCH bpf-next 2/3] selftests/bpf: add tests for TCP_BPF_SOCK_OPS_CB_FLAGS

Martin KaFai Lau <martin.lau@xxxxxxxxx> · Wed, 7 Aug 2024 14:14:17 -0700

On 8/7/24 10:58 AM, Alan Maguire wrote:
On 06/08/2024 22:27, Martin KaFai Lau wrote:
On 8/2/24 8:29 AM, Alan Maguire wrote:
Add tests to set/get TCP sockopt TCP_BPF_SOCK_OPS_CB_FLAGS via
bpf_setsockopt() and also add a cgroup/setsockopt program that
catches setsockopt() for this option and uses bpf_setsockopt()
to set it.  The latter allows us to support modifying sockops
cb flags on a per-socket basis via setsockopt() without adding
support into core setsockopt() itself.

Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
   .../selftests/bpf/prog_tests/setget_sockopt.c | 11 ++++++
   .../selftests/bpf/progs/setget_sockopt.c      | 37 +++++++++++++++++--
   2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/setget_sockopt.c
b/tools/testing/selftests/bpf/prog_tests/setget_sockopt.c
index 7d4a9b3d3722..b9c54217a489 100644
--- a/tools/testing/selftests/bpf/prog_tests/setget_sockopt.c
+++ b/tools/testing/selftests/bpf/prog_tests/setget_sockopt.c
@@ -42,6 +42,7 @@ static int create_netns(void)
   static void test_tcp(int family)
   {
       struct setget_sockopt__bss *bss = skel->bss;
+    int cb_flags = BPF_SOCK_OPS_STATE_CB_FLAG |
BPF_SOCK_OPS_RTO_CB_FLAG;
       int sfd, cfd;
         memset(bss, 0, sizeof(*bss));
@@ -56,6 +57,9 @@ static void test_tcp(int family)
           close(sfd);
           return;
       }
+    ASSERT_EQ(setsockopt(sfd, SOL_TCP, TCP_BPF_SOCK_OPS_CB_FLAGS,
+                 &cb_flags, sizeof(cb_flags)),
+          0, "setsockopt cb_flags");

The sfd here is the listen fd. The setsockopt here is after the
connection is established and the connection won't be affected by this
setsockopt...

I don't think this test belongs to test_tcp() here, more on this below...

       close(sfd);
       close(cfd);
   @@ -65,6 +69,8 @@ static void test_tcp(int family)
       ASSERT_EQ(bss->nr_passive, 1, "nr_passive");
       ASSERT_EQ(bss->nr_socket_post_create, 2, "nr_socket_post_create");
       ASSERT_EQ(bss->nr_binddev, 2, "nr_bind");
+    ASSERT_GE(bss->nr_state, 1, "nr_state");
+    ASSERT_EQ(bss->nr_setsockopt, 1, "nr_setsockopt");
   }
     static void test_udp(int family)
@@ -185,6 +191,11 @@ void test_setget_sockopt(void)
       if (!ASSERT_OK_PTR(skel->links.socket_post_create,
"attach_cgroup"))
           goto done;
   +    skel->links.tcp_setsockopt =
+        bpf_program__attach_cgroup(skel->progs.tcp_setsockopt, cg_fd);
+    if (!ASSERT_OK_PTR(skel->links.tcp_setsockopt, "attach_setsockopt"))
+        goto done;
+
       test_tcp(AF_INET6);
       test_tcp(AF_INET);
       test_udp(AF_INET6);
diff --git a/tools/testing/selftests/bpf/progs/setget_sockopt.c
b/tools/testing/selftests/bpf/progs/setget_sockopt.c
index 60518aed1ffc..920af9e21e84 100644
--- a/tools/testing/selftests/bpf/progs/setget_sockopt.c
+++ b/tools/testing/selftests/bpf/progs/setget_sockopt.c
@@ -20,6 +20,8 @@ int nr_connect;
   int nr_binddev;
   int nr_socket_post_create;
   int nr_fin_wait1;
+int nr_state;
+int nr_setsockopt;
     struct sockopt_test {
       int opt;
@@ -59,6 +61,8 @@ static const struct sockopt_test sol_tcp_tests[] = {
       { .opt = TCP_THIN_LINEAR_TIMEOUTS, .flip = 1, },
       { .opt = TCP_USER_TIMEOUT, .new = 123400, .expected = 123400, },
       { .opt = TCP_NOTSENT_LOWAT, .new = 1314, .expected = 1314, },
+    { .opt = TCP_BPF_SOCK_OPS_CB_FLAGS, .new =
BPF_SOCK_OPS_ALL_CB_FLAGS,
+      .expected = BPF_SOCK_OPS_ALL_CB_FLAGS, .restore =
BPF_SOCK_OPS_STATE_CB_FLAG, },
       { .opt = 0, },
   };
   @@ -124,6 +128,7 @@ static int bpf_test_sockopt_int(void *ctx,
struct sock *sk,
         if (bpf_setsockopt(ctx, level, opt, &new, sizeof(new)))
           return 1;
+
       if (bpf_getsockopt(ctx, level, opt, &tmp, sizeof(tmp)) ||
           tmp != expected)
           return 1;
@@ -384,11 +389,14 @@ int skops_sockopt(struct bpf_sock_ops *skops)
           nr_passive += !(bpf_test_sockopt(skops, sk) ||
                   test_tcp_maxseg(skops, sk) ||
                   test_tcp_saved_syn(skops, sk));
-        bpf_sock_ops_cb_flags_set(skops,
-                      skops->bpf_sock_ops_cb_flags |
-                      BPF_SOCK_OPS_STATE_CB_FLAG);
+
+        /* no need to set sockops cb flags here as sockopt
+         * tests and user-space originated setsockopt() will
+         * set flags to include BPF_SOCK_OPS_STATE_CB.
+         */

I don't think the "user-space originated..." comment is accruate here.
The user-space originated setsockopt() from the above test_tcp() won't
affect the passively established sk here. This took me a while to digest...

iiuc, the removed bpf_sock_ops_cb_flags_set() for the passive connection
is now implicitly done (and hidden) in the newly added
sol_tcp_tests[].restore.

How about keeping the explicit bpf_sock_ops_cb_flags_set() and removing
the ".restore".

The existing bpf_sock_ops_cb_flags_set() can be changed to
bpf_setsockopt(TCP_BPF_SOCK_OPS_CB_FLAGS) if it helps to test if it is
effective.

Sounds good; I'll make that change and avoid changing test_tcp() etc.

           break;
       case BPF_SOCK_OPS_STATE_CB:
+        nr_state++;

How about removing the nr_state addition and adding a
SEC("cgroup/getsockopt") bpf prog to test the
getsockopt(TCP_BPF_SOCK_OPS_CB_FLAGS).


Will do. Given that currently we cannot call bpf_getsockopt() from
cgroup/getsockopt progs it might make sense to use per-socket storage to
store the cb flags value that we set via bpf_setsockopt() in the sock
ops program, and retrieve it in the cgroup/getsockopt prog. Does that
sound ok?

The bpf_sock_ops_cb_flags can be directly inspected in cgroup/getsockopt
with the help of bpf_core_cast(). The following is based on the patch3's
_getsockopt (untested):

#include <vmlinux.h>
#include <bpf/bpf_core_read.h>

SEC("cgroup/getsockopt")
int _getsockopt(struct bpf_sockopt *ctx)
{
	struct bpf_sock *sk = ctx->sk;
	int *optval = ctx->optval;
	struct tcp_sock *tp;

	if (!sk || ctx->level != SOL_TCP || ctx->optname != TCP_BPF_SOCK_OPS_CB_FLAGS || sk->protocol != IPPROTO_TCP ||
	    ctx->optval + sizeof(int) > ctx->optval_end)
		return 1;

	tp = bpf_core_cast(sk, struct tcp_sock);
	*optval = tp->bpf_sock_ops_cb_flags;
	ctx->retval = 0;
	return 1;
}








