[PATCH bpf-next v3 1/2] bpf: use proper target btf when exporting attach_btf_obj_id

[PATCH bpf-next v3 1/2] bpf: use proper target btf when exporting attach_btf_obj_id

[Stanislav Fomichev]

When attaching to program, the program itself might not be attached
to anything (and, hence, might not have attach_btf), so we can't
unconditionally use 'prog->aux->dst_prog->aux->attach_btf'.
Instead, use bpf_prog_get_target_btf to pick proper target btf:

* when attached to dst_prog, use dst_prog->aux->btf
* when attached to kernel btf, use prog->aux->attach_btf

Fixes: b79c9fc9551b ("bpf: implement BPF_PROG_QUERY for BPF_LSM_CGROUP")
Acked-by: Hao Luo <haoluo@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 kernel/bpf/syscall.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 83c7136c5788..7dc3f8003631 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3886,6 +3886,7 @@ static int bpf_prog_get_info_by_fd(struct file *file,
 				   union bpf_attr __user *uattr)
 {
 	struct bpf_prog_info __user *uinfo = u64_to_user_ptr(attr->info.info);
+	struct btf *attach_btf = bpf_prog_get_target_btf(prog);
 	struct bpf_prog_info info;
 	u32 info_len = attr->info.info_len;
 	struct bpf_prog_kstats stats;
@@ -4088,10 +4089,8 @@ static int bpf_prog_get_info_by_fd(struct file *file,
 	if (prog->aux->btf)
 		info.btf_id = btf_obj_id(prog->aux->btf);
 	info.attach_btf_id = prog->aux->attach_btf_id;
-	if (prog->aux->attach_btf)
-		info.attach_btf_obj_id = btf_obj_id(prog->aux->attach_btf);
-	else if (prog->aux->dst_prog)
-		info.attach_btf_obj_id = btf_obj_id(prog->aux->dst_prog->aux->attach_btf);
+	if (attach_btf)
+		info.attach_btf_obj_id = btf_obj_id(attach_btf);
 
 	ulen = info.nr_func_info;
 	info.nr_func_info = prog->aux->func_info_cnt;
-- 
2.37.1.559.g78731f0fdb-goog

[PATCH bpf-next v3 2/2] selftests/bpf: Excercise bpf_obj_get_info_by_fd for bpf2bpf

[Stanislav Fomichev]

Apparently, no existing selftest covers it. Add a new one where
we load cgroup/bind4 program and attach fentry to it.
Calling bpf_obj_get_info_by_fd on the fentry program
should return non-zero btf_id/btf_obj_id instead of crashing the kernel.

v3:
- move into fexit_bpf2bpf.c (Martin)
- assert on skel->links.bind_v4_prog (Andrii)
- do no close(-1) unconditionally (Andrii)

v2:
- use ret instead of err in find_prog_btf_id (Hao)
- remove verifier log (Hao)
- drop if conditional from ASSERT_OK(bpf_obj_get_info_by_fd(...)) (Hao)

Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  | 95 +++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
index 02bb8cbf9194..da860b07abb5 100644
--- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
@@ -3,6 +3,7 @@
 #include <test_progs.h>
 #include <network_helpers.h>
 #include <bpf/btf.h>
+#include "bind4_prog.skel.h"
 
 typedef int (*test_cb)(struct bpf_object *obj);
 
@@ -407,6 +408,98 @@ static void test_func_replace_global_func(void)
 				  prog_name, false, NULL);
 }
 
+static int find_prog_btf_id(const char *name, __u32 attach_prog_fd)
+{
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
+	struct btf *btf;
+	int ret;
+
+	ret = bpf_obj_get_info_by_fd(attach_prog_fd, &info, &info_len);
+	if (ret)
+		return ret;
+
+	if (!info.btf_id)
+		return -EINVAL;
+
+	btf = btf__load_from_kernel_by_id(info.btf_id);
+	ret = libbpf_get_error(btf);
+	if (ret)
+		return ret;
+
+	ret = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
+	btf__free(btf);
+	return ret;
+}
+
+static int load_fentry(int attach_prog_fd, int attach_btf_id)
+{
+	LIBBPF_OPTS(bpf_prog_load_opts, opts,
+		    .expected_attach_type = BPF_TRACE_FENTRY,
+		    .attach_prog_fd = attach_prog_fd,
+		    .attach_btf_id = attach_btf_id,
+	);
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+
+	return bpf_prog_load(BPF_PROG_TYPE_TRACING,
+			     "bind4_fentry",
+			     "GPL",
+			     insns,
+			     ARRAY_SIZE(insns),
+			     &opts);
+}
+
+static void test_fentry_to_cgroup_bpf(void)
+{
+	struct bind4_prog *skel = NULL;
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
+	int cgroup_fd = -1;
+	int fentry_fd = -1;
+	int btf_id;
+
+	cgroup_fd = test__join_cgroup("/fentry_to_cgroup_bpf");
+	if (!ASSERT_GE(cgroup_fd, 0, "cgroup_fd"))
+		return;
+
+	skel = bind4_prog__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		goto cleanup;
+
+	skel->links.bind_v4_prog = bpf_program__attach_cgroup(skel->progs.bind_v4_prog, cgroup_fd);
+	if (!ASSERT_OK_PTR(skel->links.bind_v4_prog, "bpf_program__attach_cgroup"))
+		goto cleanup;
+
+	btf_id = find_prog_btf_id("bind_v4_prog", bpf_program__fd(skel->progs.bind_v4_prog));
+	if (!ASSERT_GE(btf_id, 0, "find_prog_btf_id"))
+		goto cleanup;
+
+	fentry_fd = load_fentry(bpf_program__fd(skel->progs.bind_v4_prog), btf_id);
+	if (!ASSERT_GE(fentry_fd, 0, "load_fentry"))
+		goto cleanup;
+
+	/* Make sure bpf_obj_get_info_by_fd works correctly when attaching
+	 * to another BPF program.
+	 */
+
+	ASSERT_OK(bpf_obj_get_info_by_fd(fentry_fd, &info, &info_len),
+		  "bpf_obj_get_info_by_fd");
+
+	ASSERT_EQ(info.btf_id, 0, "info.btf_id");
+	ASSERT_EQ(info.attach_btf_id, btf_id, "info.attach_btf_id");
+	ASSERT_GT(info.attach_btf_obj_id, 0, "info.attach_btf_obj_id");
+
+cleanup:
+	if (cgroup_fd >= 0)
+		close(cgroup_fd);
+	if (fentry_fd >= 0)
+		close(fentry_fd);
+	bind4_prog__destroy(skel);
+}
+
 /* NOTE: affect other tests, must run in serial mode */
 void serial_test_fexit_bpf2bpf(void)
 {
@@ -430,4 +523,6 @@ void serial_test_fexit_bpf2bpf(void)
 		test_fmod_ret_freplace();
 	if (test__start_subtest("func_replace_global_func"))
 		test_func_replace_global_func();
+	if (test__start_subtest("fentry_to_cgroup_bpf"))
+		test_fentry_to_cgroup_bpf();
 }
-- 
2.37.1.559.g78731f0fdb-goog

Re: [PATCH bpf-next v3 1/2] bpf: use proper target btf when exporting attach_btf_obj_id

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Thu,  4 Aug 2022 13:11:39 -0700 you wrote:
> When attaching to program, the program itself might not be attached
> to anything (and, hence, might not have attach_btf), so we can't
> unconditionally use 'prog->aux->dst_prog->aux->attach_btf'.
> Instead, use bpf_prog_get_target_btf to pick proper target btf:
> 
> * when attached to dst_prog, use dst_prog->aux->btf
> * when attached to kernel btf, use prog->aux->attach_btf
> 
> [...]

Here is the summary with links:
  - [bpf-next,v3,1/2] bpf: use proper target btf when exporting attach_btf_obj_id
    https://git.kernel.org/bpf/bpf/c/6644aabbd897
  - [bpf-next,v3,2/2] selftests/bpf: Excercise bpf_obj_get_info_by_fd for bpf2bpf
    https://git.kernel.org/bpf/bpf/c/ffd5cfca5388

You are awesome, thank you!
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