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Date:   Wed, 25 Sep 2019 16:07:09 +0000
From:   Yonghong Song <yhs@...com>
To:     Carlos Neira <cneirabustos@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v11 4/4] tools/testing/selftests/bpf: Add
 self-tests for new helper.



On 9/24/19 8:20 AM, Carlos Neira wrote:
> Self tests added for new helper
> 
> Signed-off-by: Carlos Neira <cneirabustos@...il.com>
> ---
>   tools/testing/selftests/bpf/Makefile          |   2 +-
>   tools/testing/selftests/bpf/bpf_helpers.h     |   3 +
>   .../selftests/bpf/progs/test_pidns_kern.c     |  71 ++++++++
>   tools/testing/selftests/bpf/test_pidns.c      | 152 ++++++++++++++++++
>   4 files changed, 227 insertions(+), 1 deletion(-)
>   create mode 100644 tools/testing/selftests/bpf/progs/test_pidns_kern.c
>   create mode 100644 tools/testing/selftests/bpf/test_pidns.c
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 7f3196af1ae4..d86b28aa8f44 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -28,7 +28,7 @@ TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test
>   	test_sock test_btf test_sockmap get_cgroup_id_user test_socket_cookie \
>   	test_cgroup_storage test_select_reuseport test_section_names \
>   	test_netcnt test_tcpnotify_user test_sock_fields test_sysctl test_hashmap \
> -	test_btf_dump test_cgroup_attach xdping
> +	test_btf_dump test_cgroup_attach xdping test_pidns

Could you fold test_pidns into test_progs?

>   
>   BPF_OBJ_FILES = $(patsubst %.c,%.o, $(notdir $(wildcard progs/*.c)))
>   TEST_GEN_FILES = $(BPF_OBJ_FILES)
> diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
> index 6c4930bc6e2e..03d0e15ae29f 100644
> --- a/tools/testing/selftests/bpf/bpf_helpers.h
> +++ b/tools/testing/selftests/bpf/bpf_helpers.h
> @@ -231,6 +231,9 @@ static int (*bpf_send_signal)(unsigned sig) = (void *)BPF_FUNC_send_signal;
>   static long long (*bpf_tcp_gen_syncookie)(struct bpf_sock *sk, void *ip,
>   					  int ip_len, void *tcp, int tcp_len) =
>   	(void *) BPF_FUNC_tcp_gen_syncookie;
> +static int (*bpf_get_ns_current_pid_tgid)(__u32 dev, __u64 inum) =
> +	(void *) BPF_FUNC_get_ns_current_pid_tgid;
> +
>   
>   /* llvm builtin functions that eBPF C program may use to
>    * emit BPF_LD_ABS and BPF_LD_IND instructions
> diff --git a/tools/testing/selftests/bpf/progs/test_pidns_kern.c b/tools/testing/selftests/bpf/progs/test_pidns_kern.c
> new file mode 100644
> index 000000000000..96cb707db3ee
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_pidns_kern.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2018 Carlos Neira cneirabustos@...il.com

2019

> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of version 2 of the GNU General Public
> + * License as published by the Free Software Foundation.

You do not need the above statement, which is covered by
"SPDX-License-Identifier: GPL-2.0".

> + */
> +
> +#include <linux/bpf.h>
> +#include "bpf_helpers.h"
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__uint(max_entries, 1);
> +	__type(key, __u32);
> +	__type(value, __u64);
> +} ns_inum_map SEC(".maps");
> +
> +struct  {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__uint(max_entries, 1);
> +	__type(key, __u32);
> +	__type(value, __u32);
> +} ns_dev_map SEC(".maps");
> +
> +struct   {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__uint(max_entries, 1);
> +	__type(key, __u32);
> +	__type(value, __u32);
> +} pidmap SEC(".maps");

Can we make the value __u64 to include
both pid and tid to compare both?

> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__uint(max_entries, 1);
> +	__type(key, __u32);
> +	__type(value, __u64);
> +} ns_pid_map SEC(".maps");
> +
> 

The above four one-element maps are perfectly examples
to use static global variables which are supported
by the kernel.

You can take a look at the patch
   https://patchwork.ozlabs.org/patch/1081014/
which shows how user space can modify the map
values. In the future, we could have a better
interface to read/update those static variable
values.

> +
> +SEC("tracepoint/syscalls/sys_enter_nanosleep")
> +int trace(void *ctx)
> +{
> +	__u32 key = 0, *expected_pid, *dev;

expected_pid => __u64 *?

> +	__u64 *val, *inum, nspid;
> +	__u32 pid;
> +
> +	dev = bpf_map_lookup_elem(&ns_dev_map, &key);
> +	if (!dev)
> +		return 0;
> +
> +	inum = bpf_map_lookup_elem(&ns_inum_map, &key);
> +	if (!inum)
> +		return 0;
> +
> +	nspid = bpf_get_ns_current_pid_tgid(*dev, *inum);
> +	expected_pid = bpf_map_lookup_elem(&pidmap, &key);
> +
> +	if (!expected_pid || *expected_pid != nspid)
> +		return 0;
> +
> +	val = bpf_map_lookup_elem(&ns_pid_map, &key);
> +	if (val)
> +		*val = nspid;
> +
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> +__u32 _version SEC("version") = 1;
> diff --git a/tools/testing/selftests/bpf/test_pidns.c b/tools/testing/selftests/bpf/test_pidns.c
> new file mode 100644
> index 000000000000..088f8025f2bf
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/test_pidns.c
> @@ -0,0 +1,152 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2018 Carlos Neira cneirabustos@...il.com

2019

> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of version 2 of the GNU General Public
> + * License as published by the Free Software Foundation.

ditto. you do not need the above statement.

> + */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <syscall.h>
> +#include <unistd.h>
> +#include <linux/perf_event.h>
> +#include <sys/ioctl.h>
> +#include <sys/time.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf.h>
> +#include <bpf/libbpf.h>
> +
> +#include "cgroup_helpers.h"
> +#include "bpf_rlimit.h"
> +
> +#define CHECK(condition, tag, format...) ({		\
> +	int __ret = !!(condition);			\
> +	if (__ret) {					\
> +		printf("%s:FAIL:%s ", __func__, tag);	\
> +		printf(format);				\
> +	} else {					\
> +		printf("%s:PASS:%s\n", __func__, tag);	\
> +	}						\
> +	__ret;						\
> +})
> +
> +static int bpf_find_map(const char *test, struct bpf_object *obj,
> +			const char *name)
> +{
> +	struct bpf_map *map;
> +
> +	map = bpf_object__find_map_by_name(obj, name);
> +	if (!map)
> +		return -1;
> +	return bpf_map__fd(map);

The 'test' argument is not used here.
Also, we have bpf_object__find_map_fd_by_name() API, you can
use it and you do not need this function.

> +}
> +
> +
> +int main(int argc, char **argv)
> +{
> +	int pidmap_fd, ns_inum_map_fd, ns_dev_map_fd, ns_pid_map_fd;
> +	const char *probe_name = "syscalls/sys_enter_nanosleep";
> +	const char *file = "test_pidns_kern.o";
> +	int err, bytes, efd, prog_fd, pmu_fd;
> +	struct perf_event_attr attr = {};
> +	struct bpf_object *obj;
> +	__u32 nspid = 0;
> +	__u32 key = 0, pid;
> +	int exit_code = 1;

to make it reverse Christmas tree style?

> +	struct stat st;
> +	char buf[256];
> +
> +	err = bpf_prog_load(file, BPF_PROG_TYPE_TRACEPOINT, &obj, &prog_fd);
> +	if (CHECK(err, "bpf_prog_load", "err %d errno %d\n", err, errno))
> +		goto cleanup_cgroup_env;
> +
> +	ns_dev_map_fd = bpf_find_map(__func__, obj, "ns_dev_map");
> +	if (CHECK(ns_dev_map_fd < 0, "bpf_find_map", "err %d errno %d\n",
> +		  ns_dev_map_fd, errno))
> +		goto close_prog;
> +
> +	ns_inum_map_fd = bpf_find_map(__func__, obj, "ns_inum_map");
> +	if (CHECK(ns_inum_map_fd < 0, "bpf_find_map", "err %d errno %d\n",
> +		  ns_inum_map_fd, errno))
> +		goto close_prog;
> +
> +	ns_pid_map_fd = bpf_find_map(__func__, obj, "ns_pid_map");
> +	if (CHECK(ns_pid_map_fd < 0, "bpf_find_map", "err %d errno %d\n",
> +		  ns_pid_map_fd, errno))
> +		goto close_prog;
> +
> +	pidmap_fd = bpf_find_map(__func__, obj, "pidmap");
> +	if (CHECK(pidmap_fd < 0, "bpf_find_map", "err %d errno %d\n",
> +		  pidmap_fd, errno))
> +		goto close_prog;
> +
> +	pid = getpid();
> +	bpf_map_update_elem(pidmap_fd, &key, &pid, 0);

maybe
	id = (__u64) getpid() << 32 | gettid();
	bpf_map_update_elem(pidmap_fd, &key, &id, 0);

In your original above kernel code, you actually compare user space pid
to kernel tid, which is okay for this program as it is the main thread 
and tid == pid, but the mechanism is wrong.

> +
> +	if (stat("/proc/self/ns/pid", &st))
> +		goto close_prog;
> +
> +	bpf_map_update_elem(ns_inum_map_fd, &key, &st.st_ino, 0);
> +	bpf_map_update_elem(ns_dev_map_fd, &key, &st.st_dev, 0);
> +
> +
> +	snprintf(buf, sizeof(buf),
> +		 "/sys/kernel/debug/tracing/events/%s/id", probe_name);
> +	efd = open(buf, O_RDONLY, 0);
> +	if (CHECK(efd < 0, "open", "err %d errno %d\n", efd, errno))
> +		goto close_prog;
> +	bytes = read(efd, buf, sizeof(buf));
> +	close(efd);
> +	if (CHECK(bytes <= 0 || bytes >= sizeof(buf), "read",
> +		  "bytes %d errno %d\n", bytes, errno))
> +		goto close_prog;
> +
> +	attr.config = strtol(buf, NULL, 0);
> +	attr.type = PERF_TYPE_TRACEPOINT;
> +	attr.sample_type = PERF_SAMPLE_RAW;
> +	attr.sample_period = 1;
> +	attr.wakeup_events = 1;
> +
> +	pmu_fd = syscall(__NR_perf_event_open, &attr, getpid(), -1, -1, 0);
> +	if (CHECK(pmu_fd < 0, "perf_event_open", "err %d errno %d\n", pmu_fd,
> +		  errno))
> +		goto close_prog;
> +
> +	err = ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE, 0);
> +	if (CHECK(err, "perf_event_ioc_enable", "err %d errno %d\n", err,
> +		  errno))
> +		goto close_pmu;
> +
> +	err = ioctl(pmu_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
> +	if (CHECK(err, "perf_event_ioc_set_bpf", "err %d errno %d\n", err,
> +		  errno))
> +		goto close_pmu;

The whole thing above related to tracepoint can be simplified. Please 
see prog_tests/stacktrace_map.c.

> +
> +	/* trigger some syscalls */
> +	sleep(1);
> +
> +	err = bpf_map_lookup_elem(ns_pid_map_fd, &key, &nspid);
> +	if (CHECK(err, "bpf_map_lookup_elem", "err %d errno %d\n", err, errno))
> +		goto close_pmu;
> +
> +	if (CHECK(nspid != pid, "compare nspid vs pid",
> +		  "kern nspid %u user pid %u", nspid, pid))
> +		goto close_pmu;
> +
> +	exit_code = 0;
> +	printf("%s:PASS\n", argv[0]);
> +
> +close_pmu:
> +	close(pmu_fd);
> +close_prog:
> +	bpf_object__close(obj);
> +cleanup_cgroup_env:
> +	return exit_code;
> +}
> 

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