[PATCH bpf-next v13 2/2] selftests/bpf: test for bpf_get_fd_path() from tracepoint

[Wenbo Zhang <ethercflow@gmail.com>]

trace fstat events by tracepoint syscalls/sys_enter_newfstat, and handle
events only produced by test_file_fd_path, which call fstat on several
different types of files to test bpf_fd_file_path's feature.

v5->v6: addressed Gregg and Yonghong's feedback
- rename to get_fd_path
- change sys_enter_newfstat_args's fd type to long to fix issue on
big-endian machines

v4->v5: addressed Andrii's feedback
- pass NULL for opts as bpf_object__open_file's PARAM2, as not really
using any
- modify patch subject to keep up with test code
- as this test is single-threaded, so use getpid instead of SYS_gettid
- remove unnecessary parens around check which after if (i < 3)
- in kern use bpf_get_current_pid_tgid() >> 32 to fit getpid() in
userspace part
- with the patch adding helper as one patch series

v3->v4: addressed Andrii's feedback
- use a set of fd instead of fds array
- use global variables instead of maps (in v3, I mistakenly thought that
the bpf maps are global variables.)
- remove uncessary global variable path_info_index
- remove fd compare as the fstat's order is fixed

v2->v3: addressed Andrii's feedback
- use global data instead of perf_buffer to simplified code

v1->v2: addressed Daniel's feedback
- rename bpf_fd2path to bpf_get_file_path to be consistent with other
helper's names

Signed-off-by: Wenbo Zhang <ethercflow@gmail.com>
---
 .../selftests/bpf/prog_tests/get_fd_path.c    | 171 ++++++++++++++++++
 .../selftests/bpf/progs/test_get_fd_path.c    |  43 +++++
 2 files changed, 214 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/get_fd_path.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_get_fd_path.c

diff --git a/tools/testing/selftests/bpf/prog_tests/get_fd_path.c b/tools/testing/selftests/bpf/prog_tests/get_fd_path.c
new file mode 100644
index 000000000000..5cf58028a8d2
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/get_fd_path.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <test_progs.h>
+#include <sys/stat.h>
+#include <linux/sched.h>
+#include <sys/syscall.h>
+
+#define MAX_PATH_LEN		128
+#define MAX_FDS			7
+#define MAX_EVENT_NUM		16
+
+static struct fd_path_test_data {
+	pid_t pid;
+	__u32 cnt;
+	__u32 fds[MAX_EVENT_NUM];
+	char paths[MAX_EVENT_NUM][MAX_PATH_LEN];
+} src, dst;
+
+static int set_pathname(int fd)
+{
+	char buf[MAX_PATH_LEN];
+
+	snprintf(buf, MAX_PATH_LEN, "/proc/%d/fd/%d", src.pid, fd);
+	src.fds[src.cnt] = fd;
+	return readlink(buf, src.paths[src.cnt++], MAX_PATH_LEN);
+}
+
+static int trigger_fstat_events(pid_t pid)
+{
+	int pipefd[2] = { -1, -1 };
+	int sockfd = -1, procfd = -1, devfd = -1;
+	int localfd = -1, indicatorfd = -1;
+	struct stat fileStat;
+	int ret = -1;
+
+	/* unmountable pseudo-filesystems */
+	if (CHECK_FAIL(pipe(pipefd) < 0))
+		return ret;
+	/* unmountable pseudo-filesystems */
+	sockfd = socket(AF_INET, SOCK_STREAM, 0);
+	if (CHECK_FAIL(sockfd < 0))
+		goto out_close;
+	/* mountable pseudo-filesystems */
+	procfd = open("/proc/self/comm", O_RDONLY);
+	if (CHECK_FAIL(procfd < 0))
+		goto out_close;
+	devfd = open("/dev/urandom", O_RDONLY);
+	if (CHECK_FAIL(devfd < 0))
+		goto out_close;
+	localfd = open("/tmp/fd2path_loadgen.txt", O_CREAT | O_RDONLY);
+	if (CHECK_FAIL(localfd < 0))
+		goto out_close;
+	/* bpf_get_fd_path will return path with (deleted) */
+	remove("/tmp/fd2path_loadgen.txt");
+	indicatorfd = open("/tmp/", O_PATH);
+	if (CHECK_FAIL(indicatorfd < 0))
+		goto out_close;
+
+	src.pid = pid;
+
+	ret = set_pathname(pipefd[0]);
+	if (CHECK_FAIL(ret < 0))
+		goto out_close;
+	ret = set_pathname(pipefd[1]);
+	if (CHECK_FAIL(ret < 0))
+		goto out_close;
+	ret = set_pathname(sockfd);
+	if (CHECK_FAIL(ret < 0))
+		goto out_close;
+	ret = set_pathname(procfd);
+	if (CHECK_FAIL(ret < 0))
+		goto out_close;
+	ret = set_pathname(devfd);
+	if (CHECK_FAIL(ret < 0))
+		goto out_close;
+	ret = set_pathname(localfd);
+	if (CHECK_FAIL(ret < 0))
+		goto out_close;
+	ret = set_pathname(indicatorfd);
+	if (CHECK_FAIL(ret < 0))
+		goto out_close;
+
+	fstat(pipefd[0], &fileStat);
+	fstat(pipefd[1], &fileStat);
+	fstat(sockfd, &fileStat);
+	fstat(procfd, &fileStat);
+	fstat(devfd, &fileStat);
+	fstat(localfd, &fileStat);
+	fstat(indicatorfd, &fileStat);
+
+out_close:
+	close(indicatorfd);
+	close(localfd);
+	close(devfd);
+	close(procfd);
+	close(sockfd);
+	close(pipefd[1]);
+	close(pipefd[0]);
+
+	return ret;
+}
+
+void test_get_fd_path(void)
+{
+	const char *prog_name = "tracepoint/syscalls/sys_enter_newfstat";
+	const char *obj_file = "test_get_fd_path.o";
+	int err, results_map_fd, duration = 0;
+	struct bpf_program *tp_prog = NULL;
+	struct bpf_link *tp_link = NULL;
+	struct bpf_object *obj = NULL;
+	const int zero = 0;
+
+	obj = bpf_object__open_file(obj_file, NULL);
+	if (CHECK(IS_ERR(obj), "obj_open_file", "err %ld\n", PTR_ERR(obj)))
+		return;
+
+	tp_prog = bpf_object__find_program_by_title(obj, prog_name);
+	if (CHECK(!tp_prog, "find_tp",
+		  "prog '%s' not found\n", prog_name))
+		goto cleanup;
+
+	err = bpf_object__load(obj);
+	if (CHECK(err, "obj_load", "err %d\n", err))
+		goto cleanup;
+
+	results_map_fd = bpf_find_map(__func__, obj, "test_get.bss");
+	if (CHECK(results_map_fd < 0, "find_bss_map",
+		  "err %d\n", results_map_fd))
+		goto cleanup;
+
+	tp_link = bpf_program__attach_tracepoint(tp_prog, "syscalls",
+						 "sys_enter_newfstat");
+	if (CHECK(IS_ERR(tp_link), "attach_tp",
+		  "err %ld\n", PTR_ERR(tp_link))) {
+		tp_link = NULL;
+		goto cleanup;
+	}
+
+	dst.pid = getpid();
+	err = bpf_map_update_elem(results_map_fd, &zero, &dst, 0);
+	if (CHECK(err, "update_elem",
+		  "failed to set pid filter: %d\n", err))
+		goto cleanup;
+
+	err = trigger_fstat_events(dst.pid);
+	if (CHECK_FAIL(err < 0))
+		goto cleanup;
+
+	err = bpf_map_lookup_elem(results_map_fd, &zero, &dst);
+	if (CHECK(err, "get_results",
+		  "failed to get results: %d\n", err))
+		goto cleanup;
+
+	for (int i = 0; i < MAX_FDS; i++) {
+		if (i < 3)
+			CHECK((dst.paths[i][0] != '0'), "get_fd_path",
+			      "failed to filter fs [%d]: %u(%s) vs %u(%s)\n",
+			      i, src.fds[i], src.paths[i], dst.fds[i],
+			      dst.paths[i]);
+		else
+			CHECK(strncmp(src.paths[i], dst.paths[i], MAX_PATH_LEN),
+			      "get_fd_path",
+			      "failed to get path[%d]: %u(%s) vs %u(%s)\n",
+			      i, src.fds[i], src.paths[i], dst.fds[i],
+			      dst.paths[i]);
+	}
+
+cleanup:
+	bpf_link__destroy(tp_link);
+	bpf_object__close(obj);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_get_fd_path.c b/tools/testing/selftests/bpf/progs/test_get_fd_path.c
new file mode 100644
index 000000000000..8bb58f87755e
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_get_fd_path.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <linux/ptrace.h>
+#include <string.h>
+#include <unistd.h>
+#include "bpf_helpers.h"
+#include "bpf_tracing.h"
+
+#define MAX_PATH_LEN		128
+#define MAX_EVENT_NUM		16
+
+static struct fd_path_test_data {
+	pid_t pid;
+	__u32 cnt;
+	__u32 fds[MAX_EVENT_NUM];
+	char paths[MAX_EVENT_NUM][MAX_PATH_LEN];
+} data;
+
+struct sys_enter_newfstat_args {
+	unsigned long long pad1;
+	unsigned long long pad2;
+	unsigned long fd;
+};
+
+SEC("tracepoint/syscalls/sys_enter_newfstat")
+int bpf_prog(struct sys_enter_newfstat_args *args)
+{
+	pid_t pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (pid != data.pid)
+		return 0;
+	if (data.cnt >= MAX_EVENT_NUM)
+		return 0;
+
+	data.fds[data.cnt] = args->fd;
+	bpf_get_fd_path(data.paths[data.cnt], MAX_PATH_LEN, args->fd);
+	data.cnt++;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.17.1