selftests/bpf: Fix stat probe in d_path test

Some kernels builds might inline vfs_getattr call within fstat
syscall code path, so fentry/vfs_getattr trampoline is not called.

Add security_inode_getattr to allowlist and switch the d_path test stat
trampoline to security_inode_getattr.

Keeping dentry_open and filp_close, because they are in their own
files, so unlikely to be inlined, but in case they are, adding
security_file_open.

Adding flags that indicate trampolines were called and failing
the test if any of them got missed, so it's easier to identify
the issue next time.

Fixes: e4d1af4b ("selftests/bpf: Add test for d_path helper")
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200918112338.2618444-1-jolsa@kernel.org

kernel/trace/bpf_trace.c

@@ -1114,6 +1114,14 @@ BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf, u32, sz)
 }
 
 BTF_SET_START(btf_allowlist_d_path)
+#ifdef CONFIG_SECURITY
+BTF_ID(func, security_file_permission)
+BTF_ID(func, security_inode_getattr)
+BTF_ID(func, security_file_open)
+#endif
+#ifdef CONFIG_SECURITY_PATH
+BTF_ID(func, security_path_truncate)
+#endif
 BTF_ID(func, vfs_truncate)
 BTF_ID(func, vfs_fallocate)
 BTF_ID(func, dentry_open)

tools/testing/selftests/bpf/prog_tests/d_path.c

@@ -120,6 +120,16 @@ void test_d_path(void)
 	if (err < 0)
 		goto cleanup;
 
+	if (CHECK(!bss->called_stat,
+		  "stat",
+		  "trampoline for security_inode_getattr was not called\n"))
+		goto cleanup;
+
+	if (CHECK(!bss->called_close,
+		  "close",
+		  "trampoline for filp_close was not called\n"))
+		goto cleanup;
+
 	for (int i = 0; i < MAX_FILES; i++) {
 		CHECK(strncmp(src.paths[i], bss->paths_stat[i], MAX_PATH_LEN),
 		      "check",

tools/testing/selftests/bpf/progs/test_d_path.c

@@ -15,7 +15,10 @@ char paths_close[MAX_FILES][MAX_PATH_LEN] = {};
 int rets_stat[MAX_FILES] = {};
 int rets_close[MAX_FILES] = {};
 
-SEC("fentry/vfs_getattr")
+int called_stat = 0;
+int called_close = 0;
+
+SEC("fentry/security_inode_getattr")
 int BPF_PROG(prog_stat, struct path *path, struct kstat *stat,
 	     __u32 request_mask, unsigned int query_flags)
 {
@@ -23,6 +26,8 @@ int BPF_PROG(prog_stat, struct path *path, struct kstat *stat,
 	__u32 cnt = cnt_stat;
 	int ret;
 
+	called_stat = 1;
+
 	if (pid != my_pid)
 		return 0;
 
@@ -42,6 +47,8 @@ int BPF_PROG(prog_close, struct file *file, void *id)
 	__u32 cnt = cnt_close;
 	int ret;
 
+	called_close = 1;
+
 	if (pid != my_pid)
 		return 0;