selftests/bpf: Add tests for bpf_fget_task() kfunc

This patch adds test cases for bpf_fget_task() kfunc.

test_bpf_fget_task is used to test obtaining struct file based on
the file descriptor in the current process.

bpf_fget_task_null_task and bpf_fget_task_untrusted_task are used to
test the failure cases of passing NULL or untrusted pointer as argument.

Signed-off-by: Juntong Deng <[email protected]>

tools/testing/selftests/bpf/bpf_experimental.h

@@ -221,6 +221,14 @@ extern void bpf_put_file(struct file *file) __ksym;
  */
 extern int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz) __ksym;
 
+/* Description
+ *	Get a pointer to the struct file corresponding to the task file descriptor
+ *	Note that this function acquires a reference to struct file.
+ * Returns
+ *	The corresponding struct file pointer if found, otherwise returns NULL
+ */
+extern struct file *bpf_fget_task(struct task_struct *task, unsigned int fd) __ksym;
+
 /* This macro must be used to mark the exception callback corresponding to the
  * main program. For example:
  *

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

@@ -9,6 +9,8 @@
 #include <test_progs.h>
 #include "test_get_xattr.skel.h"
 #include "test_fsverity.skel.h"
+#include "test_fget_task.skel.h"
+#include "fs_kfuncs_failure.skel.h"
 
 static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
 
@@ -139,11 +141,55 @@ static void test_fsverity(void)
 	remove(testfile);
 }
 
+static void test_fget_task(void)
+{
+	int pipefd[2], prog_fd, err = 0;
+	struct test_fget_task *skel;
+	struct bpf_program *prog;
+
+	skel = test_fget_task__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	if (!ASSERT_OK(skel->bss->err, "pre_test_err"))
+		goto cleanup_skel;
+
+	prog = bpf_object__find_program_by_name(skel->obj, "test_bpf_fget_task");
+	if (!ASSERT_OK_PTR(prog, "find_program_by_name"))
+		goto cleanup_skel;
+
+	prog_fd = bpf_program__fd(prog);
+	if (!ASSERT_GT(prog_fd, -1, "bpf_program__fd"))
+		goto cleanup_skel;
+
+	if (pipe(pipefd) < 0)
+		goto cleanup_skel;
+
+	skel->bss->test_fd1 = pipefd[0];
+	skel->bss->test_fd2 = pipefd[1];
+
+	err = bpf_prog_test_run_opts(prog_fd, NULL);
+	if (!ASSERT_OK(err, "prog_test_run"))
+		goto cleanup_pipe;
+
+	ASSERT_OK(skel->bss->err, "run_bpf_fget_task_test_failure");
+cleanup_pipe:
+	close(pipefd[0]);
+	close(pipefd[1]);
+cleanup_skel:
+	test_fget_task__destroy(skel);
+}
+
 void test_fs_kfuncs(void)
 {
 	if (test__start_subtest("xattr"))
 		test_xattr();
 
 	if (test__start_subtest("fsverity"))
 		test_fsverity();
+
+	if (test__start_subtest("fget_task"))
+		test_fget_task();
+
+	RUN_TESTS(fs_kfuncs_failure);
 }

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

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("syscall")
+__failure __msg("Possibly NULL pointer passed to trusted arg0")
+int bpf_fget_task_null_task(void *ctx)
+{
+	struct task_struct *task = NULL;
+
+	bpf_fget_task(task, 1);
+
+	return 0;
+}
+
+SEC("syscall")
+__failure __msg("R1 must be referenced or trusted")
+int bpf_fget_task_untrusted_task(void *ctx)
+{
+	struct task_struct *task;
+
+	task = bpf_get_current_task_btf()->parent;
+
+	bpf_fget_task(task, 1);
+
+	return 0;
+}

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

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+#include "task_kfunc_common.h"
+
+char _license[] SEC("license") = "GPL";
+
+int err, test_fd1, test_fd2;
+
+SEC("syscall")
+int test_bpf_fget_task(void *ctx)
+{
+	struct task_struct *task;
+	struct file *file;
+
+	task = bpf_get_current_task_btf();
+	if (task == NULL) {
+		err = 1;
+		return 0;
+	}
+
+	file = bpf_fget_task(task, test_fd1);
+	if (file == NULL) {
+		err = 2;
+		return 0;
+	}
+
+	bpf_put_file(file);
+
+	file = bpf_fget_task(task, test_fd2);
+	if (file == NULL) {
+		err = 3;
+		return 0;
+	}
+
+	bpf_put_file(file);
+
+	file = bpf_fget_task(task, 9999);
+	if (file != NULL) {
+		err = 4;
+		bpf_put_file(file);
+	}
+
+	return 0;
+}