bpf: Add bpf_get_task_cmdline kfunc

kernel/bpf/helpers.c

@@ -2688,6 +2688,27 @@ __bpf_kfunc struct task_struct *bpf_task_from_pid(s32 pid)
 	return p;
 }
 
+/*
+ * bpf_get_task_cmdline - Get the cmdline to a buffer
+ *
+ * @task: The task whose cmdline to get.
+ * @buffer: The buffer to save cmdline info.
+ * @len: The length of the buffer.
+ *
+ * Return: the size of the cmdline field copied. Note that the copy does
+ * not guarantee an ending NULL byte. A negative error code on failure.
+ */
+__bpf_kfunc int bpf_get_task_cmdline(struct task_struct *task, char *buffer, size_t len)
+{
+	int ret;
+
+	ret = get_cmdline(task, buffer, len);
+	if (ret < 0)
+		memset(buffer, 0, len);
+
+	return ret;
+}
+
 /**
  * bpf_task_from_vpid - Find a struct task_struct from its vpid by looking it up
  * in the pid namespace of the current task. If a task is returned, it must
@@ -4428,6 +4449,7 @@ BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_from_vpid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_throw)
+BTF_ID_FLAGS(func, bpf_get_task_cmdline, KF_SLEEPABLE | KF_TRUSTED_ARGS)
 #ifdef CONFIG_BPF_EVENTS
 BTF_ID_FLAGS(func, bpf_send_signal_task, KF_TRUSTED_ARGS)
 #endif

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

@@ -156,6 +156,10 @@ static const char * const vpid_success_tests[] = {
 	"test_task_from_vpid_invalid",
 };
 
+static const char * const cmdline_success_tests[] = {
+	"test_get_task_cmdline",
+};
+
 void test_task_kfunc(void)
 {
 	int i;
@@ -174,5 +178,12 @@ void test_task_kfunc(void)
 		run_vpid_success_test(vpid_success_tests[i]);
 	}
 
+	for (i = 0; i < ARRAY_SIZE(cmdline_success_tests); i++) {
+		if (!test__start_subtest(cmdline_success_tests[i]))
+			continue;
+
+		run_success_test(cmdline_success_tests[i]);
+	}
+
 	RUN_TESTS(task_kfunc_failure);
 }

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

@@ -367,6 +367,19 @@ int BPF_PROG(task_kfunc_acquire_trusted_walked, struct task_struct *task, u64 cl
 	return 0;
 }
 
+SEC("lsm.s/task_alloc")
+int BPF_PROG(test_get_task_cmdline, struct task_struct *task)
+{
+	char buf[64];
+	int ret;
+
+	ret = bpf_get_task_cmdline(task, buf, sizeof(buf));
+	if (ret < 0)
+		err = 1;
+
+	return 0;
+}
+
 SEC("syscall")
 int test_task_from_vpid_current(const void *ctx)
 {