[PATCH gnumach] Check for null ports in task_set_essential, task_set_name and thread_set_name.

[Flavio Cruz]

Otherwise, it is easy to crash the kernel if userland passes arbitrary port
names.
---
 kern/task.c   | 6 ++++++
 kern/thread.c | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/kern/task.c b/kern/task.c
index 60ab4d7..dfba04d 100644
--- a/kern/task.c
+++ b/kern/task.c
@@ -1165,6 +1165,9 @@ task_set_name(
        task_t                  task,
        const_kernel_debug_name_t       name)
 {
+       if (task == TASK_NULL)
+               return KERN_INVALID_ARGUMENT;
+
        strncpy(task->name, name, sizeof task->name - 1);
        task->name[sizeof task->name - 1] = '\0';
        return KERN_SUCCESS;
@@ -1181,6 +1184,9 @@ task_set_essential(
        task_t                  task,
        boolean_t               essential)
 {
+       if (task == TASK_NULL)
+               return KERN_INVALID_ARGUMENT;
+
        task->essential = !!essential;
        return KERN_SUCCESS;
 }
diff --git a/kern/thread.c b/kern/thread.c
index 2eab1ca..eb73590 100644
--- a/kern/thread.c
+++ b/kern/thread.c
@@ -2640,6 +2640,9 @@ thread_set_name(
        thread_t        thread,
        const_kernel_debug_name_t       name)
 {
+       if (thread == THREAD_NULL)
+               return KERN_INVALID_ARGUMENT;
+
        strncpy(thread->name, name, sizeof thread->name - 1);
        thread->name[sizeof thread->name - 1] = '\0';
        return KERN_SUCCESS;
-- 
2.39.2