Kernel: Remove waitpid() debug messages and add more checks

kernel/include/std/errno.h

@@ -7,6 +7,7 @@
 #define E2BIG 7
 #define ENOEXEC 8
 #define EBADF 9
+#define ECHILD 10
 #define EAGAIN 11
 #define ENOMEM 12
 #define EACCES 13

kernel/src/thread/Scheduler.cpp

@@ -510,10 +510,16 @@ void sys_waitpid(Context* context, long pid, int* wstatus,
         child = Scheduler::find_by_pid(pid);
         if (!child)
         {
-            context->rax = -ESRCH;
+            context->rax = -ECHILD;
             return;
         }
     }
+    if (child->ppid != sched_current_task->id)
+    {
+        // We are trying to call waitpid() on a task that isn't a child of ours. This is not allowed.
+        context->rax = -ECHILD;
+        return;
+    }
     if (child->state != child->Dying)
     {
         if (options & WNOHANG)
@@ -531,7 +537,6 @@ void sys_waitpid(Context* context, long pid, int* wstatus,
                 return;
             }
         }
-        kdbgln("blocking wait on pid %ld", pid);
         sched_current_task->state = sched_current_task->Blocking;
         sched_current_task->block_reason = BlockReason::Waiting;
         sched_current_task->blocking_wait_info.wait_pid = pid;
@@ -583,6 +588,8 @@ bool Task::is_wait_still_blocking()
     else
     {
         child = Scheduler::find_by_pid(blocking_wait_info.wait_pid);
+        ASSERT(child); // since sys_waitpid should have validated this child, and the only way for it to disappear from
+                       // the process list is for someone to wait for it, this should be pretty safe.
         if (child->state != child->Dying) return true;
         else
             return false;
@@ -596,8 +603,6 @@ void Task::resume_wait()
     Task* child = Scheduler::find_by_pid(blocking_wait_info.wait_pid);
     ASSERT(child); // This should also already have been validated.
 
-    kdbgln("resuming wait on child %ld", child->id);
-
     if (blocking_wait_info.wstatus)
     {
         *blocking_wait_info.wstatus = (int)(child->exit_status & 0xff);

libs/libc/include/errno.h

@@ -12,6 +12,7 @@ extern int errno;
 #define E2BIG 7       // Argument list too long
 #define ENOEXEC 8     // Exec format error
 #define EBADF 9       // Bad file descriptor
+#define ECHILD 10     // No child processes
 #define EAGAIN 11     // Resource temporarily unavailable
 #define ENOMEM 12     // Cannot allocate memory
 #define EACCES 13     // Permission denied

libs/libc/src/string.cpp

@@ -265,6 +265,7 @@ extern "C"
         case E2BIG: return "Argument list too long";
         case ENOEXEC: return "Exec format error";
         case EBADF: return "Bad file descriptor";
+        case ECHILD: return "No child processes";
         case EAGAIN: return "Resource temporarily unavailable";
         case ENOMEM: return "Cannot allocate memory";
         case EACCES: return "Permission denied";