Kernel: Update process promise states on execve() and fork()

We now move the execpromises state into the regular promises, and clear
the execpromises state.

Also make sure to duplicate the promise state on fork.

This fixes an issue where "su" would launch a shell which immediately
crashed due to not having pledged "stdio".

Kernel/Process.h

@@ -637,6 +637,7 @@ private:
 
     bool m_has_promises { false };
     u32 m_promises { 0 };
+    bool m_has_execpromises { false };
     u32 m_execpromises { 0 };
 
     VeilState m_veil_state { VeilState::None };

Kernel/Syscalls/execve.cpp

@@ -544,6 +544,10 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
     m_environment = environment;
 
     m_promises = m_execpromises;
+    m_has_promises = m_has_execpromises;
+
+    m_execpromises = 0;
+    m_has_execpromises = false;
 
     m_veil_state = VeilState::None;
     m_unveiled_paths.clear();

Kernel/Syscalls/fork.cpp

@@ -43,6 +43,8 @@ pid_t Process::sys$fork(RegisterState& regs)
     child->m_root_directory_relative_to_global_root = m_root_directory_relative_to_global_root;
     child->m_promises = m_promises;
     child->m_execpromises = m_execpromises;
+    child->m_has_promises = m_has_promises;
+    child->m_has_execpromises = m_has_execpromises;
     child->m_veil_state = m_veil_state;
     child->m_unveiled_paths = m_unveiled_paths.deep_copy();
     child->m_fds = m_fds;

Kernel/Syscalls/pledge.cpp

@@ -84,7 +84,9 @@ int Process::sys$pledge(Userspace<const Syscall::SC_pledge_params*> user_params)
             return -EPERM;
     }
 
-    m_has_promises = true;
+    m_has_promises = m_has_promises || !promises.is_null();
+    m_has_execpromises = m_has_execpromises || !execpromises.is_null();
+
     m_promises = new_promises;
     m_execpromises = new_execpromises;