Invoke binary from kernel space

From: hemanth nandish <hemanthluvsfifa@gmail.com>
To: kernelnewbies@kernelnewbies.org
Subject: Invoke binary from kernel space
Date: Fri, 24 Apr 2020 01:23:45 +0530	[thread overview]
Message-ID: <CAEBxVXMoDCyY3nbU0uEWSD2TivgujAYPQhWcLF=BbhrK0y6n=Q@mail.gmail.com> (raw)

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Hello,

I came across the function: call_usermodehelper
This can be used to invoke exec a binary from the kernel space.
It ultimately calls:
call_usermodehelper_exec_async

Which internally does:
retval = do_execve <https://elixir.bootlin.com/linux/v4.7/ident/do_execve>(
getname_kernel <https://elixir.bootlin.com/linux/v4.7/ident/getname_kernel>(
sub_info->path <https://elixir.bootlin.com/linux/v4.7/ident/path>),(const
char __user <https://elixir.bootlin.com/linux/v4.7/ident/__user> *const
__user <https://elixir.bootlin.com/linux/v4.7/ident/__user> *)sub_info->argv
<https://elixir.bootlin.com/linux/v4.7/ident/argv>,(const char __user
<https://elixir.bootlin.com/linux/v4.7/ident/__user> *const __user
<https://elixir.bootlin.com/linux/v4.7/ident/__user> *)sub_info->envp
<https://elixir.bootlin.com/linux/v4.7/ident/envp>);

This function works as expected and a new thread is spawned.
Now when I try to directly call do_execve within my module by passing the
required arguments, I am getting  -EFAULT error.
This is happening in this function:

count(argv, MAX_ARG_STRINGS)

What am I missing here?

Thank you
Hemanth

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