[PATCH 4/4] module: Add hook for security_kernel_post_read_file()

[Mimi Zohar]

On Tue, 2020-07-07 at 01:19 -0700, Kees Cook wrote:
> Calls to security_kernel_load_data() should be paired with a call to
> security_kernel_post_read_file() with a NULL file argument. Add the
> missing call so the module contents are visible to the LSMs interested
> in measuring the module content. (This also paves the way for moving
> module signature checking out of the module core and into an LSM.)
> 
> Cc: Jessica Yu <jeyu at kernel.org>
> Fixes: c77b8cdf745d ("module: replace the existing LSM hook in init_module")
> Signed-off-by: Kees Cook <keescook at chromium.org>
> ---
>  kernel/module.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 0c6573b98c36..af9679f8e5c6 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2980,7 +2980,12 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
>  		return -EFAULT;
>  	}
>  
> -	return 0;
> +	err = security_kernel_post_read_file(NULL, (char *)info->hdr,
> +					     info->len, READING_MODULE);

There was a lot of push back on calling security_kernel_read_file()
with a NULL file descriptor here.[1]  The result was defining a new
security hook - security_kernel_load_data - and enumeration -
LOADING_MODULE.  I would prefer calling the same pre and post security
hook.

Mimi

[1] http://kernsec.org/pipermail/linux-security-module-archive/2018-Ma
y/007110.html

> +	if (err)
> +		vfree(info->hdr);
> +
> +	return err;
>  }
>  
>  static void free_copy(struct load_info *info)