[PATCH 2/7] exec: Factor out alloc_bprm

[Kees Cook]

On Tue, Jul 14, 2020 at 08:29:05AM -0500, Eric W. Biederman wrote:
> 
> Currently it is necessary for the usermode helper code and the code
> that launches init to use set_fs so that pages coming from the kernel
> look like they are coming from userspace.
> 
> To allow that usage of set_fs to be removed cleanly the argument
> copying from userspace needs to happen earlier.  Move the allocation
> of the bprm into it's own function (alloc_bprm) and move the call of
> alloc_bprm before unshare_files so that bprm can ultimately be
> allocated, the arguments can be placed on the new stack, and then the
> bprm can be passed into the core of exec.
> 
> Neither the allocation of struct binprm nor the unsharing depend upon each
> other so swapping the order in which they are called is trivially safe.
> 
> To keep things consistent the order of cleanup at the end of
> do_execve_common swapped to match the order of initialization.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>

Reviewed-by: Kees Cook <keescook at chromium.org>

-- 
Kees Cook