Commit bfb4a2b9 authored by Rolf Eike Beer's avatar Rolf Eike Beer Committed by Kees Cook
Browse files

exec: simplify initial stack size expansion 



I had a hard time trying to understand completely why it is using vm_end in
one side of the expression and vm_start in the other one, and using
something in the "if" clause that is not an exact copy of what is used
below. The whole point is that the stack_size variable that was used in the
"if" clause is the difference between vm_start and vm_end, which is not far
away but makes this thing harder to read than it must be.

Signed-off-by: default avatarRolf Eike Beer <eb@emlix.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/2017429.gqNitNVd0C@mobilepool36.emlix.com
parent 8f6e3f9e

fs/exec.c

+5 −8
Original line number Diff line number Diff line
@@ -843,16 +843,13 @@ int setup_arg_pages(struct linux_binprm *bprm, 
	 * will align it up.

	 */

	rlim_stack = bprm->rlim_stack.rlim_cur & PAGE_MASK;



	stack_expand = min(rlim_stack, stack_size + stack_expand);



#ifdef CONFIG_STACK_GROWSUP

	if (stack_size + stack_expand > rlim_stack)

		stack_base = vma->vm_start + rlim_stack;

	else

		stack_base = vma->vm_end + stack_expand;

	stack_base = vma->vm_start + stack_expand;

#else

	if (stack_size + stack_expand > rlim_stack)

		stack_base = vma->vm_end - rlim_stack;

	else

		stack_base = vma->vm_start - stack_expand;

	stack_base = vma->vm_end - stack_expand;

#endif

	current->mm->start_stack = bprm->p;

	ret = expand_stack(vma, stack_base);