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exec: simplify initial stack size expansion

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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: Rolf Eike Beer <eb@emlix.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/2017429.gqNitNVd0C@mobilepool36.emlix.com
This commit is contained in:
Rolf Eike Beer 2022-10-19 09:32:35 +02:00 • committed by Kees Cook
parent 8f6e3f9e5a
commit bfb4a2b958
1 changed files with 5 additions and 8 deletions
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13
fs/exec.c
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@ -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);