Re: [RFC c/r 4/4] c/r: prctl: Extend PR_SET_MM to set up moremm_struct entries

[Kees Cook]

On Fri, Jan 27, 2012 at 9:53 AM, Cyrill Gorcunov <gorcunov@xxxxxxxxxx> wrote:
> +               if (opt == PR_SET_MM_START_STACK)
> +                       mm->start_stack = addr;
> +               else if (opt == PR_SET_MM_ARG_START)
> +                       mm->arg_start = addr;
> +               else if (opt == PR_SET_MM_ARG_END)
> +                       mm->arg_end = addr;
> +               else if (opt == PR_SET_MM_ENV_START)
> +                       mm->env_start = addr;
> +               else if (opt == PR_SET_MM_ENV_END)
> +                       mm->env_end = addr;
> +               break;

Why not a switch statement here? Not that it really matters. :)

> +
> +       case PR_SET_MM_AUXV:
> +               if (arg4 > sizeof(mm->saved_auxv))
> +                       goto out;
> +               up_read(&mm->mmap_sem);
> +
> +               error = -EFAULT;
> +               if (!copy_from_user(mm->saved_auxv, (const void __user *)addr, arg4))
> +                       error = 0;
> +
> +               return error;

Is the mmap_sem released here because of the copy_from_user()? Is it
still safe to write to saved_auxv?

-Kees

-- 
Kees Cook
ChromeOS Security
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