Re: [PATCH] do_fork(): Rename 'stack_size' argument to reflect actual use

[Kees Cook]

On Wed, Mar 4, 2015 at 4:40 AM, Alex Dowad <alexinbeijing@xxxxxxxxx> wrote:
> The 'stack_size' argument is never used to pass a stack size. It's only used when
> forking a kernel thread, in which case it is an argument which should be passed
> to the 'main' function which the kernel thread executes. Hence, rename it to
> 'kthread_arg'.
>
> Signed-off-by: Alex Dowad <alexinbeijing@xxxxxxxxx>

This looks correct to me. Thanks for cleaning it up!

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>
> Hi,
>
> Please have a look at this patch. If this is accepted, I have a series of patches
> ready for a similar cleanup to all the arch-specific implementations of copy_thread()
> (as suggested by Andrew Morton in a private e-mail).
>
> Thank you,
> Alex Dowad
>
>  kernel/fork.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index cf65139..b38a2ae 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1186,10 +1186,12 @@ init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
>   * It copies the registers, and all the appropriate
>   * parts of the process environment (as per the clone
>   * flags). The actual kick-off is left to the caller.
> + *
> + * When copying a kernel thread, 'stack_start' is the function to run.
>   */
>  static struct task_struct *copy_process(unsigned long clone_flags,
>                                         unsigned long stack_start,
> -                                       unsigned long stack_size,
> +                                       unsigned long kthread_arg,
>                                         int __user *child_tidptr,
>                                         struct pid *pid,
>                                         int trace)
> @@ -1401,7 +1403,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>         retval = copy_io(clone_flags, p);
>         if (retval)
>                 goto bad_fork_cleanup_namespaces;
> -       retval = copy_thread(clone_flags, stack_start, stack_size, p);
> +       retval = copy_thread(clone_flags, stack_start, kthread_arg, p);
>         if (retval)
>                 goto bad_fork_cleanup_io;
>
> @@ -1629,8 +1631,8 @@ struct task_struct *fork_idle(int cpu)
>   * it and waits for it to finish using the VM if required.
>   */
>  long do_fork(unsigned long clone_flags,
> -             unsigned long stack_start,
> -             unsigned long stack_size,
> +             unsigned long stack_start, /* or function for kthread to run */
> +             unsigned long kthread_arg,
>               int __user *parent_tidptr,
>               int __user *child_tidptr)
>  {
> @@ -1656,7 +1658,7 @@ long do_fork(unsigned long clone_flags,
>                         trace = 0;
>         }
>
> -       p = copy_process(clone_flags, stack_start, stack_size,
> +       p = copy_process(clone_flags, stack_start, kthread_arg,
>                          child_tidptr, NULL, trace);
>         /*
>          * Do this prior waking up the new thread - the thread pointer
> @@ -1740,7 +1742,7 @@ SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
>                  int, tls_val)
>  #elif defined(CONFIG_CLONE_BACKWARDS3)
>  SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
> -               int, stack_size,
> +               int, ignored,
>                 int __user *, parent_tidptr,
>                 int __user *, child_tidptr,
>                 int, tls_val)
> --
> 2.0.0.GIT
>



-- 
Kees Cook
Chrome OS Security
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