Re: [v10][PATCH 8/9] Define clone_with_pids() syscall

[Sukadev Bhattiprolu <sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>]

Dave Hansen [dave-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org] wrote:
| On Sun, 2009-11-01 at 12:45 -0800, Sukadev Bhattiprolu wrote:
| > +int sys_clone_with_pids(struct pt_regs *regs)
| > +{
| ...
| > +       rc = copy_from_user(&kcs, ucs, sizeof(kcs));
| > +       if (rc)
| > +               return -EFAULT;
| > +
| > +       /*
| > +        * TODO: If size of clone_args is not what the kernel expects, it
| > +        *       could be that kernel is newer and has an extended structure.
| > +        *       When that happens, this check needs to be smarter (and we
| > +        *       need an additional copy_from_user()). For now, assume exact
| > +        *       match.
| > +        */
| > +       if (kcs.clone_args_size != sizeof(kcs))
| > +               return -EINVAL;
| > +
| > +       /*
| > +        * To avoid future compatibility issues, ensure unused fields are 0.
| > +        */
| > +       if (kcs.reserved1 || kcs.clone_flags_high)
| > +               return -EINVAL;
| 
| Suka, is there a reason we don't have these bits in some
| arch-independent code?  I would have thought the stuff in the
| process_32.c code would be just as thin a wrapper as possible to unwrap
| the pt_regs and call into generic code.

Yes, it can be in arch independent code: but couple of minor inconvinences:

	- currently the arch independent code does not know about the
	  'clone_args' structure. This helps keep this patchset smaller.
	  It could know about it in the future (when more flags are added).

	- and we need to check these *before* unwrapping the values from
	  pt_regs.

Well, you are right. Will define 'check_clone_with_pids_params()' in
kernel/fork.c and call it here before unwrapping the params.

Suka