Re: [PATCH 3/3] RFC: p9auth: add p9auth fs

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Oleg Nesterov (oleg@redhat.com):
> On 04/27, Serge E. Hallyn wrote:
> >
> > This introduces a Plan 9 style setuid capability filesystem.
> > See Documentation/p9auth.txt for a description of how to use this.
> 
> Can't comment these changes due to the lack of knowledge, just
> a couple of minor nits.

Thanks, Oleg.

> > +static ssize_t p9auth_use_write(struct file *file, const char __user *buffer,
> > +			       size_t count, loff_t *ppos)
> > +{
> > +	ssize_t retval = -ENOMEM;
> > +	char *user_buf;
> > +
> > +	if (mutex_lock_interruptible(&cap_mutex))
> > +		return -EINTR;
> 
> EINTR doesn't look exactly right here, especially if TIF_SIGPENDING is
> spurious. Probably ERESTARTNOINTR makes more sense. Or mutex_lock_killable().

Ashwin had had this as ERESTARTSYS I believe.  I'd read something about
userspace should only see -EINTR so I changed it.  Sounds like I need
to follow the caller chain some more and learn a thing or two, before
I repost.

> > +	user_buf = kzalloc(count+1, GFP_KERNEL);
> 
> Probably this is OK, but it looks a bit strange we do no check that
> count is not too large.

Yes, I should check that, thanks!

> > +	if (copy_from_user(user_buf, buffer, count)) {
> > +		retval = -EFAULT;
> > +		goto out;
> > +	}
> > +
> > +	retval = use_setuid_capability(user_buf);
> 
> It seems that use_setuid_capability() pathes assume that user_buf is
> null terminated? Say, parse_user_capability() does kstrdup(user_buf).

I kzalloc()d to count+1 before, and only copy_from_user() count bytes,
so the last byte should always be 0.

Thanks again,

-serge