Re: [PATCH] /proc/*/environ: wrong placing of ptrace_may_attach() check

[Alexey Dobriyan <adobriyan@sw.ru>]

On Tue, May 29, 2007 at 05:16:23PM -0700, Andrew Morton wrote:
> On Mon, 28 May 2007 17:41:57 +0400
> Alexey Dobriyan <adobriyan@sw.ru> wrote:

> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -204,12 +204,17 @@ static int proc_pid_environ(struct task_
> >  	int res = 0;
> >  	struct mm_struct *mm = get_task_mm(task);
> >  	if (mm) {
> > -		unsigned int len = mm->env_end - mm->env_start;
> > +		unsigned int len;
> > +
> > +		res = -ESRCH;
> > +		if (!ptrace_may_attach(task))
> > +			goto out;
> > +
> > +		len  = mm->env_end - mm->env_start;
> >  		if (len > PAGE_SIZE)
> >  			len = PAGE_SIZE;
> >  		res = access_process_vm(task, mm->env_start, buffer, len, 0);
> > -		if (!ptrace_may_attach(task))
> > -			res = -ESRCH;
> > +out:
> >  		mmput(mm);
> >  	}
> >  	return res;
>
> What's wrong with the existing code?  It's a bit dopey-looking and can, I
> guess, permit a task to cause a pagefault in an mm which it doesn't have
> permission to read from.  But is there some more serious problem being
> fixed here?

I think not, because environment will be copied from target task, stay
in kernel tmp buffer, but not copied to target buffer due to -ESRCH.
But such code is asking for problems.