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Date:   Mon, 29 Jul 2019 19:56:21 +0200
From:   Christian Brauner <christian@brauner.io>
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kernel@vger.kernel.org, oleg@redhat.com,
        torvalds@linux-foundation.org, arnd@arndb.de,
        ebiederm@xmission.com, joel@joelfernandes.org, tglx@linutronix.de,
        tj@kernel.org, dhowells@redhat.com, jannh@google.com,
        luto@kernel.org, akpm@linux-foundation.org, cyphar@cyphar.com,
        viro@zeniv.linux.org.uk, kernel-team@android.com
Subject: Re: [PATCH v3 1/2] pidfd: add P_PIDFD to waitid()
Message-ID: <20190729175620.uwszsvidnb2cmul4@brauner.io>
References: <20190727222229.6516-1-christian@brauner.io>
 <20190727222229.6516-2-christian@brauner.io>
 <201907290915.8B421306D@keescook>
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On Mon, Jul 29, 2019 at 09:24:38AM -0700, Kees Cook wrote:
> On Sun, Jul 28, 2019 at 12:22:29AM +0200, Christian Brauner wrote:
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index a75b6a7f458a..64bb6893a37d 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -1552,6 +1552,23 @@ static long do_wait(struct wait_opts *wo)
> >  	return retval;
> >  }
> >  
> > +static struct pid *pidfd_get_pid(unsigned int fd)
> > +{
> > +	struct fd f;
> > +	struct pid *pid;
> > +
> > +	f = fdget(fd);
> > +	if (!f.file)
> > +		return ERR_PTR(-EBADF);
> > +
> > +	pid = pidfd_pid(f.file);
> > +	if (!IS_ERR(pid))
> > +		get_pid(pid);
> > +
> > +	fdput(f);
> > +	return pid;
> > +}
> > +
> >  static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
> >  			  int options, struct rusage *ru)
> >  {
> > @@ -1574,19 +1591,29 @@ static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
> >  		type = PIDTYPE_PID;
> >  		if (upid <= 0)
> >  			return -EINVAL;
> > +
> > +		pid = find_get_pid(upid);
> >  		break;
> >  	case P_PGID:
> >  		type = PIDTYPE_PGID;
> >  		if (upid <= 0)
> >  			return -EINVAL;
> > +
> > +		pid = find_get_pid(upid);
> > +		break;
> > +	case P_PIDFD:
> > +		type = PIDTYPE_PID;
> > +		if (upid < 0)
> > +			return -EINVAL;
> > +
> > +		pid = pidfd_get_pid(upid);
> > +		if (IS_ERR(pid))
> > +			return PTR_ERR(pid);
> 
> I spent some time convincing myself that this early bail out was
> correct. It seems this path is only reachable in the EBADF case, so that
> makes sense. The other failure modes in this switch all give a NULL pid
> so that the final do_wait() returns ECHILD. So, as long as that's
> intentional (which I think it is), this all looks fine. :)

Yep, it is. I didn't want to refactor that out of do_wait(). :)

Thanks!
Christian

> 
> Reviewed-by: Kees Cook <keescook@chromium.org>