linux-kernel - Re: [PATCH v2 2/5] pid: add pidfd

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Message-ID: <20190329235521.wrtuyoualsvcgz5k@brauner.io>
Date:   Sat, 30 Mar 2019 00:55:22 +0100
From:   Christian Brauner <christian@...uner.io>
To:     Jann Horn <jannh@...gle.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linux API <linux-api@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@...il.com>,
        Jonathan Kowalski <bl0pbl33p@...il.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Daniel Colascione <dancol@...gle.com>
Subject: Re: [PATCH v2 2/5] pid: add pidfd_open()

On Sat, Mar 30, 2019 at 12:45:46AM +0100, Jann Horn wrote:
> On Fri, Mar 29, 2019 at 4:54 PM Christian Brauner <christian@...uner.io> wrote:
> > /* Introduction */
> > This adds the pidfd_open() syscall.
> > pidfd_open() allows to retrieve file descriptors for a given pid. This
> > includes both file descriptors for processes and file descriptors for
> > threads.
> 
> Looks good to me, overall. Apart from a few nits below:
> Reviewed-by: Jann Horn <jannh@...gle.com>

Thanks! Will fixup the nits and add your Reviewed-by!

> 
> [...]
> > diff --git a/kernel/pid.c b/kernel/pid.c
> > index 20881598bdfa..8c9e15e0e463 100644
> > --- a/kernel/pid.c
> > +++ b/kernel/pid.c
> [...]
> > +static struct file *pidfd_open_proc_pid(const struct file *procf, pid_t pid,
> > +                                       const struct pid *pidfd_pid)
> > +{
> > +       char name[12]; /* int to strlen + \0 but with */
> 
> nit: comment suddenly ends at "but with"?

Will fix.

> 
> [...]
> > +}
> > +
> > +static inline int pidfd_to_procfd(int procfd, struct file *pidfd_file)
> > +{
> > +       long fd;
> 
> nit: This should probably be an int?

Yes.

> 
> [...]
> > +       return fd;
> > +}
> [...]
> > +static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > +{
> > +       int procfd = arg;
> 
> nit: I think it'd be semantically cleaner to move this assignment into
> the switch case, but I don't feel about it strongly.

Agreed.

> 
> > +       switch (cmd) {
> > +       case PIDFD_GET_PROCFD:
> > +               return pidfd_to_procfd(procfd, file);
> > +       default:
> > +               return -ENOTTY;
> > +       }
> > +}