From: Christian Brauner <christian.brauner@ubuntu.com>
To: Jann Horn <jannh@google.com>
Cc: Christian Kellner <ckellner@redhat.com>,
Christian Brauner <christian@brauner.io>,
kernel list <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Christian Kellner <christian@kellner.me>,
Andrew Morton <akpm@linux-foundation.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>, Michal Hocko <mhocko@suse.com>,
Thomas Gleixner <tglx@linutronix.de>,
Elena Reshetova <elena.reshetova@intel.com>,
Roman Gushchin <guro@fb.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Aleksa Sarai <cyphar@cyphar.com>,
"Dmitry V. Levin" <ldv@altlinux.org>
Subject: Re: [PATCH v3 1/2] pidfd: show pids for nested pid namespaces in fdinfo
Date: Fri, 11 Oct 2019 17:17:01 +0200 [thread overview]
Message-ID: <20191011151700.hdvztoxonpvogadv@wittgenstein> (raw)
In-Reply-To: <CAG48ez1xNonmxwa3DRD44WJiComOHRxdHud5+LWea3OXzr4hkg@mail.gmail.com>
On Fri, Oct 11, 2019 at 04:55:59PM +0200, Jann Horn wrote:
> On Fri, Oct 11, 2019 at 2:23 PM Christian Kellner <ckellner@redhat.com> wrote:
> > The fdinfo file for a process file descriptor already contains the
> > pid of the process in the callers namespaces. Additionally, if pid
> > namespaces are configured, show the process ids of the process in
> > all nested namespaces in the same format as in the procfs status
> > file, i.e. "NSPid:\t%d\%d...". This allows the easy identification
> > of the processes in nested namespaces.
> [...]
> > #ifdef CONFIG_PROC_FS
> > +static inline void print_pidfd_nspid(struct seq_file *m, struct pid *pid,
> > + struct pid_namespace *ns)
>
> `ns` is the namespace of the PID namespace of the procfs instance
> through which the file descriptor is being viewed.
>
> > +{
> > +#ifdef CONFIG_PID_NS
> > + int i;
> > +
> > + seq_puts(m, "\nNSpid:");
> > + for (i = ns->level; i <= pid->level; i++) {
>
> ns->level is the level of the PID namespace associated with the procfs
> instance through which the file descriptor is being viewed. pid->level
> is the level of the PID associated with the pidfd.
>
> > + ns = pid->numbers[i].ns;
> > + seq_put_decimal_ull(m, "\t", pid_nr_ns(pid, ns));
> > + }
> > +#endif
> > +}
>
> I think you assumed that `ns` is always going to contain `pid`.
> However, that's not the case. Consider the following scenario:
>
> - the init_pid_ns has two child PID namespaces, A and B (each with
> its own mount namespace and procfs instance)
> - process P1 lives in A
> - process P2 lives in B
> - P1 opens a pidfd for itself
> - P1 passes the pidfd to P2 (e.g. via a unix domain socket)
> - P2 reads /proc/self/fdinfo/$pidfd
>
> Now the loop will print the ID of P1 in A. I don't think that's what
> you intended? You might want to bail out if "pid_nr_ns(pid, ns) == 0",
> or something like that.
I assumed the same thing happens when you pass around an fd for
/proc/self/status and that's why I didn't object to this behavior.
Christian
next prev parent reply other threads:[~2019-10-11 15:17 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-08 13:36 [PATCH] pidfd: show pids for nested pid namespaces in fdinfo Christian Kellner
2019-10-08 13:52 ` Christian Brauner
2019-10-08 14:00 ` Michal Hocko
2019-10-09 16:05 ` [PATCH v2 1/2] " Christian Kellner
2019-10-09 16:05 ` [PATCH v2 2/2] pidfd: add tests for NSpid info " Christian Kellner
2019-10-11 15:09 ` Jann Horn
2019-10-11 17:08 ` Christian Brauner
2019-10-09 17:29 ` [PATCH v2 1/2] pidfd: show pids for nested pid namespaces " Christian Brauner
2019-10-11 12:23 ` [PATCH v3 " Christian Kellner
2019-10-11 12:23 ` [PATCH v3 2/2] pidfd: add tests for NSpid info " Christian Kellner
2019-10-11 13:18 ` Christian Brauner
2019-10-11 13:17 ` [PATCH v3 1/2] pidfd: show pids for nested pid namespaces " Christian Brauner
2019-10-11 14:55 ` Jann Horn
2019-10-11 15:17 ` Christian Brauner [this message]
2019-10-11 15:30 ` Jann Horn
2019-10-11 16:58 ` Christian Brauner
2019-10-11 18:20 ` Jann Horn
2019-10-12 10:19 ` [PATCH] pidfd: add NSpid entries to fdinfo Christian Brauner
2019-10-12 10:21 ` Christian Brauner
2019-10-14 9:43 ` Christian Kellner
2019-10-14 10:31 ` Christian Brauner
2019-10-14 15:10 ` Jann Horn
2019-10-14 15:20 ` Christian Kellner
2019-10-14 15:09 ` Jann Horn
2019-10-14 17:06 ` Christian Brauner
2019-10-14 16:20 ` [PATCH v4 1/2] " Christian Kellner
2019-10-14 16:20 ` [PATCH v4 2/2] pidfd: add tests for NSpid info in fdinfo Christian Kellner
2019-10-15 10:07 ` Christian Brauner
2019-11-13 11:52 ` Naresh Kamboju
2019-11-13 12:20 ` Christian Brauner
2019-10-15 9:40 ` [PATCH v4 1/2] pidfd: add NSpid entries to fdinfo Christian Brauner
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