From: Christian Brauner <christian@brauner.io>
To: Jonathan Kowalski <bl0pbl33p@gmail.com>
Cc: Jann Horn <jannh@google.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Andy Lutomirski <luto@kernel.org>,
David Howells <dhowells@redhat.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Linux API <linux-api@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Kees Cook <keescook@chromium.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
"Dmitry V. Levin" <ldv@altlinux.org>,
Andrew Morton <akpm@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>,
Aleksa Sarai <cyphar@cyphar.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Joel Fernandes <joel@joelfernandes.org>,
Daniel Colascione <dancol@google.com>
Subject: Re: [PATCH 3/4] signal: support pidctl() with pidfd_send_signal()
Date: Mon, 25 Mar 2019 21:05:54 +0100 [thread overview]
Message-ID: <20190325200552.fs4exsj3fsls7adu@brauner.io> (raw)
In-Reply-To: <CAGLj2rGTK2xLhDhBjh1wSpAiuxbLBt-AwREB5kA8LeW4JFzgsg@mail.gmail.com>
On Mon, Mar 25, 2019 at 06:28:53PM +0000, Jonathan Kowalski wrote:
> On Mon, Mar 25, 2019 at 4:21 PM Christian Brauner <christian@brauner.io> wrote:
> >
> > Let pidfd_send_signal() use pidfds retrieved via pidctl(). With this patch
> > pidfd_send_signal() becomes independent of procfs. This fullfils the
> > request made when we merged the pidfd_send_signal() patchset. The
> > pidfd_send_signal() syscall is now always available allowing for it to be
> > used by users without procfs mounted or even users without procfs support
> > compiled into the kernel.
> >
> > Signed-off-by: Christian Brauner <christian@brauner.io>
> > Reviewed-by: David Howells <dhowells@redhat.com>
> > Acked-by: Serge Hallyn <serge@hallyn.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Alexey Dobriyan <adobriyan@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Jann Horn <jannh@google.com
> > Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
> > Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > Cc: Jonathan Kowalski <bl0pbl33p@gmail.com>
> > Cc: "Dmitry V. Levin" <ldv@altlinux.org>
> > Cc: Andy Lutomirsky <luto@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Oleg Nesterov <oleg@redhat.com>
> > Cc: Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>
> > Cc: Aleksa Sarai <cyphar@cyphar.com>
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > ---
> > kernel/signal.c | 20 +++++++++-----------
> > kernel/sys_ni.c | 3 ---
> > 2 files changed, 9 insertions(+), 14 deletions(-)
> >
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index b7953934aa99..d77183be1677 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -3513,7 +3513,6 @@ SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)
> > return kill_something_info(sig, &info, pid);
> > }
> >
> > -#ifdef CONFIG_PROC_FS
> > /*
> > * Verify that the signaler and signalee either are in the same pid namespace
> > * or that the signaler's pid namespace is an ancestor of the signalee's pid
> > @@ -3521,16 +3520,13 @@ SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)
> > */
> > static bool access_pidfd_pidns(struct pid *pid)
>
> If it is agreed upon to remove the ability of using /proc/<PID> as a
> pidfd pidfd_send_signal accepts, is lifting this check acceptable?
>
> The system call as is does not allow for a process to acquire a pidfd
> without being in an ancestor namespace or the same namespace. Thus,
> there are good reasons to allow for this to work and be able to work
> around the limitations imposed by pid namespaces if userspace
> explicitly decides to do so, by passing around the pidfd to some other
> process.
The original problem with this was - I think - that we hadn't settled
what certain values in struct siginfo_t should be set to when signaling
e.g. into ancestor pid namespaces. And if we did, we need to hook into
a widely used function in the kernel (I don't have the appropriate
thread handy atm) and we decided to punt on this until userspace really
needs this feature.
>
> Also, you would need to translate this only once, when filling in the
> structure. The other process is bound to its pid ns as long as it is
> alive, therefore it would be simple without having to do anything
> fancy at read side (unlike unix sockets).
>
> > {
> > + int ret;
> > struct pid_namespace *active = task_active_pid_ns(current);
> > struct pid_namespace *p = ns_of_pid(pid);
> >
> > - for (;;) {
> > - if (!p)
> > - return false;
> > - if (p == active)
> > - break;
> > - p = p->parent;
> > - }
> > + ret = pidnscmp(active, p);
> > + if (ret < 0)
> > + return false;
> >
> > return true;
> > }
> > @@ -3581,12 +3577,15 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
> > if (flags)
> > return -EINVAL;
> >
> > - f = fdget_raw(pidfd);
> > + f = fdget(pidfd);
> > if (!f.file)
> > return -EBADF;
> >
> > /* Is this a pidfd? */
> > - pid = tgid_pidfd_to_pid(f.file);
> > + if (f.file->f_op == &pidfd_fops)
> > + pid = f.file->private_data;
> > + else
> > + pid = tgid_pidfd_to_pid(f.file);
> > if (IS_ERR(pid)) {
> > ret = PTR_ERR(pid);
> > goto err;
> > @@ -3625,7 +3624,6 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
> > fdput(f);
> > return ret;
> > }
> > -#endif /* CONFIG_PROC_FS */
> >
> > static int
> > do_send_specific(pid_t tgid, pid_t pid, int sig, struct kernel_siginfo *info)
> > diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> > index d21f4befaea4..4d9ae5ea6caf 100644
> > --- a/kernel/sys_ni.c
> > +++ b/kernel/sys_ni.c
> > @@ -167,9 +167,6 @@ COND_SYSCALL(syslog);
> >
> > /* kernel/sched/core.c */
> >
> > -/* kernel/signal.c */
> > -COND_SYSCALL(pidfd_send_signal);
> > -
> > /* kernel/sys.c */
> > COND_SYSCALL(setregid);
> > COND_SYSCALL(setgid);
> > --
> > 2.21.0
> >
next prev parent reply other threads:[~2019-03-25 20:06 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-25 16:20 [PATCH 0/4] pid: add pidctl() Christian Brauner
2019-03-25 16:20 ` [PATCH 1/4] Make anon_inodes unconditional Christian Brauner
2019-03-25 16:20 ` [PATCH 2/4] pid: add pidctl() Christian Brauner
2019-03-25 17:20 ` Mika Penttilä
2019-03-25 19:59 ` Christian Brauner
2019-03-25 18:18 ` Jann Horn
2019-03-25 19:58 ` Christian Brauner
2019-03-26 16:07 ` Joel Fernandes
2019-03-26 16:15 ` Christian Brauner
2019-03-25 16:20 ` [PATCH 3/4] signal: support pidctl() with pidfd_send_signal() Christian Brauner
2019-03-25 18:28 ` Jonathan Kowalski
2019-03-25 20:05 ` Christian Brauner [this message]
2019-03-25 18:39 ` Jann Horn
2019-03-25 19:41 ` Christian Brauner
2019-03-25 16:20 ` [PATCH 4/4] tests: add pidctl() tests Christian Brauner
2019-03-25 16:48 ` [PATCH 0/4] pid: add pidctl() Daniel Colascione
2019-03-25 17:05 ` Konstantin Khlebnikov
2019-03-25 17:07 ` Daniel Colascione
2019-03-25 17:36 ` Joel Fernandes
2019-03-25 17:53 ` Daniel Colascione
2019-03-25 18:19 ` Jonathan Kowalski
2019-03-25 18:57 ` Daniel Colascione
2019-03-25 19:42 ` Jonathan Kowalski
2019-03-25 20:14 ` Daniel Colascione
2019-03-25 20:34 ` Jann Horn
2019-03-25 20:40 ` Jonathan Kowalski
2019-03-25 21:14 ` Jonathan Kowalski
2019-03-25 21:15 ` Jann Horn
2019-03-25 20:40 ` Christian Brauner
2019-03-25 20:15 ` Christian Brauner
2019-03-25 21:11 ` Joel Fernandes
2019-03-25 21:17 ` Daniel Colascione
2019-03-25 21:19 ` Jann Horn
2019-03-25 21:43 ` Joel Fernandes
2019-03-25 21:54 ` Jonathan Kowalski
2019-03-25 22:07 ` Daniel Colascione
2019-03-25 22:37 ` Jonathan Kowalski
2019-03-25 23:14 ` Daniel Colascione
2019-03-26 3:03 ` Joel Fernandes
2019-03-25 16:56 ` David Howells
2019-03-25 16:58 ` Daniel Colascione
2019-03-25 23:39 ` Andy Lutomirski
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