From: Christian Brauner <brauner@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Tycho Andersen <tycho@tycho.pizza>,
linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect PIDFD_THREAD
Date: Tue, 20 Feb 2024 13:59:56 +0100 [thread overview]
Message-ID: <20240220-anlegen-feinmechaniker-3c2cfcc3ec01@brauner> (raw)
In-Reply-To: <20240220110012.GB7783@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 2610 bytes --]
On Tue, Feb 20, 2024 at 12:00:12PM +0100, Oleg Nesterov wrote:
> On 02/20, Christian Brauner wrote:
> >
> > On Tue, Feb 20, 2024 at 10:02:56AM +0100, Oleg Nesterov wrote:
> > >
> > > Ah. IIRC criu uses this hack to restore the pending (arbitrary) signals
> > > collected at dump time.
> > >
> > > I was a bit surprise sys_pidfd_send_signal() allows this hack too, I don't
> >
> > I think that we simply mirrored the restrictions in the other system
> > calls.
> >
> > > think that criu uses pidfd at restore time, but I do not know.
> >
> > Hm, I just checked and it doesn't use pidfd_send_signal(). It uses
> > pidfds but only for pid reuse detection for RPC clients.
>
> But perhaps something else already uses pidfd_send_signal() with info != NULL
> or with info->si_code == SI_USER, we can't know. Please see below.
>
> > So right now si_code is blocked for >= 0 and for SI_TKILL. If we were to
> > simply ensure that si_code can't be < 0 then this amounts to effectively
> > blocking @info from being filled in by userspace at all. Because 0 is a
> > valid value.
>
> I'am afraid I misunderstand you again... 0 == SI_USER is not a valid value
> when siginfo != NULL.
Yes, I know. We're on the same page. I would just have preferred to
restrict remulating si_code completely because we don't know whether
that's actually used for pidfd_send_signal(). The point I was trying to
make is that si_code has no value that means "unset" so restricting
si_code further means always rejecting @info when it's passed.
>
> Perhaps we can kill the "task_pid(current) != pid" check and just return
> EPERM if "kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL", I don't think
> anobody needs pidfd_send_send_signal() to signal yourself. See below.
Yeah.
>
> > + /* Currently unused. */
> > + if (info)
> > + return -EINVAL;
>
> Well, to me this looks like the unnecessary restriction... And why?
Because right now we aren't sure that it's used and we aren't sure what
use-cases are there.
>
> But whatever we do,
>
> > - /* Only allow sending arbitrary signals to yourself. */
> > - ret = -EPERM;
> > - if ((task_pid(current) != pid) &&
> > - (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
> > - goto err;
>
> Can I suggest to fix this check in your tree (add type > PIDTYPE_TGID as
> we discussed) first, then do other changes on top?
Yes, absolutely. That was always the plan. See appended patch I put on top.
I put you as author since you did spot this. Let me know if you don't
want that.
[-- Attachment #2: 0001-signal-adjust-si_code-restriction-in-pidfd_send_sign.patch --]
[-- Type: text/x-diff, Size: 1207 bytes --]
From 67a1a77630c00f457a46e1164caf0d32c0edc127 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 20 Feb 2024 13:53:00 +0100
Subject: [PATCH] signal: adjust si_code restriction in pidfd_send_signal()
Since we now allow specifying PIDFD_SEND_PROCESS_GROUP for
pidfd_send_signal() to send signals to process groups we need to adjust
the check restricting si_code emulation by userspace to account for
PIDTYPE_PGID.
Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20240214123655.GB16265@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
kernel/signal.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index cf6539a6b1cb..5f5620c81d3a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3956,7 +3956,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
/* Only allow sending arbitrary signals to yourself. */
ret = -EPERM;
- if ((task_pid(current) != pid) &&
+ if (((task_pid(current) != pid) || type > PIDTYPE_TGID) &&
(kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
goto err;
} else {
--
2.43.0
next prev parent reply other threads:[~2024-02-20 13:00 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-09 13:06 [PATCH v2 1/2] signal: add the "int si_code" arg to prepare_kill_siginfo() Oleg Nesterov
2024-02-09 13:06 ` [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect PIDFD_THREAD Oleg Nesterov
2024-02-09 15:11 ` Christian Brauner
2024-02-09 15:15 ` Christian Brauner
2024-02-09 15:43 ` Oleg Nesterov
2024-02-09 15:49 ` Christian Brauner
2024-02-09 15:56 ` Oleg Nesterov
2024-02-10 10:23 ` Christian Brauner
2024-02-10 12:30 ` Oleg Nesterov
2024-02-10 12:47 ` Oleg Nesterov
2024-02-10 12:54 ` Christian Brauner
2024-02-10 13:15 ` Oleg Nesterov
2024-02-10 14:26 ` Christian Brauner
2024-02-10 16:51 ` Oleg Nesterov
2024-02-10 17:22 ` Christian Brauner
2024-02-14 12:36 ` Oleg Nesterov
2024-02-16 12:28 ` Christian Brauner
2024-02-16 13:06 ` Oleg Nesterov
2024-02-16 14:46 ` Christian Brauner
2024-02-16 18:12 ` Oleg Nesterov
2024-02-20 8:34 ` Christian Brauner
2024-02-20 9:02 ` Oleg Nesterov
2024-02-20 9:22 ` Christian Brauner
2024-02-20 11:00 ` Oleg Nesterov
2024-02-20 12:59 ` Christian Brauner [this message]
2024-02-20 16:22 ` Oleg Nesterov
2024-02-21 7:42 ` Christian Brauner
2024-02-21 12:55 ` Oleg Nesterov
2024-02-21 13:35 ` Christian Brauner
2024-02-09 19:08 ` Tycho Andersen
2024-02-09 15:10 ` [PATCH v2 1/2] signal: add the "int si_code" arg to prepare_kill_siginfo() Christian Brauner
2024-02-09 16:13 ` Christian Brauner
2024-02-09 16:22 ` Eric W. Biederman
2024-02-09 16:39 ` Oleg Nesterov
2024-02-09 19:36 ` Christian Brauner
2024-02-09 19:53 ` Oleg Nesterov
2024-02-09 20:01 ` Tycho Andersen
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