From: "Adrian Ratiu" <adrian.ratiu@collabora.com>
To: "Kees Cook" <keescook@chromium.org>
Cc: "Christian Brauner" <brauner@kernel.org>,
linux-fsdevel@vger.kernel.org, kernel@collabora.com,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
"Guenter Roeck" <groeck@chromium.org>,
"Doug Anderson" <dianders@chromium.org>,
"Jann Horn" <jannh@google.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Randy Dunlap" <rdunlap@infradead.org>,
"Mike Frysinger" <vapier@chromium.org>
Subject: Re: [PATCH v2] proc: allow restricting /proc/pid/mem writes
Date: Tue, 05 Mar 2024 19:34:34 +0000 [thread overview]
Message-ID: <45d98-65e77400-5-31aa8000@248840925> (raw)
In-Reply-To: <202403051033.9527DD75@keescook>
On Tuesday, March 05, 2024 20:37 EET, Kees Cook <keescook@chromium.org> wrote:
> On Tue, Mar 05, 2024 at 11:32:04AM +0100, Christian Brauner wrote:
> > On Tue, Mar 05, 2024 at 02:12:26AM -0800, Kees Cook wrote:
> > > On Tue, Mar 05, 2024 at 10:58:25AM +0100, Christian Brauner wrote:
> > > > Since the write handler for /proc/<pid>/mem does raise FOLL_FORCE
> > > > unconditionally it likely would implicitly. But I'm not familiar enough
> > > > with FOLL_FORCE to say for sure.
> > >
> > > I should phrase the question better. :) Is the supervisor writing into
> > > read-only regions of the child process?
> >
> > Hm... I suspect we don't. Let's take two concrete examples so you can
> > tell me.
> >
> > Incus intercepts the sysinfo() syscall. It prepares a struct sysinfo
> > with cgroup aware values for the supervised process and then does:
> >
> > unix.Pwrite(siov.memFd, &sysinfo, sizeof(struct sysinfo), seccomp_data.args[0]))
> >
> > It also intercepts some bpf system calls attaching bpf programs for the
> > caller. If that fails we update the log buffer for the supervised
> > process:
> >
> > union bpf_attr attr = {}, new_attr = {};
> >
> > // read struct bpf_attr from mem_fd
> > ret = pread(mem_fd, &attr, attr_len, req->data.args[1]);
> > if (ret < 0)
> > return -errno;
> >
> > // Do stuff with attr. Stuff fails. Update log buffer for supervised process:
> > if ((new_attr.log_size) > 0 && (pwrite(mem_fd, new_attr.log_buf, new_attr.log_size, attr.log_buf) != new_attr.log_size))
>
> This is almost certainly in writable memory (either stack or .data).
Mostly yes, but we can't be certain where it comes from, because
SECCOMP_IOCTL_NOTIF_RECV passes any addresses set by the
caller to the supervisor process.
It is a kind of "implementation defined" behavior, just like we
can't predict what the supervisor will do with the caller mem :)
>
> > But I'm not sure if there are other use-cases that would require this.
>
> Maybe this option needs to be per-process (like no_new_privs), and with
> a few access levels:
>
> - as things are now
> - no FOLL_FORCE unless by ptracer
> - no writes unless by ptracer
> - no FOLL_FORCE ever
> - no writes ever
> - no reads unless by ptracer
> - no reads ever
>
> Which feels more like 3 toggles: read, write, FOLL_FORCE. Each set to
> "DAC", "ptracer", and "none"?
I really like this approach because it provides a mechanism
with maximum flexibility without imposing a specific policy.
What does DAC mean in this context? My mind jumps to
Digital to Analog Converter :)
Shall I give it a try in v3?
>
> --
> Kees Cook
next prev parent reply other threads:[~2024-03-05 19:34 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-01 21:34 [PATCH v2] proc: allow restricting /proc/pid/mem writes Adrian Ratiu
2024-03-01 23:55 ` Kees Cook
2024-03-02 10:31 ` Adrian Ratiu
2024-03-04 14:06 ` Adrian Ratiu
2024-03-04 17:42 ` Kees Cook
2024-03-04 13:20 ` Christian Brauner
2024-03-04 13:48 ` Adrian Ratiu
2024-03-04 14:05 ` Christian Brauner
2024-03-04 14:35 ` Adrian Ratiu
2024-03-04 17:56 ` Kees Cook
2024-03-04 17:49 ` Kees Cook
2024-03-05 8:59 ` Christian Brauner
2024-03-05 9:41 ` Kees Cook
2024-03-05 9:58 ` Christian Brauner
2024-03-05 10:12 ` Kees Cook
2024-03-05 10:32 ` Christian Brauner
2024-03-05 18:37 ` Kees Cook
2024-03-05 19:34 ` Adrian Ratiu [this message]
2024-03-05 19:38 ` Kees Cook
2024-03-06 10:31 ` Christian Brauner
2024-03-05 11:03 ` Christian Brauner
2024-03-05 18:33 ` Kees Cook
2024-03-06 10:49 ` Matt Denton
2024-03-05 15:38 ` Adrian Ratiu
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