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From: Kees Cook <keescook@chromium.org>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: luto@amacapital.net, jannh@google.com, wad@chromium.org,
	shuah@kernel.org, ast@kernel.org, daniel@iogearbox.net,
	kafai@fb.com, songliubraving@fb.com, yhs@fb.com,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	Tycho Andersen <tycho@tycho.ws>,
	Tyler Hicks <tyhicks@canonical.com>
Subject: Re: [PATCH v2 1/3] seccomp: add SECCOMP_USER_NOTIF_FLAG_CONTINUE
Date: Thu, 10 Oct 2019 14:45:38 -0700	[thread overview]
Message-ID: <201910101440.17A13952@keescook> (raw)
In-Reply-To: <20190920083007.11475-2-christian.brauner@ubuntu.com>

On Fri, Sep 20, 2019 at 10:30:05AM +0200, Christian Brauner wrote:
> + * Similar precautions should be applied when stacking SECCOMP_RET_USER_NOTIF.
> + * For SECCOMP_RET_USER_NOTIF filters acting on the same syscall the uppermost
> + * filter takes precedence. This means that the uppermost
> + * SECCOMP_RET_USER_NOTIF filter can override any SECCOMP_IOCTL_NOTIF_SEND from
> + * lower filters essentially allowing all syscalls to pass by using
> + * SECCOMP_USER_NOTIF_FLAG_CONTINUE. Note that SECCOMP_RET_USER_NOTIF can
                                                          ^^^^^^^^^^^^^^
This is meant to read RET_TRACE, yes?

> + * equally be overriden by SECCOMP_USER_NOTIF_FLAG_CONTINUE.

I rewrote this paragraph with that corrected and swapping some
"upper/lower" to "most recently added" etc:

+ * Similar precautions should be applied when stacking SECCOMP_RET_USER_NOTIF
+ * or SECCOMP_RET_TRACE. For SECCOMP_RET_USER_NOTIF filters acting on the
+ * same syscall, the most recently added filter takes precedence. This means
+ * that the new SECCOMP_RET_USER_NOTIF filter can override any
+ * SECCOMP_IOCTL_NOTIF_SEND from earlier filters, essentially allowing all
+ * such filtered syscalls to be executed by sending the response
+ * SECCOMP_USER_NOTIF_FLAG_CONTINUE. Note that SECCOMP_RET_TRACE can equally
+ * be overriden by SECCOMP_USER_NOTIF_FLAG_CONTINUE.


Ultimately, I think this caveat is fine. RET_USER_NOTIF and RET_TRACE are
both used from the "process manager" use-case. The benefits of "continue"
semantics here outweighs the RET_USER_NOTIF and RET_TRACE "bypass". If
we end up in a situation where we need to deal with some kind of
nesting where this is a problem in practice, we can revisit this.

Applied to my for-next/seccomp. Thanks!

-- 
Kees Cook

  reply	other threads:[~2019-10-10 21:45 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-20  8:30 [PATCH v2 0/3] seccomp: continue syscall from notifier Christian Brauner
2019-09-20  8:30 ` [PATCH v2 1/3] seccomp: add SECCOMP_USER_NOTIF_FLAG_CONTINUE Christian Brauner
2019-10-10 21:45   ` Kees Cook [this message]
2019-10-11  9:46     ` Christian Brauner
2019-09-20  8:30 ` [PATCH v2 2/3] seccomp: avoid overflow in implicit constant conversion Christian Brauner
2019-09-20  8:47   ` Tycho Andersen
2019-09-20  8:30 ` [PATCH v2 3/3] seccomp: test SECCOMP_USER_NOTIF_FLAG_CONTINUE Christian Brauner

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