linux-kernel - Re: security problem with seccomp-filter

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Message-ID: <20150412213311.GA16854@qarx.de>
Date:	Sun, 12 Apr 2015 23:33:12 +0200
From:	Felix von Leitner <felix-linuxkernel@...e.de>
To:	Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>
Subject: Re: security problem with seccomp-filter

> What you're describing should work correctly (it's part of the
> regression test suite we use). So, given that, I'd love to get to the
> bottom of what you're seeing. Do you have a URL to your code? What
> architecture are you running on?

Well, I must be doing something wrong then.
I extracted a test case from my program.
I put it on http://ptrace.fefe.de/seccompfail.c

It installs three seccomp filters, the last one containing this:

    DISALLOW_SYSCALL(prctl),

with

#define DISALLOW_SYSCALL(name) \
	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_##name, 0, 1), \
	BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)

It is my understanding that that should then kill the process if the
prctl syscall is called again.

I test this by attempting to install the very same seccomp filter again,
which calls prctl, but the process is not killed.

What am I doing wrong?

Thanks,
Felix

View attachment "seccompfail.c" of type "text/x-csrc" (6335 bytes)