From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C208DC2D0EB for ; Sun, 29 Mar 2020 00:15:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A232320732 for ; Sun, 29 Mar 2020 00:15:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727729AbgC2APZ (ORCPT ); Sat, 28 Mar 2020 20:15:25 -0400 Received: from www62.your-server.de ([213.133.104.62]:58768 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726604AbgC2APZ (ORCPT ); Sat, 28 Mar 2020 20:15:25 -0400 Received: from sslproxy05.your-server.de ([78.46.172.2]) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1jILbm-0005Oc-Ov; Sun, 29 Mar 2020 01:15:22 +0100 Received: from [178.195.186.98] (helo=pc-9.home) by sslproxy05.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jILbm-000IV8-Bo; Sun, 29 Mar 2020 01:15:22 +0100 Subject: Re: [PATCH bpf-next v8 0/8] MAC and Audit policy using eBPF (KRSI) To: KP Singh Cc: Kees Cook , open list , bpf , Linux Security Module list , Alexei Starovoitov , James Morris , Paul Turner , Jann Horn , Florent Revest , Brendan Jackman , Greg Kroah-Hartman References: <20200327192854.31150-1-kpsingh@chromium.org> <4e5a09bb-04c4-39b8-10d4-59496ffb5eee@iogearbox.net> <20200328195636.GA95544@google.com> <202003281449.333BDAF6@keescook> <20200329000738.GA230422@google.com> From: Daniel Borkmann Message-ID: Date: Sun, 29 Mar 2020 01:15:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20200329000738.GA230422@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.2/25765/Sat Mar 28 14:16:42 2020) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/29/20 1:07 AM, KP Singh wrote: > On 28-Mar 23:30, KP Singh wrote: >> On Sat, Mar 28, 2020 at 10:50 PM Kees Cook wrote: >>> >>> On Sat, Mar 28, 2020 at 08:56:36PM +0100, KP Singh wrote: >>>> Since the attachment succeeds and the hook does not get called, it >>>> seems like "bpf" LSM is not being initialized and the hook, although >>>> present, does not get called. >>>> >>>> This indicates that "bpf" is not in CONFIG_LSM. It should, however, be >>>> there by default as we added it to default value of CONFIG_LSM and >>>> also for other DEFAULT_SECURITY_* options. >>>> >>>> Let me know if that's the case and it fixes it. >>> >>> Is the selftest expected to at least fail cleanly (i.e. not segfault) >> >> I am not sure where the crash comes from, it does not look like it's test_lsm, >> it seems to happen in test_overhead. Both seem to run fine for me. > > So I was able to reproduce the crash: > > * Remove "bpf" from CONFIG_LSM > > ./test_progs -n 66,67 > test_test_lsm:PASS:skel_load 0 nsec > test_test_lsm:PASS:attach 0 nsec > test_test_lsm:PASS:exec_cmd 0 nsec > test_test_lsm:FAIL:bprm_count bprm_count = 0 > test_test_lsm:FAIL:heap_mprotect want errno=EPERM, got 0 > #66 test_lsm:FAIL > Caught signal #11! > Stack trace: > ./test_progs(crash_handler+0x1f)[0x55b7f9867acf] > /lib/x86_64-linux-gnu/libpthread.so.0(+0x13520)[0x7fcf1467e520] > /lib/x86_64-linux-gnu/libc.so.6(+0x15f73d)[0x7fcf1460a73d] > /lib/x86_64-linux-gnu/libc.so.6(__libc_calloc+0x2ca)[0x7fcf1453286a] > /usr/lib/x86_64-linux-gnu/libelf.so.1(+0x37 > > [snip] > > * The crash went away when I removed the heap_mprotect call, now the BPF > hook attached did not allow this operation, so it had no side-effects. > Which lead me to believe the crash could be a side-effect of this > operation. So I did: > > --- a/tools/testing/selftests/bpf/prog_tests/test_lsm.c > +++ b/tools/testing/selftests/bpf/prog_tests/test_lsm.c > @@ -29,7 +29,7 @@ int heap_mprotect(void) > if (buf == NULL) > return -ENOMEM; > > - ret = mprotect(buf, sz, PROT_READ | PROT_EXEC); > + ret = mprotect(buf, sz, PROT_READ | PROT_WRITE | PROT_EXEC); > free(buf); > return ret; > } > > and the crash went away. Which made me realize that the free > operation does not like memory without PROT_WRITE, So I did this: > > diff --git a/tools/testing/selftests/bpf/prog_tests/test_lsm.c b/tools/testing/selftests/bpf/prog_tests/test_lsm.c > index fcd839e88540..78f125cc09b3 100644 > --- a/tools/testing/selftests/bpf/prog_tests/test_lsm.c > +++ b/tools/testing/selftests/bpf/prog_tests/test_lsm.c > @@ -30,7 +30,7 @@ int heap_mprotect(void) > return -ENOMEM; > > ret = mprotect(buf, sz, PROT_READ | PROT_EXEC); > - free(buf); > + // free(buf); > return ret; > } > > and the crash went away as well. So it indeed was a combination of: > > * CONFIG_LSM not enabling the hook > * mprotect marking the memory as non-writeable > * free being called on the memory. > > I will send a v9 which has the PROT_WRITE on the mprotect. Thanks > for noticing this! And also explains the stack trace for __libc_calloc() where it's trying to zero the area later on. Thanks for the quick debugging, Daniel