| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <e8a118dc-6b10-fefd-a9e1-75367f9b74a5@iogearbox.net>
Date: Fri, 28 May 2021 13:54:54 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Jiri Olsa <jolsa@...hat.com>
Cc: Paul Moore <paul@...l-moore.com>,
Ondrej Mosnacek <omosnace@...hat.com>,
linux-security-module@...r.kernel.org,
James Morris <jmorris@...ei.org>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Stephen Smalley <stephen.smalley.work@...il.com>,
selinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-fsdevel@...r.kernel.org, bpf@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Casey Schaufler <casey@...aufler-ca.com>,
andrii.nakryiko@...il.com
Subject: Re: [PATCH v2] lockdown,selinux: avoid bogus SELinux lockdown
permission checks
On 5/28/21 1:47 PM, Jiri Olsa wrote:
> On Fri, May 28, 2021 at 11:56:02AM +0200, Daniel Borkmann wrote:
>
>> Ondrej / Paul / Jiri: at least for the BPF tracing case specifically (I haven't looked
>> at the rest but it's also kind of independent), the attached fix should address both
>> reported issues, please take a look & test.
>>
>> Thanks a lot,
>> Daniel
>
>> From 5893ad528dc0a0a68933b8f2a81b18d3f539660d Mon Sep 17 00:00:00 2001
>> From: Daniel Borkmann <daniel@...earbox.net>
>> Date: Fri, 28 May 2021 09:16:31 +0000
>> Subject: [PATCH bpf] bpf, audit, lockdown: Fix bogus SELinux lockdown permission checks
>>
>> Commit 59438b46471a ("security,lockdown,selinux: implement SELinux lockdown")
>> added an implementation of the locked_down LSM hook to SELinux, with the aim
>> to restrict which domains are allowed to perform operations that would breach
>> lockdown. This is indirectly also getting audit subsystem involved to report
>> events. The latter is problematic, as reported by Ondrej and Serhei, since it
>> can bring down the whole system via audit:
>>
>> i) The audit events that are triggered due to calls to security_locked_down()
>> can OOM kill a machine, see below details [0].
>>
>> ii) It seems to be causing a deadlock via slow_avc_audit() -> audit_log_end()
>> when presumingly trying to wake up kauditd [1].
>>
>> Fix both at the same time by taking a completely different approach, that is,
>> move the check into the program verification phase where we actually retrieve
>> the func proto. This also reliably gets the task (current) that is trying to
>> install the tracing program, e.g. bpftrace/bcc/perf/systemtap/etc, and it also
>> fixes the OOM since we're moving this out of the BPF helpers which can be called
>> millions of times per second.
>>
>> [0] https://bugzilla.redhat.com/show_bug.cgi?id=1955585, Jakub Hrozek says:
>>
>> I starting seeing this with F-34. When I run a container that is traced with
>> BPF to record the syscalls it is doing, auditd is flooded with messages like:
>>
>> type=AVC msg=audit(1619784520.593:282387): avc: denied { confidentiality }
>> for pid=476 comm="auditd" lockdown_reason="use of bpf to read kernel RAM"
>> scontext=system_u:system_r:auditd_t:s0 tcontext=system_u:system_r:auditd_t:s0
>> tclass=lockdown permissive=0
>>
>> This seems to be leading to auditd running out of space in the backlog buffer
>> and eventually OOMs the machine.
>>
>> [...]
>> auditd running at 99% CPU presumably processing all the messages, eventually I get:
>> Apr 30 12:20:42 fedora kernel: audit: backlog limit exceeded
>> Apr 30 12:20:42 fedora kernel: audit: backlog limit exceeded
>> Apr 30 12:20:42 fedora kernel: audit: audit_backlog=2152579 > audit_backlog_limit=64
>> Apr 30 12:20:42 fedora kernel: audit: audit_backlog=2152626 > audit_backlog_limit=64
>> Apr 30 12:20:42 fedora kernel: audit: audit_backlog=2152694 > audit_backlog_limit=64
>> Apr 30 12:20:42 fedora kernel: audit: audit_lost=6878426 audit_rate_limit=0 audit_backlog_limit=64
>> Apr 30 12:20:45 fedora kernel: oci-seccomp-bpf invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0, oom_score_adj=-1000
>> Apr 30 12:20:45 fedora kernel: CPU: 0 PID: 13284 Comm: oci-seccomp-bpf Not tainted 5.11.12-300.fc34.x86_64 #1
>> Apr 30 12:20:45 fedora kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-2.fc32 04/01/2014
>> [...]
>>
>> [1] https://lore.kernel.org/linux-audit/CANYvDQN7H5tVp47fbYcRasv4XF07eUbsDwT_eDCHXJUj43J7jQ@mail.gmail.com/,
>> Serhei Makarov says:
>>
>> Upstream kernel 5.11.0-rc7 and later was found to deadlock during a
>> bpf_probe_read_compat() call within a sched_switch tracepoint. The problem
>> is reproducible with the reg_alloc3 testcase from SystemTap's BPF backend
>> testsuite on x86_64 as well as the runqlat,runqslower tools from bcc on
>> ppc64le. Example stack trace:
>>
>> [...]
>> [ 730.868702] stack backtrace:
>> [ 730.869590] CPU: 1 PID: 701 Comm: in:imjournal Not tainted, 5.12.0-0.rc2.20210309git144c79ef3353.166.fc35.x86_64 #1
>> [ 730.871605] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
>> [ 730.873278] Call Trace:
>> [ 730.873770] dump_stack+0x7f/0xa1
>> [ 730.874433] check_noncircular+0xdf/0x100
>> [ 730.875232] __lock_acquire+0x1202/0x1e10
>> [ 730.876031] ? __lock_acquire+0xfc0/0x1e10
>> [ 730.876844] lock_acquire+0xc2/0x3a0
>> [ 730.877551] ? __wake_up_common_lock+0x52/0x90
>> [ 730.878434] ? lock_acquire+0xc2/0x3a0
>> [ 730.879186] ? lock_is_held_type+0xa7/0x120
>> [ 730.880044] ? skb_queue_tail+0x1b/0x50
>> [ 730.880800] _raw_spin_lock_irqsave+0x4d/0x90
>> [ 730.881656] ? __wake_up_common_lock+0x52/0x90
>> [ 730.882532] __wake_up_common_lock+0x52/0x90
>> [ 730.883375] audit_log_end+0x5b/0x100
>> [ 730.884104] slow_avc_audit+0x69/0x90
>> [ 730.884836] avc_has_perm+0x8b/0xb0
>> [ 730.885532] selinux_lockdown+0xa5/0xd0
>> [ 730.886297] security_locked_down+0x20/0x40
>> [ 730.887133] bpf_probe_read_compat+0x66/0xd0
>> [ 730.887983] bpf_prog_250599c5469ac7b5+0x10f/0x820
>> [ 730.888917] trace_call_bpf+0xe9/0x240
>> [ 730.889672] perf_trace_run_bpf_submit+0x4d/0xc0
>> [ 730.890579] perf_trace_sched_switch+0x142/0x180
>> [ 730.891485] ? __schedule+0x6d8/0xb20
>> [ 730.892209] __schedule+0x6d8/0xb20
>> [ 730.892899] schedule+0x5b/0xc0
>> [ 730.893522] exit_to_user_mode_prepare+0x11d/0x240
>> [ 730.894457] syscall_exit_to_user_mode+0x27/0x70
>> [ 730.895361] entry_SYSCALL_64_after_hwframe+0x44/0xae
>> [...]
>>
>> Fixes: 59438b46471a ("security,lockdown,selinux: implement SELinux lockdown")
>> Reported-by: Ondrej Mosnacek <omosnace@...hat.com>
>> Reported-by: Jakub Hrozek <jhrozek@...hat.com>
>> Reported-by: Serhei Makarov <smakarov@...hat.com>
>> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
>> Cc: Stephen Smalley <sds@...ho.nsa.gov>
>> Cc: Jerome Marchand <jmarchan@...hat.com>
>> Cc: Frank Eigler <fche@...hat.com>
>> Cc: Jiri Olsa <jolsa@...hat.com>
>> Cc: Paul Moore <paul@...l-moore.com>
>
> found the original server and reproduced.. this patch fixes it for me
>
> Tested-by: Jiri Olsa <jolsa@...hat.com>
Thanks Jiri! If Paul is fine with this as well, I can later route this fix via
bpf tree.
Best,
Daniel
Powered by blists - more mailing lists