linux-kernel - Re: [PATCH v2 3/4] seccomp: Audit attempts to modify the actions

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Date:   Thu, 3 May 2018 16:48:09 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Steve Grubb <sgrubb@...hat.com>,
        Tyler Hicks <tyhicks@...onical.com>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Eric Paris <eparis@...hat.com>,
        Jonathan Corbet <corbet@....net>, linux-audit@...hat.com,
        linux-security-module@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 3/4] seccomp: Audit attempts to modify the
 actions_logged sysctl

On Thu, May 3, 2018 at 4:42 PM, Steve Grubb <sgrubb@...hat.com> wrote:
> On Thursday, May 3, 2018 4:18:26 PM EDT Paul Moore wrote:
>> On Wed, May 2, 2018 at 2:18 PM, Steve Grubb <sgrubb@...hat.com> wrote:
>> > On Wednesday, May 2, 2018 11:53:19 AM EDT Tyler Hicks wrote:
>> >> The decision to log a seccomp action will always be subject to the
>> >> value of the kernel.seccomp.actions_logged sysctl, even for processes
>> >> that are being inspected via the audit subsystem, in an upcoming patch.
>> >> Therefore, we need to emit an audit record on attempts at writing to the
>> >> actions_logged sysctl when auditing is enabled.
>> >>
>> >> This patch updates the write handler for the actions_logged sysctl to
>> >> emit an audit record on attempts to write to the sysctl. Successful
>> >> writes to the sysctl will result in a record that includes a normalized
>> >> list of logged actions in the "actions" field and a "res" field equal to
>> >> 0. Unsuccessful writes to the sysctl will result in a record that
>> >> doesn't include the "actions" field and has a "res" field equal to 1.
>> >>
>> >> Not all unsuccessful writes to the sysctl are audited. For example, an
>> >> audit record will not be emitted if an unprivileged process attempts to
>> >> open the sysctl file for reading since that access control check is not
>> >> part of the sysctl's write handler.
>> >>
>> >> Below are some example audit records when writing various strings to the
>> >> actions_logged sysctl.
>> >>
>> >> Writing "not-a-real-action", when the kernel.seccomp.actions_logged
>> >> sysctl previously was "kill_process kill_thread trap errno trace log",
>> >>
>> >> emits this audit record:
>> >>  type=CONFIG_CHANGE msg=audit(1525275273.537:130): op=seccomp-logging
>> >>  old-actions=kill_process,kill_thread,trap,errno,trace,log res=0
>> >>
>> >> If you then write "kill_process kill_thread errno trace log", this audit
>> >>
>> >> record is emitted:
>> >>  type=CONFIG_CHANGE msg=audit(1525275310.208:136): op=seccomp-logging
>> >>  actions=kill_process,kill_thread,errno,trace,log
>> >>  old-actions=kill_process,kill_thread,trap,errno,trace,log res=1
>> >>
>> >> If you then write the string "log log errno trace kill_process
>> >> kill_thread", which is unordered and contains the log action twice,
>> >>
>> >> it results in the same actions value as the previous record:
>> >>  type=CONFIG_CHANGE msg=audit(1525275325.613:142): op=seccomp-logging
>> >>  actions=kill_process,kill_thread,errno,trace,log
>> >>  old-actions=kill_process,kill_thread,errno,trace,log res=1
>> >>
>> >> No audit records are generated when reading the actions_logged sysctl.
>> >
>> > ACK for the format of the records.
>>
>> I just wanted to clarify the record format with you Steve ... the
>> "actions" and "old-actions" fields may not be included in the record
>> in cases where there is an error building the action value string, are
>> you okay with that or would you prefer the fields to always be
>> included but with a "?" for the value?
>
> A ? would be more in line with how other things are handled.

That's what I thought.

Would you mind putting together a v3 Tyler? :)

-- 
paul moore
www.paul-moore.com