linux-kernel - Re: [PATCH v3 0/4] seccomp: Add SECCOMP_FILTER_FLAG_KILL

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Message-ID: <20170809202230.ivyv2cdeknb4tyn7@smitten>
Date:   Wed, 9 Aug 2017 14:22:30 -0600
From:   Tycho Andersen <tycho@...ker.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Tyler Hicks <tyhicks@...onical.com>,
        Fabricio Voznika <fvoznika@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Shuah Khan <shuah@...nel.org>,
        linux-kselftest@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v3 0/4] seccomp: Add SECCOMP_FILTER_FLAG_KILL_PROCESS

On Wed, Aug 09, 2017 at 12:01:53PM -0700, Kees Cook wrote:
> This series is the result of Fabricio and I going around a few times
> on possible solutions for finding a way to enhance RET_KILL to kill
> the process group. There's a lot of ways this could be done, but I
> wanted something that felt cleanest. As it happens, Tyler's recent
> patch series for logging improvement also needs to know a litte bit
> more during filter runs, and the solution for both is to pass back
> the matched filter. This lets us examine it here for RET_KILL and
> in the future for logging changes.
> 
> The filter passing is patch 1, the new flag for RET_KILL is patch 2.
> Some test refactoring is in patch 3 for the RET_DATA ordering, and
> patch 4 is the test for the new RET_KILL flag.
> 
> One thing missing is that CRIU will likely need to be updated, since
> saving/restoring seccomp filter _rules_ will not include the filter
> _flags_ for a process. This can be addressed separately.

Thanks for the heads up, I suppose PTRACE_SECCOMP_GET_FLAGS similar to
how PTRACE_SECCOMP_GET_FILTER works will be fine for this. One
question is: would we then also need to keep track of the TSYNC flag?
I don't think CRIU needs this to be correct, and we can grab the
KILL_PROCESS flag from filter->kill_process, so perhaps it's moot.

Anyway, happy to do this and the userspace part when this lands.

Cheers,

Tycho

> Please take a look!
> 
> Thanks,
> 
> -Kees
> 
> v3:
> - adjust seccomp_run_filters() to avoid later filters from masking
>   kill-process RET_KILL actions (drewry)
> - add test for masked RET_KILL.
> 
> v2:
> - moved kill_process bool into struct padding gap (tyhicks)
> - improved comments/docs in various places for clarify (tyhicks)
> - use ASSERT_TRUE() for WIFEXITED and WIFSIGNALLED (tyhicks)
> - adding Reviewed-bys from tyhicks
>