linux-kernel - Re: [PATCH] seccomp: Only dump core when single-threaded

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Date:   Mon, 13 Feb 2017 22:37:26 -0800
From:   Andrei Vagin <avagin@...tuozzo.com>
To:     Kees Cook <keescook@...omium.org>
CC:     James Morris <james.l.morris@...cle.com>,
        Mike Frysinger <vapier@...too.org>,
        Paul Moore <paul@...l-moore.com>,
        Tyler Hicks <tyhicks@...onical.com>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] seccomp: Only dump core when single-threaded

On Tue, Feb 07, 2017 at 03:18:51PM -0800, Kees Cook wrote:
> The SECCOMP_RET_KILL filter return code has always killed the current
> thread, not the entire process. Changing this as a side-effect of dumping
> core isn't a safe thing to do (a few test suites have already flagged this
> behavioral change). Instead, restore the RET_KILL semantics, but still
> dump core when a RET_KILL delivers SIGSYS to a single-threaded process.
> 
> Fixes: b25e67161c29 ("seccomp: dump core when using SECCOMP_RET_KILL")
> Signed-off-by: Kees Cook <keescook@...omium.org>

All CRIU tests passed with this patch. Thanks!

Acked-by: Andrei Vagin <avagin@...tuozzo.com>

> ---
>  kernel/seccomp.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index f8f88ebcb3ba..e15185c28de5 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -643,11 +643,14 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>  	default: {
>  		siginfo_t info;
>  		audit_seccomp(this_syscall, SIGSYS, action);
> -		/* Show the original registers in the dump. */
> -		syscall_rollback(current, task_pt_regs(current));
> -		/* Trigger a manual coredump since do_exit skips it. */
> -		seccomp_init_siginfo(&info, this_syscall, data);
> -		do_coredump(&info);
> +		/* Dump core only if this is the last remaining thread. */
> +		if (get_nr_threads(current) == 1) {
> +			/* Show the original registers in the dump. */
> +			syscall_rollback(current, task_pt_regs(current));
> +			/* Trigger a manual coredump since do_exit skips it. */
> +			seccomp_init_siginfo(&info, this_syscall, data);
> +			do_coredump(&info);
> +		}
>  		do_exit(SIGSYS);
>  	}
>  	}
> -- 
> 2.7.4
> 
> 
> -- 
> Kees Cook
> Pixel Security