Re: [PATCH v9 1/4] seccomp: hoist struct seccomp_data recalculation higher

["Serge E. Hallyn" <serge@hallyn.com>]

On Sun, Dec 02, 2018 at 08:28:24PM -0700, Tycho Andersen wrote:
> In the next patch, we're going to use the sd pointer passed to
> __seccomp_filter() as the data to pass to userspace. Except that in some
> cases (__seccomp_filter(SECCOMP_RET_TRACE), emulate_vsyscall(), every time
> seccomp is inovked on power, etc.) the sd pointer will be NULL in order to
> force seccomp to recompute the register data. Previously this recomputation
> happened one level lower, in seccomp_run_filters(); this patch just moves
> it up a level higher to __seccomp_filter().
> 
> Thanks Oleg for spotting this.
> 
> Signed-off-by: Tycho Andersen <tycho@tycho.ws>
> CC: Kees Cook <keescook@chromium.org>
> CC: Andy Lutomirski <luto@amacapital.net>
> CC: Oleg Nesterov <oleg@redhat.com>
> CC: Eric W. Biederman <ebiederm@xmission.com>
> CC: "Serge E. Hallyn" <serge@hallyn.com>

Acked-by: Serge Hallyn <serge@hallyn.com>

> CC: Christian Brauner <christian@brauner.io>
> CC: Tyler Hicks <tyhicks@canonical.com>
> CC: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
> ---
>  kernel/seccomp.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index f2ae2324c232..96afc32e041d 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -188,7 +188,6 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
>  static u32 seccomp_run_filters(const struct seccomp_data *sd,
>  			       struct seccomp_filter **match)
>  {
> -	struct seccomp_data sd_local;
>  	u32 ret = SECCOMP_RET_ALLOW;
>  	/* Make sure cross-thread synced filter points somewhere sane. */
>  	struct seccomp_filter *f =
> @@ -198,11 +197,6 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd,
>  	if (WARN_ON(f == NULL))
>  		return SECCOMP_RET_KILL_PROCESS;
>  
> -	if (!sd) {
> -		populate_seccomp_data(&sd_local);
> -		sd = &sd_local;
> -	}
> -
>  	/*
>  	 * All filters in the list are evaluated and the lowest BPF return
>  	 * value always takes priority (ignoring the DATA).
> @@ -658,6 +652,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>  	u32 filter_ret, action;
>  	struct seccomp_filter *match = NULL;
>  	int data;
> +	struct seccomp_data sd_local;
>  
>  	/*
>  	 * Make sure that any changes to mode from another thread have
> @@ -665,6 +660,11 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>  	 */
>  	rmb();
>  
> +	if (!sd) {
> +		populate_seccomp_data(&sd_local);
> +		sd = &sd_local;
> +	}
> +
>  	filter_ret = seccomp_run_filters(sd, &match);
>  	data = filter_ret & SECCOMP_RET_DATA;
>  	action = filter_ret & SECCOMP_RET_ACTION_FULL;
> -- 
> 2.19.1