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 <ty...@tycho.ws>
> CC: Kees Cook <keesc...@chromium.org>
> CC: Andy Lutomirski <l...@amacapital.net>
> CC: Oleg Nesterov <o...@redhat.com>
> CC: Eric W. Biederman <ebied...@xmission.com>
> CC: "Serge E. Hallyn" <se...@hallyn.com>
Acked-by: Serge Hallyn <se...@hallyn.com>
> CC: Christian Brauner <christ...@brauner.io>
> CC: Tyler Hicks <tyhi...@canonical.com>
> CC: Akihiro Suda <suda.akih...@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
