Re: [PATCH v10 1/4] seccomp: hoist struct seccomp_data recalculation higher

[Kees Cook]

On Sun, Dec 9, 2018 at 10:24 AM Tycho Andersen <tycho@xxxxxxxx> 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@xxxxxxxx>

This is fine. :) Applied for -next.

-Kees

> CC: Kees Cook <keescook@xxxxxxxxxxxx>
> CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> CC: Oleg Nesterov <oleg@xxxxxxxxxx>
> CC: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> CC: "Serge E. Hallyn" <serge@xxxxxxxxxx>
> Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
> CC: Christian Brauner <christian@xxxxxxxxxx>
> CC: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
> CC: Akihiro Suda <suda.akihiro@xxxxxxxxxxxxx>
> ---
>  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
>


-- 
Kees Cook