Re: [PATCH v3 2/2] ptrace, seccomp: add support for retrieving seccomp metadata

[Kees Cook <keescook@chromium.org>]

On Wed, Oct 11, 2017 at 8:39 AM, Tycho Andersen <tycho@docker.com> wrote:
> With the new SECCOMP_FILTER_FLAG_LOG, we need to be able to extract these
> flags for checkpoint restore, since they describe the state of a filter.
>
> So, let's add PTRACE_SECCOMP_GET_METADATA, similar to ..._GET_FILTER, which
> returns the metadata of the nth filter (right now, just the flags).
> Hopefully this will be future proof, and new per-filter metadata can be
> added to this struct.
>
> v3: * use GET_METADATA instead of GET_FLAGS
>
> Signed-off-by: Tycho Andersen <tycho@docker.com>
> CC: Kees Cook <keescook@chromium.org>
> CC: Andy Lutomirski <luto@amacapital.net>
> CC: Oleg Nesterov <oleg@redhat.com>

Applied for -next (with a minor whitespace fix).

Thanks!

-Kees

> ---
>  include/linux/seccomp.h     |  8 ++++++++
>  include/uapi/linux/ptrace.h |  6 ++++++
>  kernel/ptrace.c             |  4 ++++
>  kernel/seccomp.c            | 34 ++++++++++++++++++++++++++++++++++
>  4 files changed, 52 insertions(+)
>
> diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
> index c8bef436b61d..a6dee99cd187 100644
> --- a/include/linux/seccomp.h
> +++ b/include/linux/seccomp.h
> @@ -94,11 +94,19 @@ static inline void get_seccomp_filter(struct task_struct *tsk)
>  #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
>  extern long seccomp_get_filter(struct task_struct *task,
>                                unsigned long filter_off, void __user *data);
> +extern long seccomp_get_metadata(struct task_struct *task,
> +                                unsigned long filter_off, void __user *data);
>  #else
>  static inline long seccomp_get_filter(struct task_struct *task,
>                                       unsigned long n, void __user *data)
>  {
>         return -EINVAL;
>  }
> +static inline long seccomp_get_metadata(struct task_struct *task,
> +                                       unsigned long filter_off,
> +                                       void __user *data)
> +{
> +       return -EINVAL;
> +}
>  #endif /* CONFIG_SECCOMP_FILTER && CONFIG_CHECKPOINT_RESTORE */
>  #endif /* _LINUX_SECCOMP_H */
> diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
> index fb8106509000..4e9774812dba 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -65,6 +65,12 @@ struct ptrace_peeksiginfo_args {
>  #define PTRACE_SETSIGMASK      0x420b
>
>  #define PTRACE_SECCOMP_GET_FILTER      0x420c
> +#define PTRACE_SECCOMP_GET_METADATA    0x420d
> +
> +struct seccomp_metadata {
> +       unsigned long filter_off;       /* Input: which filter */
> +       unsigned int flags;             /* Output: filter's flags */
> +};
>
>  /* Read signals from a shared (process wide) queue */
>  #define PTRACE_PEEKSIGINFO_SHARED      (1 << 0)
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 84b1367935e4..58291e9f3276 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -1092,6 +1092,10 @@ int ptrace_request(struct task_struct *child, long request,
>                 ret = seccomp_get_filter(child, addr, datavp);
>                 break;
>
> +       case PTRACE_SECCOMP_GET_METADATA:
> +               ret = seccomp_get_metadata(child, addr, datavp);
> +               break;
> +
>         default:
>                 break;
>         }
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 2e1568261ac4..ea762af4974d 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1060,6 +1060,40 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
>         __put_seccomp_filter(filter);
>         return ret;
>  }
> +
> +long seccomp_get_metadata(struct task_struct *task,
> +                         unsigned long size, void __user *data)
> +{
> +       long ret;
> +       struct seccomp_filter *filter;
> +       struct seccomp_metadata kmd = {};
> +
> +       if (!capable(CAP_SYS_ADMIN) ||
> +           current->seccomp.mode != SECCOMP_MODE_DISABLED) {
> +               return -EACCES;
> +       }
> +
> +       size = min_t(unsigned long, size, sizeof(kmd));
> +
> +       if (copy_from_user(&kmd, data, size))
> +               return -EFAULT;
> +
> +       filter = get_nth_filter(task, kmd.filter_off);
> +       if (IS_ERR(filter))
> +               return PTR_ERR(filter);
> +
> +       memset(&kmd, 0, sizeof(kmd));
> +       if (filter->log)
> +               kmd.flags |= SECCOMP_FILTER_FLAG_LOG;
> +
> +       ret = size;
> +       if (copy_to_user(data, &kmd, size))
> +               ret = -EFAULT;
> +
> +       __put_seccomp_filter(filter);
> +       return ret;
> +
> +}
>  #endif
>
>  #ifdef CONFIG_SYSCTL
> --
> 2.11.0
>



-- 
Kees Cook
Pixel Security