Re: [PATCH bpf-next v11 2/4] bpf: added new helper bpf_get_ns_current_pid_tgid

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Sep 26, 2019 at 1:15 AM Carlos Neira <cneirabustos@gmail.com> wrote:
>
> New bpf helper bpf_get_ns_current_pid_tgid,
> This helper will return pid and tgid from current task
> which namespace matches dev_t and inode number provided,
> this will allows us to instrument a process inside a container.
>
> Signed-off-by: Carlos Neira <cneirabustos@gmail.com>
> ---
>  include/linux/bpf.h      |  1 +
>  include/uapi/linux/bpf.h | 18 +++++++++++++++++-
>  kernel/bpf/core.c        |  1 +
>  kernel/bpf/helpers.c     | 32 ++++++++++++++++++++++++++++++++
>  kernel/trace/bpf_trace.c |  2 ++
>  5 files changed, 53 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 5b9d22338606..231001475504 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1055,6 +1055,7 @@ extern const struct bpf_func_proto bpf_get_local_storage_proto;
>  extern const struct bpf_func_proto bpf_strtol_proto;
>  extern const struct bpf_func_proto bpf_strtoul_proto;
>  extern const struct bpf_func_proto bpf_tcp_sock_proto;
> +extern const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto;
>
>  /* Shared helpers among cBPF and eBPF. */
>  void bpf_user_rnd_init_once(void);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 77c6be96d676..9272dc8fb08c 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2750,6 +2750,21 @@ union bpf_attr {
>   *             **-EOPNOTSUPP** kernel configuration does not enable SYN cookies
>   *
>   *             **-EPROTONOSUPPORT** IP packet version is not 4 or 6
> + *
> + * int bpf_get_ns_current_pid_tgid(u32 dev, u64 inum)
> + *     Return
> + *             A 64-bit integer containing the current tgid and pid from current task

Function signature doesn't correspond to the actual return type (int vs u64).

> + *              which namespace inode and dev_t matches , and is create as such:
> + *             *current_task*\ **->tgid << 32 \|**
> + *             *current_task*\ **->pid**.
> + *
> + *             On failure, the returned value is one of the following:
> + *
> + *             **-EINVAL** if dev and inum supplied don't match dev_t and inode number
> + *              with nsfs of current task.
> + *
> + *             **-ENOENT** if /proc/self/ns does not exists.
> + *
>   */

[...]

>  #include "../../lib/kstrtox.h"
>
> @@ -487,3 +489,33 @@ const struct bpf_func_proto bpf_strtoul_proto = {
>         .arg4_type      = ARG_PTR_TO_LONG,
>  };
>  #endif
> +
> +BPF_CALL_2(bpf_get_ns_current_pid_tgid, u32, dev, u64, inum)

Just curious, is dev_t officially specified as u32 and is never
supposed to grow bigger? I wonder if accepting u64 might be more
future-proof API here?

> +{
> +       struct task_struct *task = current;
> +       struct pid_namespace *pidns;

[...]