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

From: Carlos Antonio Neira Bustos <[email-masked]>
Date: Fri, 27 Sep 2019 22:42:54 -0300

On Fri, Sep 27, 2019 at 10:24:46AM -0700, Andrii Nakryiko wrote:
> On Fri, Sep 27, 2019 at 9:59 AM Yonghong Song <[email-masked]> wrote:
> >
> >
> >
> > On 9/27/19 9:15 AM, Andrii Nakryiko wrote:
> > > On Thu, Sep 26, 2019 at 1:15 AM Carlos Neira <[email-masked]> 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 <[email-masked]>
> > >> ---
> > >>   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?
> >
> > This is what we have now in kernel (include/linux/types.h)
> > typedef u32 __kernel_dev_t;
> > typedef __kernel_dev_t          dev_t;
> >
> > But userspace dev_t (defined at /usr/include/sys/types.h) have
> > 8 bytes.
> >
> > Agree. Let us just use u64. It won't hurt and also will be fine
> > if kernel internal dev_t becomes 64bit.
> 
> Sounds good. Let's not forget to check that conversion to dev_t
> doesn't loose high bits, something like:
> 
> if ((u64)(dev_t)dev != dev)
>     return -E<something>;
> 
> >
> > >
> > >> +{
> > >> +       struct task_struct *task = current;
> > >> +       struct pid_namespace *pidns;
> > >
> > > [...]
> > >

Thanks Yonghong and Andrii,

I'll include these fixes on V12, I'll work on this over the weekend.

Bests