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Message-ID: <CAEf4BzZvTvGcyVfM=RB7GA+WHxsDkS+OGmUrNLpMhfa7bMBA1w@mail.gmail.com>
Date: Thu, 3 Oct 2019 10:30:06 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Carlos Antonio Neira Bustos <cneirabustos@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
Networking <netdev@...r.kernel.org>, Yonghong Song <yhs@...com>,
ebiederm@...ssion.com, Jesper Dangaard Brouer <brouer@...hat.com>,
bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH V12 2/4] bpf: added new helper bpf_get_ns_current_pid_tgid
On Thu, Oct 3, 2019 at 8:01 AM Carlos Antonio Neira Bustos
<cneirabustos@...il.com> wrote:
>
> On Wed, Oct 02, 2019 at 12:52:29PM +0200, Daniel Borkmann wrote:
> > On 10/1/19 11:41 PM, Carlos Neira 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@...il.com>
> > > ---
> > > include/linux/bpf.h | 1 +
> > > include/uapi/linux/bpf.h | 18 +++++++++++++++++-
> > > kernel/bpf/core.c | 1 +
> > > kernel/bpf/helpers.c | 36 ++++++++++++++++++++++++++++++++++++
> > > kernel/trace/bpf_trace.c | 2 ++
> > > 5 files changed, 57 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..ea8145d7f897 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
> > > + *
> > > + * u64 bpf_get_ns_current_pid_tgid(u64 dev, u64 inum)
> > > + * Return
> > > + * A 64-bit integer containing the current tgid and pid from current task
> > > + * 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, or if dev conversion to dev_t lost high bits.
> > > + *
> > > + * **-ENOENT** if /proc/self/ns does not exists.
> > > + *
> > > */
> > > #define __BPF_FUNC_MAPPER(FN) \
> > > FN(unspec), \
> > > @@ -2862,7 +2877,8 @@ union bpf_attr {
> > > FN(sk_storage_get), \
> > > FN(sk_storage_delete), \
> > > FN(send_signal), \
> > > - FN(tcp_gen_syncookie),
> > > + FN(tcp_gen_syncookie), \
> > > + FN(get_ns_current_pid_tgid),
> > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> > > * function eBPF program intends to call
> > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > > index 66088a9e9b9e..b2fd5358f472 100644
> > > --- a/kernel/bpf/core.c
> > > +++ b/kernel/bpf/core.c
> > > @@ -2042,6 +2042,7 @@ const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
> > > const struct bpf_func_proto bpf_get_current_comm_proto __weak;
> > > const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
> > > const struct bpf_func_proto bpf_get_local_storage_proto __weak;
> > > +const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto __weak;
> > > const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
> > > {
> > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > > index 5e28718928ca..8777181d1717 100644
> > > --- a/kernel/bpf/helpers.c
> > > +++ b/kernel/bpf/helpers.c
> > > @@ -11,6 +11,8 @@
> > > #include <linux/uidgid.h>
> > > #include <linux/filter.h>
> > > #include <linux/ctype.h>
> > > +#include <linux/pid_namespace.h>
> > > +#include <linux/proc_ns.h>
> > > #include "../../lib/kstrtox.h"
> > > @@ -487,3 +489,37 @@ const struct bpf_func_proto bpf_strtoul_proto = {
> > > .arg4_type = ARG_PTR_TO_LONG,
> > > };
> > > #endif
> > > +
> > > +BPF_CALL_2(bpf_get_ns_current_pid_tgid, u64, dev, u64, inum)
> > > +{
> > > + struct task_struct *task = current;
> > > + struct pid_namespace *pidns;
> > > + pid_t pid, tgid;
> > > +
> > > + if ((u64)(dev_t)dev != dev)
> > > + return -EINVAL;
> > > +
> > > + if (unlikely(!task))
> > > + return -EINVAL;
> > > +
> > > + pidns = task_active_pid_ns(task);
> > > + if (unlikely(!pidns))
> > > + return -ENOENT;
> > > +
> > > +
> > > + if (!ns_match(&pidns->ns, (dev_t)dev, inum))
> > > + return -EINVAL;
> > > +
> > > + pid = task_pid_nr_ns(task, pidns);
> > > + tgid = task_tgid_nr_ns(task, pidns);
> > > +
> > > + return (u64) tgid << 32 | pid;
> >
> > Basically here you are overlapping the 64-bit return value for the valid
> > outcome with the error codes above for the invalid case. If you look at
> > bpf_perf_event_read() we already had such broken occasion that bit us in
> > the past, and needed to introduce bpf_perf_event_read_value() instead.
> > Lets not go there again and design it similarly to the latter.
> >
> > > +}
> > > +
> > > +const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto = {
> > > + .func = bpf_get_ns_current_pid_tgid,
> > > + .gpl_only = false,
> > > + .ret_type = RET_INTEGER,
> > > + .arg1_type = ARG_ANYTHING,
> > > + .arg2_type = ARG_ANYTHING,
> > > +};
> > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > > index 44bd08f2443b..32331a1dcb6d 100644
> > > --- a/kernel/trace/bpf_trace.c
> > > +++ b/kernel/trace/bpf_trace.c
> > > @@ -735,6 +735,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> > > #endif
> > > case BPF_FUNC_send_signal:
> > > return &bpf_send_signal_proto;
> > > + case BPF_FUNC_get_ns_current_pid_tgid:
> > > + return &bpf_get_ns_current_pid_tgid_proto;
> > > default:
> > > return NULL;
> > > }
> > >
> >
> Daniel,
> If I understand correctly, to avoid problems I need to change the helper's function signature to something like the following:
>
> struct bpf_ns_current_pid_tgid_storage {
> __u64 dev;
> __u64 inum;
> __u64 pidtgid;
if you do it this way, please do
__u32 pid;
__u34 tgid;
I have to look up where pid and tgid is in that 64-bit number every
single time, let's not do it here for no good reason.
> };
>
> BPF_CALL_2(bpf_get_ns_current_pid_tgid,
> struct bpf_ns_current_pid_tgid_storage *, buf, u32, size);
>
> then use dev and inum provided by the user and return the requested
> value into pidtgid of the struct. Would that work?
>
> Thanks for your help.
>
>
>
>
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