Message-ID: <20190320164920.ha5ne7nlnu7fbx5i@dev00>
Date:   Wed, 20 Mar 2019 13:49:22 -0300
From:   Carlos Antonio Neira Bustos <cneirabustos@...il.com>
To:     netdev@...r.kernel.org
Cc:     ebiederm@...ssion.com, quentin.monnet@...ronome.com,
        ys114321@...il.com, brouer@...hat.com, cneirabustos@...il.com
Subject: [PATCH v3 bpf-next 1/3] BPF: helpers: New helper to obtain namespace
 data from current task


This is a series of patches to introduce a new helper called bpf_get_current_pidns_info,
this change has been splitted into the following patches:

1- Feature introduction
2- Update tools/.../bpf.h
3- Self tests and samples


>From 852a65906122b05b4d1a23af868b2c245d240402 Mon Sep 17 00:00:00 2001
From: Carlos <cneirabustos@...il.com>
Date: Tue, 19 Mar 2019 19:38:48 -0300
Subject: [PATCH] [PATCH bpf-next 1/3] BPF: New helper to obtain namespace data
 from current task

This helper obtains the active namespace from current and returns pid, tgid,
device and namespace id as seen from that namespace, allowing to instrument
a process inside a container.
Device is read from /proc/self/ns/pid, as in the future it's possible that
different pid_ns files may belong to different devices, according
to the discussion between Eric Biederman and Yonghong in 2017 linux plumbers
conference.
Currently bpf_get_current_pid_tgid(), is used to do pid filtering in bcc's
scripts but this helper returns the pid as seen by the root namespace which is
fine when a bcc script is not executed inside a container.
When the process of interest is inside a container, pid filtering will not work
if bpf_get_current_pid_tgid() is used. This helper addresses this limitation
returning the pid as it's seen by the current namespace where the script is
executing.

This helper has the same use cases as bpf_get_current_pid_tgid() as it can be
used to do pid filtering even inside a container.

For example a bcc script using bpf_get_current_pid_tgid() (tools/funccount.py):

        u32 pid = bpf_get_current_pid_tgid() >> 32;
        if (pid != <pid_arg_passed_in>)
                return 0;
Could be modified to use bpf_get_current_pidns_info() as follows:

        struct bpf_pidns pidns;
        bpf_get_current_pidns_info(&pidns, sizeof(struct bpf_pidns));
        u32 pid = pidns.tgid;
        u32 nsid = pidns.nsid;
        if ((pid != <pid_arg_passed_in>) && (nsid != <nsid_arg_passed_in>))
                return 0;

To find out the name PID namespace id of a process, you could use this command:

$ ps -h -o pidns -p <pid_of_interest>

Or this other command:

$ ls -Li /proc/<pid_of_interest>/ns/pid

Signed-off-by: Carlos Antonio Neira Bustos <cneirabustos@...il.com>
-
---
 include/linux/bpf.h      |  1 +
 include/uapi/linux/bpf.h | 26 ++++++++++++++++++-
 kernel/bpf/core.c        |  1 +
 kernel/bpf/helpers.c     | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/trace/bpf_trace.c |  2 ++
 5 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a2132e09dc1c..a77f5bd77bd8 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -930,6 +930,7 @@ extern const struct bpf_func_proto bpf_sk_redirect_map_proto;
 extern const struct bpf_func_proto bpf_spin_lock_proto;
 extern const struct bpf_func_proto bpf_spin_unlock_proto;
 extern const struct bpf_func_proto bpf_get_local_storage_proto;
+extern const struct bpf_func_proto bpf_get_current_pidns_info_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 3c38ac9a92a7..facc701c7873 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2366,6 +2366,18 @@ union bpf_attr {
  *             current value is ect (ECN capable). Works with IPv6 and IPv4.
  *     Return
  *             1 if set, 0 if not set.
+ *
+ * int bpf_get_current_pidns_info(struct bpf_pidns_info *pidns, u32 size_of_pidns)
+ *	Description
+ *		Copies into *pidns* pid, namespace id and tgid as seen by the
+ *		current namespace and also device from /proc/self/ns/pid.
+ *		*size_of_pidns* must be the size of *pidns*
+ *
+ *		This helper is used when pid filtering is needed inside a
+ *		container as bpf_get_current_tgid() helper returns always the
+ *		pid id as seen by the root namespace.
+ *	Return
+ *		0 on success -EINVAL on error.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2465,7 +2477,8 @@ union bpf_attr {
 	FN(spin_unlock),		\
 	FN(sk_fullsock),		\
 	FN(tcp_sock),			\
-	FN(skb_ecn_set_ce),
+	FN(skb_ecn_set_ce),		\
+	FN(get_current_pidns_info),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
@@ -3152,4 +3165,15 @@ struct bpf_line_info {
 struct bpf_spin_lock {
 	__u32	val;
 };
+
+/* helper bpf_get_current_pidns_info will store the following
+ * data, dev will contain major/minor from /proc/self/pid.
+*/
+struct bpf_pidns_info {
+	__u32 dev;
+	__u32 nsid;
+	__u32 tgid;
+	__u32 pid;
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 3f08c257858e..06329fbed95f 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2044,6 +2044,7 @@ 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_current_pidns_info __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 a411fc17d265..95c3780a6ba7 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -18,6 +18,11 @@
 #include <linux/sched.h>
 #include <linux/uidgid.h>
 #include <linux/filter.h>
+#include <linux/pid_namespace.h>
+#include <linux/major.h>
+#include <linux/stat.h>
+#include <linux/namei.h>
+#include <linux/version.h>
 
 /* If kernel subsystem is allowing eBPF programs to call this function,
  * inside its own verifier_ops->get_func_proto() callback it should return
@@ -364,3 +369,65 @@ const struct bpf_func_proto bpf_get_local_storage_proto = {
 };
 #endif
 #endif
+
+BPF_CALL_2(bpf_get_current_pidns_info, struct bpf_pidns_info *, pidns_info, u32,
+	 size)
+{
+	const char *nspid = "/proc/self/ns/pid";
+	struct pid_namespace *pidns = NULL;
+	struct kstat ks;
+	struct path kp;
+	pid_t tgid = 0;
+	pid_t pid = 0;
+	int res = 0;
+
+	if (unlikely(size != sizeof(struct bpf_pidns_info)))
+		goto clear;
+
+	pidns = task_active_pid_ns(current);
+
+	if (unlikely(!pidns))
+		goto clear;
+
+	pidns_info->nsid =  pidns->ns.inum;
+	pid = task_pid_nr_ns(current, pidns);
+
+	if (unlikely(!pid))
+		goto clear;
+
+	tgid = task_tgid_nr_ns(current, pidns);
+
+	if (unlikely(!tgid))
+		goto clear;
+
+	pidns_info->tgid = (u32) tgid;
+	pidns_info->pid = (u32) pid;
+
+        kern_path(nspid, 0, &kp);
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,11,0)
+    res = vfs_getattr(&kp, &ks, STATX_ALL, 0);
+#else
+    res = vfs_getattr(&kp, &ks);
+#endif
+       if (unlikely(res))
+               goto clear;
+
+       pidns_info->dev =  ks.dev;
+
+       return 0;
+
+       clear:
+	if (pidns_info)
+		memset((void *)pidns, 0, (size_t) size);
+
+	return -EINVAL;
+}
+
+const struct bpf_func_proto bpf_get_current_pidns_info_proto = {
+	.func	= bpf_get_current_pidns_info,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg2_type	= ARG_CONST_SIZE,
+};
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f1a86a0d881d..48c86bc8680f 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -604,6 +604,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_get_current_cgroup_id:
 		return &bpf_get_current_cgroup_id_proto;
 #endif
+	case BPF_FUNC_get_current_pidns_info:
+		return &bpf_get_current_pidns_info_proto;
 	default:
 		return NULL;
 	}
-- 
2.11.0

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