Date:   Thu,  9 Aug 2018 09:18:00 -0400
From:   Carlos Neira <cneirabustos@...il.com>
To:     netdev@...r.kernel.org
Cc:     ebiederm@...ssion.com, quentin.monnet@...ronome.com,
        ys114321@...il.com, cneira <cneirabustos@...il.com>
Subject: [PATCH bpf-next] BPF: helpers: New helper to obtain namespace data from current task

From: cneira <cneirabustos@...il.com>

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_pid_tgid(&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                  | 24 +++++++++++-
 kernel/bpf/core.c                         |  1 +
 kernel/bpf/helpers.c                      | 64 +++++++++++++++++++++++++++++++
 kernel/trace/bpf_trace.c                  |  2 +
 samples/bpf/Makefile                      |  3 ++
 samples/bpf/trace_ns_info_user.c          | 35 +++++++++++++++++
 samples/bpf/trace_ns_info_user_kern.c     | 45 ++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h            | 25 +++++++++++-
 tools/testing/selftests/bpf/bpf_helpers.h |  3 ++
 10 files changed, 201 insertions(+), 2 deletions(-)
 create mode 100644 samples/bpf/trace_ns_info_user.c
 create mode 100644 samples/bpf/trace_ns_info_user_kern.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cd8790d2c6ed..3f4b999f7c99 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -787,6 +787,7 @@ extern const struct bpf_func_proto bpf_get_stack_proto;
 extern const struct bpf_func_proto bpf_sock_map_update_proto;
 extern const struct bpf_func_proto bpf_sock_hash_update_proto;
 extern const struct bpf_func_proto bpf_get_current_cgroup_id_proto;
+extern const struct bpf_func_proto bpf_get_current_pidns_info_proto;
 
 extern const struct bpf_func_proto bpf_get_local_storage_proto;
 
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index dd5758dc35d3..031e7d9dba09 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2113,6 +2113,18 @@ union bpf_attr {
  *		the shared data.
  *	Return
  *		Pointer to the local storage area.
+ *
+ * int bpf_get_current_pidns(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),			\
@@ -2196,7 +2208,8 @@ union bpf_attr {
 	FN(rc_keydown),			\
 	FN(skb_cgroup_id),		\
 	FN(get_current_cgroup_id),	\
-	FN(get_local_storage),
+	FN(get_local_storage),		\
+	FN(get_current_pidns_info),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
@@ -2724,4 +2737,13 @@ enum bpf_task_fd_type {
 	BPF_FD_TYPE_URETPROBE,		/* filename + offset */
 };
 
+/* 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 4d09e610777f..98ce53ce2ea6 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1796,6 +1796,7 @@ const struct bpf_func_proto bpf_sock_map_update_proto __weak;
 const struct bpf_func_proto bpf_sock_hash_update_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 1991466b8327..d06d723b9cff 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -18,6 +18,9 @@
 #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>
 
 /* If kernel subsystem is allowing eBPF programs to call this function,
  * inside its own verifier_ops->get_func_proto() callback it should return
@@ -214,3 +217,64 @@ const struct bpf_func_proto bpf_get_local_storage_proto = {
 	.arg2_type	= ARG_ANYTHING,
 };
 #endif
+
+BPF_CALL_2(bpf_get_current_pidns_info, struct bpf_pidns_info *, pidns_info, u32,
+	 size)
+{
+	const char *ppath = "/proc/self/ns/pid";
+	struct pid_namespace *pidns = NULL;
+	mm_segment_t oldsegfs;
+	struct kstat stat;
+	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;
+
+	oldsegfs = get_fs();
+	set_fs(KERNEL_DS);
+	res = vfs_stat((const char __user *)ppath, &stat);
+	set_fs(oldsegfs);
+
+	if (unlikely(res))
+		goto clear;
+
+	pidns_info->dev =  stat.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 0ae6829804bc..f70be29e49ab 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -568,6 +568,8 @@ 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;
 	}
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index f88d5683d6ee..fdcde00554ce 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -53,6 +53,7 @@ hostprogs-y += xdpsock
 hostprogs-y += xdp_fwd
 hostprogs-y += task_fd_query
 hostprogs-y += xdp_sample_pkts
+hostprogs-y += trace_ns_info
 
 # Libbpf dependencies
 LIBBPF = $(TOOLS_PATH)/lib/bpf/libbpf.a
@@ -109,6 +110,7 @@ xdpsock-objs := xdpsock_user.o
 xdp_fwd-objs := xdp_fwd_user.o
 task_fd_query-objs := bpf_load.o task_fd_query_user.o $(TRACE_HELPERS)
 xdp_sample_pkts-objs := xdp_sample_pkts_user.o $(TRACE_HELPERS)
+trace_ns_info-objs := bpf_load.o trace_ns_info_user.o
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
@@ -166,6 +168,7 @@ always += xdpsock_kern.o
 always += xdp_fwd_kern.o
 always += task_fd_query_kern.o
 always += xdp_sample_pkts_kern.o
+always += trace_ns_info_user_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
diff --git a/samples/bpf/trace_ns_info_user.c b/samples/bpf/trace_ns_info_user.c
new file mode 100644
index 000000000000..e06d08db6f30
--- /dev/null
+++ b/samples/bpf/trace_ns_info_user.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018 Carlos Neira cneirabustos@...il.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+
+#include <stdio.h>
+#include <linux/bpf.h>
+#include <unistd.h>
+#include "bpf/libbpf.h"
+#include "bpf_load.h"
+
+/* This code was taken verbatim from tracex1_user.c, it's used
+ * to exercize bpf_get_current_pidns_info() helper call.
+ */
+int main(int ac, char **argv)
+{
+	FILE *f;
+	char filename[256];
+
+	snprintf(filename, sizeof(filename), "%s_user_kern.o", argv[0]);
+	printf("loading %s\n", filename);
+
+	if (load_bpf_file(filename)) {
+		printf("%s", bpf_log_buf);
+		return 1;
+	}
+
+	f = popen("taskset 1 ping  localhost", "r");
+	(void) f;
+	read_trace_pipe();
+	return 0;
+}
diff --git a/samples/bpf/trace_ns_info_user_kern.c b/samples/bpf/trace_ns_info_user_kern.c
new file mode 100644
index 000000000000..ceaf3e83c8e7
--- /dev/null
+++ b/samples/bpf/trace_ns_info_user_kern.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018 Carlos Neira cneirabustos@...il.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/version.h>
+#include <uapi/linux/bpf.h>
+#include "bpf_helpers.h"
+
+typedef __u64 u64;
+typedef __u32 u32;
+
+
+/* kprobe is NOT a stable ABI
+ * kernel functions can be removed, renamed or completely change semantics.
+ * Number of arguments and their positions can change, etc.
+ * In such case this bpf+kprobe example will no longer be meaningful
+ */
+
+/* This will call bpf_get_current_pidns_info() to display pid and ns values
+ * as seen by the current namespace, on the far left you will see the pid as
+ * seen as by the root namespace.
+ */
+
+SEC("kprobe/__netif_receive_skb_core")
+int bpf_prog1(struct pt_regs *ctx)
+{
+	char fmt[] = "nsid:%u, dev: %u,  pid:%u\n";
+	struct bpf_pidns_info nsinfo;
+	int ok = 0;
+
+	ok = bpf_get_current_pidns_info(&nsinfo, sizeof(nsinfo));
+	if (ok == 0)
+		bpf_trace_printk(fmt, sizeof(fmt), (u32)nsinfo.nsid,
+				 (u32) nsinfo.dev, (u32)nsinfo.pid);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
+u32 _version SEC("version") = LINUX_VERSION_CODE;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index dd5758dc35d3..22fe6b0b6a74 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -173,6 +173,16 @@ enum bpf_attach_type {
 	__MAX_BPF_ATTACH_TYPE
 };
 
+/* 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;
+};
+
 #define MAX_BPF_ATTACH_TYPE __MAX_BPF_ATTACH_TYPE
 
 /* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
@@ -2113,6 +2123,18 @@ union bpf_attr {
  *		the shared data.
  *	Return
  *		Pointer to the local storage area.
+ *
+ * int bpf_get_current_pidns(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),			\
@@ -2196,7 +2218,8 @@ union bpf_attr {
 	FN(rc_keydown),			\
 	FN(skb_cgroup_id),		\
 	FN(get_current_cgroup_id),	\
-	FN(get_local_storage),
+	FN(get_local_storage),		\
+	FN(get_current_pidns_info),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index cb9fcfbc9307..c3060f3284e0 100644
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -137,6 +137,9 @@ static unsigned long long (*bpf_get_current_cgroup_id)(void) =
 	(void *) BPF_FUNC_get_current_cgroup_id;
 static void *(*bpf_get_local_storage)(void *map, unsigned long long flags) =
 	(void *) BPF_FUNC_get_local_storage;
+static int (*bpf_get_current_pidns_info)(struct bpf_pidns_info *buf,
+					 unsigned int buf_size) =
+	(void *) BPF_FUNC_get_current_pidns_info;
 
 /* llvm builtin functions that eBPF C program may use to
  * emit BPF_LD_ABS and BPF_LD_IND instructions
-- 
2.11.0

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