netdev - [PATCH v5 bpf-next 1/3] bpf: add bpf_descendant

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Message-ID: <20190410203631.1576576-2-javierhonduco@fb.com>
Date:   Wed, 10 Apr 2019 13:36:29 -0700
From:   Javier Honduvilla Coto <javierhonduco@...com>
To:     <netdev@...r.kernel.org>
CC:     <yhs@...com>, <kernel-team@...com>
Subject: [PATCH v5 bpf-next 1/3] bpf: add bpf_descendant_of helper

This patch adds the bpf_descendant_of helper which accepts a PID and
returns 1 if the PID of the process currently being executed is a
descendant of it or if it's itself. Returns 0 otherwise.

This is very useful in tracing programs when we want to filter by a
given PID and all the children it might spawn. The current workarounds
most people implement for this purpose have issues:

- Attaching to process spawning syscalls and dynamically add those PIDs
  to some bpf map that would be used to filter is cumbersome and
potentially racy.
- Unrolling some loop to perform what this helper is doing consumes lots
  of instructions. That and the impossibility to jump backwards makes it
really hard to be correct in really large process chains.

Signed-off-by: Javier Honduvilla Coto <javierhonduco@...com>
---
 include/linux/bpf.h      |  1 +
 include/uapi/linux/bpf.h | 10 +++++++++-
 kernel/bpf/core.c        |  1 +
 kernel/bpf/helpers.c     | 27 +++++++++++++++++++++++++++
 kernel/trace/bpf_trace.c |  2 ++
 5 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 65f7094c40b4..0539999f07f3 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -967,6 +967,7 @@ 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_descendant_of_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 af1cbd951f26..f707b286c21d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2493,6 +2493,13 @@ union bpf_attr {
  * 	Return
  * 		0 if iph and th are a valid SYN cookie ACK, or a negative error
  * 		otherwise.
+ * int bpf_descendant_of(pid_t pid)
+ *	Description
+ *		This helper is useful in programs that want to filter events
+ *		happening to a pid or to any of its descendants.
+ *	Return
+ *		1 if the passed pid is an ancestor of the currently executing
+ *		process' pid or equal to it.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2595,7 +2602,8 @@ union bpf_attr {
 	FN(skb_ecn_set_ce),		\
 	FN(get_listener_sock),		\
 	FN(skc_lookup_tcp),		\
-	FN(tcp_check_syncookie),
+	FN(tcp_check_syncookie),	\
+	FN(descendant_of),
 
 /* 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 ace8c22c8b0e..df93d7157657 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2046,6 +2046,7 @@ 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_descendant_of_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 a411fc17d265..d04186c69042 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -18,6 +18,7 @@
 #include <linux/sched.h>
 #include <linux/uidgid.h>
 #include <linux/filter.h>
+#include <linux/init_task.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 +365,29 @@ const struct bpf_func_proto bpf_get_local_storage_proto = {
 };
 #endif
 #endif
+
+BPF_CALL_1(bpf_descendant_of, pid_t, pid)
+{
+	int result = 0;
+	struct task_struct *task = current;
+
+	if (pid == 0)
+		return 1;
+
+	while (task != &init_task) {
+		if (task->pid == pid) {
+			result = 1;
+			break;
+		}
+		task = rcu_dereference(task->real_parent);
+	}
+
+	return result;
+}
+
+const struct bpf_func_proto bpf_descendant_of_proto = {
+	.func		= bpf_descendant_of,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_ANYTHING,
+};
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d64c00afceb5..0968e38a2aae 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -599,6 +599,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_prandom_u32_proto;
 	case BPF_FUNC_probe_read_str:
 		return &bpf_probe_read_str_proto;
+	case BPF_FUNC_descendant_of:
+		return &bpf_descendant_of_proto;
 #ifdef CONFIG_CGROUPS
 	case BPF_FUNC_get_current_cgroup_id:
 		return &bpf_get_current_cgroup_id_proto;
-- 
2.17.1