[bpf-next PATCH 2/3] bpf: sk_msg helpers for probe_* and *current_task*

[John Fastabend <john.fastabend@xxxxxxxxx>]

Often it is useful when applying policy to know something about the
task. If the administrator has CAP_SYS_ADMIN rights then they can
use kprobe + sk_msg and link the two programs together to accomplish
this. However, this is a bit clunky and also means we have to call
sk_msg program and kprobe program when we could just use a single
program and avoid passing metadata through sk_msg/skb, socket, etc.

To accomplish this add probe_* helpers to sk_msg programs guarded
by a CAP_SYS_ADMIN check. New supported helpers are the following,

 BPF_FUNC_get_current_task
 BPF_FUNC_current_task_under_cgroup
 BPF_FUNC_probe_read_user
 BPF_FUNC_probe_read_kernel
 BPF_FUNC_probe_read
 BPF_FUNC_probe_read_user_str
 BPF_FUNC_probe_read_kernel_str
 BPF_FUNC_probe_read_str

Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
---
 kernel/trace/bpf_trace.c |   16 ++++++++--------
 net/core/filter.c        |   34 ++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d961428..abe6721 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -147,7 +147,7 @@ BPF_CALL_3(bpf_probe_read_user, void *, dst, u32, size,
 	return ret;
 }
 
-static const struct bpf_func_proto bpf_probe_read_user_proto = {
+const struct bpf_func_proto bpf_probe_read_user_proto = {
 	.func		= bpf_probe_read_user,
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
@@ -167,7 +167,7 @@ BPF_CALL_3(bpf_probe_read_user_str, void *, dst, u32, size,
 	return ret;
 }
 
-static const struct bpf_func_proto bpf_probe_read_user_str_proto = {
+const struct bpf_func_proto bpf_probe_read_user_str_proto = {
 	.func		= bpf_probe_read_user_str,
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
@@ -198,7 +198,7 @@ BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size,
 	return bpf_probe_read_kernel_common(dst, size, unsafe_ptr, false);
 }
 
-static const struct bpf_func_proto bpf_probe_read_kernel_proto = {
+const struct bpf_func_proto bpf_probe_read_kernel_proto = {
 	.func		= bpf_probe_read_kernel,
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
@@ -213,7 +213,7 @@ BPF_CALL_3(bpf_probe_read_compat, void *, dst, u32, size,
 	return bpf_probe_read_kernel_common(dst, size, unsafe_ptr, true);
 }
 
-static const struct bpf_func_proto bpf_probe_read_compat_proto = {
+const struct bpf_func_proto bpf_probe_read_compat_proto = {
 	.func		= bpf_probe_read_compat,
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
@@ -253,7 +253,7 @@ BPF_CALL_3(bpf_probe_read_kernel_str, void *, dst, u32, size,
 	return bpf_probe_read_kernel_str_common(dst, size, unsafe_ptr, false);
 }
 
-static const struct bpf_func_proto bpf_probe_read_kernel_str_proto = {
+const struct bpf_func_proto bpf_probe_read_kernel_str_proto = {
 	.func		= bpf_probe_read_kernel_str,
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
@@ -268,7 +268,7 @@ BPF_CALL_3(bpf_probe_read_compat_str, void *, dst, u32, size,
 	return bpf_probe_read_kernel_str_common(dst, size, unsafe_ptr, true);
 }
 
-static const struct bpf_func_proto bpf_probe_read_compat_str_proto = {
+const struct bpf_func_proto bpf_probe_read_compat_str_proto = {
 	.func		= bpf_probe_read_compat_str,
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
@@ -874,7 +874,7 @@ BPF_CALL_0(bpf_get_current_task)
 	return (long) current;
 }
 
-static const struct bpf_func_proto bpf_get_current_task_proto = {
+const struct bpf_func_proto bpf_get_current_task_proto = {
 	.func		= bpf_get_current_task,
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
@@ -895,7 +895,7 @@ BPF_CALL_2(bpf_current_task_under_cgroup, struct bpf_map *, map, u32, idx)
 	return task_under_cgroup_hierarchy(current, cgrp);
 }
 
-static const struct bpf_func_proto bpf_current_task_under_cgroup_proto = {
+const struct bpf_func_proto bpf_current_task_under_cgroup_proto = {
 	.func           = bpf_current_task_under_cgroup,
 	.gpl_only       = false,
 	.ret_type       = RET_INTEGER,
diff --git a/net/core/filter.c b/net/core/filter.c
index 45b4a16..d1c4739 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6362,6 +6362,15 @@ sock_ops_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 const struct bpf_func_proto bpf_msg_redirect_map_proto __weak;
 const struct bpf_func_proto bpf_msg_redirect_hash_proto __weak;
 
+const struct bpf_func_proto bpf_current_task_under_cgroup_proto __weak;
+const struct bpf_func_proto bpf_get_current_task_proto __weak;
+const struct bpf_func_proto bpf_probe_read_user_proto __weak;
+const struct bpf_func_proto bpf_probe_read_user_str_proto __weak;
+const struct bpf_func_proto bpf_probe_read_kernel_proto __weak;
+const struct bpf_func_proto bpf_probe_read_kernel_str_proto __weak;
+const struct bpf_func_proto bpf_probe_read_compat_proto __weak;
+const struct bpf_func_proto bpf_probe_read_compat_str_proto __weak;
+
 static const struct bpf_func_proto *
 sk_msg_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -6397,6 +6406,31 @@ sk_msg_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_cgroup_classid_curr_proto;
 #endif
 	default:
+		break;
+	}
+
+	if (!capable(CAP_SYS_ADMIN))
+		return bpf_base_func_proto(func_id);
+
+	/* All helpers below are for CAP_SYS_ADMIN only */
+	switch (func_id) {
+	case BPF_FUNC_get_current_task:
+		return &bpf_get_current_task_proto;
+	case BPF_FUNC_current_task_under_cgroup:
+		return &bpf_current_task_under_cgroup_proto;
+	case BPF_FUNC_probe_read_user:
+		return &bpf_probe_read_user_proto;
+	case BPF_FUNC_probe_read_kernel:
+		return &bpf_probe_read_kernel_proto;
+	case BPF_FUNC_probe_read:
+		return &bpf_probe_read_compat_proto;
+	case BPF_FUNC_probe_read_user_str:
+		return &bpf_probe_read_user_str_proto;
+	case BPF_FUNC_probe_read_kernel_str:
+		return &bpf_probe_read_kernel_str_proto;
+	case BPF_FUNC_probe_read_str:
+		return &bpf_probe_read_compat_str_proto;
+	default:
 		return bpf_base_func_proto(func_id);
 	}
 }