From: Lawrence Brakmo <brakmo@fb.com>
Date: Thu, 25 Jan 2018 16:14:05 -0800
Subject: bpf: Only reply field should be writeable
Patch-mainline: v4.16-rc1
Git-commit: 2585cd62f0986a6e6d9c83363ed6dbcc66bc9f32
References: bsc#1109837

Currently, a sock_ops BPF program can write the op field and all the
reply fields (reply and replylong). This is a bug. The op field should
not have been writeable and there is currently no way to use replylong
field for indices >= 1. This patch enforces that only the reply field
(which equals replylong[0]) is writeable.

Fixes: 40304b2a1567 ("bpf: BPF support for sock_ops")
Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/core/filter.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3700,8 +3700,7 @@ static bool sock_ops_is_valid_access(int
 {
 	if (type == BPF_WRITE) {
 		switch (off) {
-		case offsetof(struct bpf_sock_ops, op) ...
-		     offsetof(struct bpf_sock_ops, replylong[3]):
+		case offsetof(struct bpf_sock_ops, reply):
 			break;
 		default:
 			return false;