netdev - [PATCH bpf] bpf: allow clearing all sock

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Message-ID: <20190415131042.1111-1-hoang.tran@uclouvain.be>
Date:   Mon, 15 Apr 2019 09:54:55 +0000
From:   Viet Hoang Tran <hoang.tran@...ouvain.be>
To:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Lawrence Brakmo <brakmo@...com>, Martin Lau <kafai@...com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        "tranviethoang.vn@...il.com" <tranviethoang.vn@...il.com>,
        Viet Hoang Tran <hoang.tran@...ouvain.be>
Subject: [PATCH bpf] bpf: allow clearing all sock_ops callback flags

The helper function bpf_sock_ops_cb_flags_set() can be used to both
set and clear the sock_ops callback flags. However, its current
behavior is not consistent. BPF program may clear a flag if more than
one were set, or replace a flag with another one, but cannot clear all
flags.

This patch also updates the documentation to clarify the ability to
clear flags of this helper function.

Signed-off-by: Hoang Tran <hoang.tran@...ouvain.be>
---
 include/uapi/linux/bpf.h | 9 ++++++++-
 net/core/filter.c        | 3 +--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 929c8e537a14..f9ee093fe8d3 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1694,12 +1694,19 @@ union bpf_attr {
  * 		error if an eBPF program tries to set a callback that is not
  * 		supported in the current kernel.
  *
- * 		The supported callback values that *argval* can combine are:
+ * 		*argval* is a flag array which can combine these flags:
  *
  * 		* **BPF_SOCK_OPS_RTO_CB_FLAG** (retransmission time out)
  * 		* **BPF_SOCK_OPS_RETRANS_CB_FLAG** (retransmission)
  * 		* **BPF_SOCK_OPS_STATE_CB_FLAG** (TCP state change)
  *
+ * 		Therefore, this function can be used to clear a callback flag by
+ * 		setting the appropriate bit to zero. e.g. to disable the RTO
+ * 		callback:
+ *
+ * 		**bpf_sock_ops_cb_flags_set(bpf_sock,**
+ * 			**bpf_sock->bpf_sock_ops_cb_flags & ~BPF_SOCK_OPS_RTO_CB_FLAG)**
+ *
  * 		Here are some examples of where one could call such eBPF
  * 		program:
  *
diff --git a/net/core/filter.c b/net/core/filter.c
index fc92ebc4e200..0c4cdfbb2fc7 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4355,8 +4355,7 @@ BPF_CALL_2(bpf_sock_ops_cb_flags_set, struct bpf_sock_ops_kern *, bpf_sock,
 	if (!IS_ENABLED(CONFIG_INET) || !sk_fullsock(sk))
 		return -EINVAL;
 
-	if (val)
-		tcp_sk(sk)->bpf_sock_ops_cb_flags = val;
+	tcp_sk(sk)->bpf_sock_ops_cb_flags = val;
 
 	return argval & (~BPF_SOCK_OPS_ALL_CB_FLAGS);
 }
-- 
2.17.1