linux-kernel - [PATCH 2/5] tcp: small user

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Message-ID: <AANLkTi=H16k81X9yiAyxOO0Au2cK97o03hR008UUyxhL@mail.gmail.com>
Date:	Wed, 27 Oct 2010 17:28:07 +0400
From:	Dmitry Popov <dp@...hloadlab.com>
To:	"David S. Miller" <davem@...emloft.net>,
	William.Allen.Simpson@...il.com,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andreas Petlund <apetlund@...ula.no>,
	Shan Wei <shanwei@...fujitsu.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Octavian Purdila <opurdila@...acom.com>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Evgeniy Polyakov <zbr@...emap.net>,
	Laurent Chavey <chavey@...gle.com>,
	Gilad Ben-Yossef <gilad@...efidence.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"Steven J. Magnani" <steve@...idescorp.com>,
	Joe Perches <joe@...ches.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Yony Amit <yony@...sleep.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Artyom Gavrichenkov <ag@...hloadlab.com>
Subject: [PATCH 2/5] tcp: small user_mss code change

From: Dmitry Popov <dp@...hloadlab.com>

No double access to user_mss part of socket.

This is done to prevent possible race conditions if accessed without
socket lock.

Signed-off-by: Dmitry Popov <dp@...hloadlab.com>
---
 net/ipv4/tcp_ipv4.c   |    7 ++++---
 net/ipv4/tcp_output.c |    6 ++++--
 2 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 3de881e..c7e9b2a 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1510,6 +1510,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock
*sk, struct sk_buff *skb,
 	struct inet_sock *newinet;
 	struct tcp_sock *newtp;
 	struct sock *newsk;
+	int user_mss;
 #ifdef CONFIG_TCP_MD5SIG
 	struct tcp_md5sig_key *key;
 #endif
@@ -1545,9 +1546,9 @@ struct sock *tcp_v4_syn_recv_sock(struct sock
*sk, struct sk_buff *skb,
 	tcp_mtup_init(newsk);
 	tcp_sync_mss(newsk, dst_mtu(dst));
 	newtp->advmss = dst_metric(dst, RTAX_ADVMSS);
-	if (tcp_sk(sk)->rx_opt.user_mss &&
-	    tcp_sk(sk)->rx_opt.user_mss < newtp->advmss)
-		newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;
+	user_mss = tcp_sk(sk)->rx_opt.user_mss;
+	if (user_mss && user_mss < newtp->advmss)
+		newtp->advmss = user_mss;

 	tcp_initialize_rcv_mss(newsk);

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index eef2d66..561a7f3 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2416,6 +2416,7 @@ struct sk_buff *tcp_make_synack(struct sock *sk,
struct dst_entry *dst,
 	struct tcp_md5sig_key *md5;
 	int tcp_header_size;
 	int mss;
+	int user_mss;
 	int s_data_desired;

 	rcu_read_lock();
@@ -2439,8 +2440,9 @@ struct sk_buff *tcp_make_synack(struct sock *sk,
struct dst_entry *dst,
 	skb_dst_set(skb, dst_clone(dst));

 	mss = dst_metric(dst, RTAX_ADVMSS);
-	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
-		mss = tp->rx_opt.user_mss;
+	user_mss = tp->rx_opt.user_mss;
+	if (user_mss && user_mss < mss)
+		mss = user_mss;

 	if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
 		__u8 rcv_wscale;
--
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