[PATCH] netns: correctly use per-netns ipv4 sysctl_tcp_mem

From: Yang Zhenzhang <redacted>

Now, kernel allows each net namespace to independently set up its levels
for tcp memory pressure thresholds.

But it seems there is a bug, as using the following steps:

[root@host socket]# lxc-start -n test -f config /bin/bash
[root@net-test socket]# ip route add default via 192.168.58.2
[root@net-test socket]# echo 0 0 0 > /proc/sys/net/ipv4/tcp_mem
[root@net-test socket]# scp root@192.168.58.174:/home/tcp_mem_test .

and it still can transport the "tcp_mem_test" file which we hope it
would not.

It's because inet_init() (net/ipv4/af_inet.c)initialize the
tcp_prot.sysctl_mem:
tcp_prot.sysctl_mem = init_net.ipv4.sysctl_tcp_mem;

So when the protocal is TCP, sk->sk_prot->sysctl_mem(following code)
always use the ipv4 sysctl_tcp_mem of init_net namespace rather than
it's own net namespace.
This patch simply set "prot" equal to net->ipv4.sysctl_tcp_mem when
the protocol type is TCP.

Signed-off-by: Yang Zhenzhang <redacted>
---
 include/net/sock.h |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 4a45216..b62a8d9 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h

@@ -59,6 +59,7 @@
 #include <linux/static_key.h>
 #include <linux/aio.h>
 #include <linux/sched.h>
+#include <linux/in.h>

 #include <linux/filter.h>
 #include <linux/rculist_nulls.h>

@@ -1062,7 +1063,12 @@ static inline void sk_enter_memory_pressure(struct sock *sk)

 static inline long sk_prot_mem_limits(const struct sock *sk, int index)
 {
+	struct net *net = sock_net(sk);
 	long *prot = sk->sk_prot->sysctl_mem;
+	
+	if (sk->protocol == IPPROTO_TCP)
+		prot = net->ipv4.sysctl_tcp_mem;
+
 	if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
 		prot = sk->sk_cgrp->sysctl_mem;
 	return prot[index];

-- 
1.7.1