4.4-stable review patch. If anyone has any objections, please let me know.
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From: Roman Kapl roman.kapl@sysgo.com
[ Upstream commit 7c3f1875c66fbc19762760097cabc91849ea0bbb ]
The default value for somaxconn is set in sysctl_core_net_init(), but this function is not called when kernel is configured without CONFIG_SYSCTL.
This results in the kernel not being able to accept TCP connections, because the backlog has zero size. Usually, the user ends up with: "TCP: request_sock_TCP: Possible SYN flooding on port 7. Dropping request. Check SNMP counters." If SYN cookies are not enabled the connection is rejected.
Before ef547f2ac16 (tcp: remove max_qlen_log), the effects were less severe, because the backlog was always at least eight slots long.
Signed-off-by: Roman Kapl roman.kapl@sysgo.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/net_namespace.c | 19 +++++++++++++++++++ net/core/sysctl_net_core.c | 2 -- 2 files changed, 19 insertions(+), 2 deletions(-)
--- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -310,6 +310,25 @@ out_undo: goto out; }
+static int __net_init net_defaults_init_net(struct net *net) +{ + net->core.sysctl_somaxconn = SOMAXCONN; + return 0; +} + +static struct pernet_operations net_defaults_ops = { + .init = net_defaults_init_net, +}; + +static __init int net_defaults_init(void) +{ + if (register_pernet_subsys(&net_defaults_ops)) + panic("Cannot initialize net default settings"); + + return 0; +} + +core_initcall(net_defaults_init);
#ifdef CONFIG_NET_NS static struct kmem_cache *net_cachep; --- a/net/core/sysctl_net_core.c +++ b/net/core/sysctl_net_core.c @@ -429,8 +429,6 @@ static __net_init int sysctl_core_net_in { struct ctl_table *tbl;
- net->core.sysctl_somaxconn = SOMAXCONN; - tbl = netns_core_table; if (!net_eq(net, &init_net)) { tbl = kmemdup(tbl, sizeof(netns_core_table), GFP_KERNEL);