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    Subject[PATCH AUTOSEL for 4.9 111/281] net: move somaxconn init from sysctl code
    Date
    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>
    ---
    net/core/net_namespace.c | 19 +++++++++++++++++++
    net/core/sysctl_net_core.c | 2 --
    2 files changed, 19 insertions(+), 2 deletions(-)

    diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
    index b7efe2f19f83..04fd04ccaa04 100644
    --- a/net/core/net_namespace.c
    +++ b/net/core/net_namespace.c
    @@ -312,6 +312,25 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
    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 ucounts *inc_net_namespaces(struct user_namespace *ns)
    diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
    index 1b4619008c4e..546ba76b35a5 100644
    --- a/net/core/sysctl_net_core.c
    +++ b/net/core/sysctl_net_core.c
    @@ -438,8 +438,6 @@ static __net_init int sysctl_core_net_init(struct net *net)
    {
    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);
    --
    2.14.1
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