Introduce a sysctl that modifies the value of PROT_SOCK.

Add net.ipv4.ip_unprivileged_port_start, which is a per namespace sysctl
that denotes the first unprivileged inet port in the namespace.  To
disable all privileged ports set this to zero.  It also checks for
overlap with the local port range.  The privileged and local range may
not overlap.

The use case for this change is to allow containerized processes to bind
to priviliged ports, but prevent them from ever being allowed to modify
their container's network configuration.  The latter is accomplished by
ensuring that the network namespace is not a child of the user
namespace.  This modification was needed to allow the container manager
to disable a namespace's priviliged port restrictions without exposing
control of the network namespace to processes in the user namespace.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index aa1bb49f1dc6..17f2e7791042 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -822,6 +822,15 @@ ip_local_reserved_ports - list of comma separated ranges
 
 	Default: Empty
 
+ip_unprivileged_port_start - INTEGER
+	This is a per-namespace sysctl.  It defines the first
+	unprivileged port in the network namespace.  Privileged ports
+	require root or CAP_NET_BIND_SERVICE in order to bind to them.
+	To disable all privileged ports, set this to 0.  It may not
+	overlap with the ip_local_reserved_ports range.
+
+	Default: 1024
+
 ip_nonlocal_bind - BOOLEAN
 	If set, allows processes to bind() to non-local IP addresses,
 	which can be quite useful - but may break some applications.