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, 10 insertions, 0 deletions

diff --git a/include/net/ip.h b/include/net/ip.h
index ab6761a7c883..bf264a8db1ce 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -263,11 +263,21 @@ static inline bool sysctl_dev_name_is_allowed(const char *name)
 	return strcmp(name, "default") != 0  && strcmp(name, "all") != 0;
 }
 
+static inline int inet_prot_sock(struct net *net)
+{
+	return net->ipv4.sysctl_ip_prot_sock;
+}
+
 #else
 static inline int inet_is_local_reserved_port(struct net *net, int port)
 {
 	return 0;
 }
+
+static inline int inet_prot_sock(struct net *net)
+{
+	return PROT_SOCK;
+}
 #endif
 
 __be32 inet_current_timestamp(void);