[PATCH] tcp: allow restricting congestion control choices

[Stephen Hemminger <shemminger@osdl.org>]

Here is an alternative that allows runtime based restriction on some
TCP congestion control choices. 

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>

---
 include/net/tcp.h   |    1 +
 net/ipv4/tcp_cong.c |    4 ++++
 2 files changed, 5 insertions(+)

--- sky2.orig/include/net/tcp.h	2006-10-27 10:46:19.000000000 -0700
+++ sky2/include/net/tcp.h	2006-10-27 10:46:55.000000000 -0700
@@ -651,6 +651,7 @@
 
 	char 		name[TCP_CA_NAME_MAX];
 	struct module 	*owner;
+	int		restricted;	/* NET_ADMIN only */
 };
 
 extern int tcp_register_congestion_control(struct tcp_congestion_ops *type);
--- sky2.orig/net/ipv4/tcp_cong.c	2006-10-27 10:51:47.000000000 -0700
+++ sky2/net/ipv4/tcp_cong.c	2006-10-27 10:56:36.000000000 -0700
@@ -10,6 +10,7 @@
 #include <linux/mm.h>
 #include <linux/types.h>
 #include <linux/list.h>
+#include <linux/capability.h>
 #include <net/tcp.h>
 
 static DEFINE_SPINLOCK(tcp_cong_list_lock);
@@ -159,6 +160,9 @@
 	if (!ca)
 		err = -ENOENT;
 
+	else if (ca->restricted && !capable(CAP_NET_ADMIN))
+		err = -EPERM;
+
 	else if (!try_module_get(ca->owner))
 		err = -EBUSY;