[patch] sysctl to allow non-superusers to use ports <= 1023 without setpcaps

[William Pitcock]

Hello everyone,

This is a patch that adds a sysctl,  
net.ipv4.allow_lowport_nonsuperuser_bind, which removes the setpcaps/ 
sucaps/etc requirement for allowing a non-superuser process to use  
ports <= 1023.

The patch is below:

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index e4b1a4d..c3f7c3c 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -411,6 +411,7 @@ enum
	NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS=115,
	NET_TCP_DMA_COPYBREAK=116,
	NET_TCP_SLOW_START_AFTER_IDLE=117,
+	NET_IPV4_ALLOW_LOWPORT_BIND_NONSUPERUSER=118,
};
enum {
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index c84a320..a2ea829 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -394,6 +394,11 @@ int inet_release(struct socket *sock)
/* It is off by default, see below. */
int sysctl_ip_nonlocal_bind;
+/* When this is enabled, it allows normal users to bind to ports <=  
1023.
+ * This is set by the net.ipv4.allow_lowport_bind_nonsuperuser  
sysctl value.
+ */
+int sysctl_ip_allow_lowport_bind_nonsuperuser;
+
int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
{
	struct sockaddr_in *addr = (struct sockaddr_in *)uaddr;
@@ -432,7 +437,8 @@ int inet_bind(struct socket *sock, struc
	snum = ntohs(addr->sin_port);
	err = -EACCES;
-	if (snum && snum < PROT_SOCK && !capable(CAP_NET_BIND_SERVICE))
+	if (!sysctl_ip_allow_lowport_bind_nonsuperuser && snum && snum <  
PROT_SOCK &&
+		!capable(CAP_NET_BIND_SERVICE))
		goto out;
	/*      We keep a pair of addresses. rcv_saddr is the one
@@ -1412,3 +1418,4 @@ EXPORT_SYMBOL(inet_stream_ops);
EXPORT_SYMBOL(inet_unregister_protosw);
EXPORT_SYMBOL(net_statistics);
EXPORT_SYMBOL(sysctl_ip_nonlocal_bind);
+EXPORT_SYMBOL(sysctl_ip_allow_lowport_bind_nonsuperuser);
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 70cea9d..c57ef3a 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -20,6 +20,7 @@ #include <net/tcp.h>
/* From af_inet.c */
extern int sysctl_ip_nonlocal_bind;
+extern int sysctl_ip_allow_lowport_bind_nonsuperuser;
#ifdef CONFIG_SYSCTL
static int zero;
@@ -197,6 +198,14 @@ ctl_table ipv4_table[] = {
		.proc_handler	= &proc_dointvec
	},
	{
+		.ctl_name	= NET_IPV4_ALLOW_LOWPORT_BIND_NONSUPERUSER,
+		.procname	= "allow_lowport_bind_nonsuperuser",
+		.data		= &sysctl_ip_allow_lowport_bind_nonsuperuser,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec
+	},
+	{
		.ctl_name	= NET_IPV4_TCP_SYN_RETRIES,
		.procname	= "tcp_syn_retries",
		.data		= &sysctl_tcp_syn_retries,

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