The ancient and outdated concept of "privileged ports" in UNIX-type

OSes has probably caused more problems than it ever solved. Allow the
user to retire the old behavior by specifying their own privileged
range with,

  net.inet.ip.portrange.reservedhigh  default = IPPORT_RESERVED - 1
  net.inet.ip.portrange.reservedlo    default = 0

Now you can run that webserver without ever needing root at all. Or
just imagine, an ftpd that can really drop privileges, rather than
just set the euid, and still do PORT data transfers from 20/tcp.

Two edge cases to note,

  # sysctl net.inet.ip.portrange.reservedhigh=0

Opens all ports to everyone, and,

  # sysctl net.inet.ip.portrange.reservedhigh=65535

Locks all network activity to root only (which could actually have
been achieved before with ipfw(8), but is somewhat more
complicated).

For those who stick to the old religion that 0-1023 belong to root and
root alone, don't touch the knobs (or even lock them by raising
securelevel(8)), and nothing changes.

1 files changed, 15 insertions, 2 deletions

diff --git a/sys/netinet/in_pcb.c b/sys/netinet/in_pcb.c
index 46f824d..316977c 100644
--- a/sys/netinet/in_pcb.c
+++ b/sys/netinet/in_pcb.c
@@ -96,6 +96,14 @@ int	ipport_lastauto  = IPPORT_HILASTAUTO;		/* 65535 */
 int	ipport_hifirstauto = IPPORT_HIFIRSTAUTO;	/* 49152 */
 int	ipport_hilastauto  = IPPORT_HILASTAUTO;		/* 65535 */
 
+/*
+ * Reserved ports accessible only to root. There are significant
+ * security considerations that must be accounted for when changing these,
+ * but the security benefits can be great. Please be careful.
+ */
+int	ipport_reservedhigh = IPPORT_RESERVED - 1;	/* 1023 */
+int	ipport_reservedlow = 0;
+
 #define RANGECHK(var, min, max) \
 	if ((var) < (min)) { (var) = (min); } \
 	else if ((var) > (max)) { (var) = (max); }
@@ -132,6 +140,10 @@ SYSCTL_PROC(_net_inet_ip_portrange, OID_AUTO, hifirst, CTLTYPE_INT|CTLFLAG_RW,
 	   &ipport_hifirstauto, 0, &sysctl_net_ipport_check, "I", "");
 SYSCTL_PROC(_net_inet_ip_portrange, OID_AUTO, hilast, CTLTYPE_INT|CTLFLAG_RW,
 	   &ipport_hilastauto, 0, &sysctl_net_ipport_check, "I", "");
+SYSCTL_INT(_net_inet_ip_portrange, OID_AUTO, reservedhigh,
+	   CTLFLAG_RW|CTLFLAG_SECURE, &ipport_reservedhigh, 0, "");
+SYSCTL_INT(_net_inet_ip_portrange, OID_AUTO, reservedlow,
+	   CTLFLAG_RW|CTLFLAG_SECURE, &ipport_reservedlow, 0, "");
 
 /*
  * in_pcb.c: manage the Protocol Control Blocks.
@@ -288,8 +300,9 @@ in_pcbbind_setup(inp, nam, laddrp, lportp, td)
 		if (lport) {
 			struct inpcb *t;
 			/* GROSS */
-			if (ntohs(lport) < IPPORT_RESERVED && td &&
-			    suser_cred(td->td_ucred, PRISON_ROOT))
+			if (ntohs(lport) <= ipport_reservedhigh &&
+			    ntohs(lport) >= ipport_reservedlow &&
+			    td && suser_cred(td->td_ucred, PRISON_ROOT))
 				return (EACCES);
 			if (td && jailed(td->td_ucred))
 				prison = 1;