From fcfa8e1efd4ccee4a497806c4eed5c71d2071b4c Mon Sep 17 00:00:00 2001
From: Gordon Tetlow <gordon@FreeBSD.org>
Date: Thu, 19 Mar 2020 16:50:36 +0000
Subject: [PATCH] Fix incorrect user-controlled pointer use in epair.

Approved by:	so
Security:	FreeBSD-SA-20:07.epair
Security:	CVE-2020-7452
---
 sys/net/if_clone.c | 19 +++++++++++++------
 sys/net/if_clone.h |  3 ++-
 sys/net/if_epair.c | 42 ++++++++++++++++++++----------------------
 3 files changed, 35 insertions(+), 29 deletions(-)

diff --git a/sys/net/if_clone.c b/sys/net/if_clone.c
index 6207ff0c037..acc392ead16 100644
--- a/sys/net/if_clone.c
+++ b/sys/net/if_clone.c
@@ -211,6 +211,18 @@ if_clone_create(char *name, size_t len, caddr_t params)
 	return (if_clone_createif(ifc, name, len, params));
 }
 
+void
+if_clone_addif(struct if_clone *ifc, struct ifnet *ifp)
+{
+
+	if ((ifc->ifc_flags & IFC_NOGROUP) == 0)
+		if_addgroup(ifp, ifc->ifc_name);
+
+	IF_CLONE_LOCK(ifc);
+	IFC_IFLIST_INSERT(ifc, ifp);
+	IF_CLONE_UNLOCK(ifc);
+}
+
 /*
  * Create a clone network interface.
  */
@@ -233,12 +245,7 @@ if_clone_createif(struct if_clone *ifc, char *name, size_t len, caddr_t params)
 		if (ifp == NULL)
 			panic("%s: lookup failed for %s", __func__, name);
 
-		if ((ifc->ifc_flags & IFC_NOGROUP) == 0)
-			if_addgroup(ifp, ifc->ifc_name);
-
-		IF_CLONE_LOCK(ifc);
-		IFC_IFLIST_INSERT(ifc, ifp);
-		IF_CLONE_UNLOCK(ifc);
+		if_clone_addif(ifc, ifp);
 	}
 
 	return (err);
diff --git a/sys/net/if_clone.h b/sys/net/if_clone.h
index 5dceacf68e0..b721e294119 100644
--- a/sys/net/if_clone.h
+++ b/sys/net/if_clone.h
@@ -79,7 +79,8 @@ int	if_clone_list(struct if_clonereq *);
 struct if_clone *if_clone_findifc(struct ifnet *);
 void	if_clone_addgroup(struct ifnet *, struct if_clone *);
 
-/* The below interface used only by epair(4). */
+/* The below interfaces are used only by epair(4). */
+void	if_clone_addif(struct if_clone *, struct ifnet *);
 int	if_clone_destroyif(struct if_clone *, struct ifnet *);
 
 #endif /* _KERNEL */
diff --git a/sys/net/if_epair.c b/sys/net/if_epair.c
index b28fe2b4bd3..376bdbe9117 100644
--- a/sys/net/if_epair.c
+++ b/sys/net/if_epair.c
@@ -711,6 +711,21 @@ epair_clone_match(struct if_clone *ifc, const char *name)
 	return (1);
 }
 
+static void
+epair_clone_add(struct if_clone *ifc, struct epair_softc *scb)
+{
+	struct ifnet *ifp;
+	uint8_t eaddr[ETHER_ADDR_LEN];	/* 00:00:00:00:00:00 */
+
+	ifp = scb->ifp;
+	/* Copy epairNa etheraddr and change the last byte. */
+	memcpy(eaddr, scb->oifp->if_hw_addr, ETHER_ADDR_LEN);
+	eaddr[5] = 0x0b;
+	ether_ifattach(ifp, eaddr);
+
+	if_clone_addif(ifc, ifp);
+}
+
 static int
 epair_clone_create(struct if_clone *ifc, char *name, size_t len, caddr_t params)
 {
@@ -723,24 +738,6 @@ epair_clone_create(struct if_clone *ifc, char *name, size_t len, caddr_t params)
 	uint32_t hash;
 	uint8_t eaddr[ETHER_ADDR_LEN];	/* 00:00:00:00:00:00 */
 
-	/*
-	 * We are abusing params to create our second interface.
-	 * Actually we already created it and called if_clone_create()
-	 * for it to do the official insertion procedure the moment we knew
-	 * it cannot fail anymore. So just do attach it here.
-	 */
-	if (params) {
-		scb = (struct epair_softc *)params;
-		ifp = scb->ifp;
-		/* Copy epairNa etheraddr and change the last byte. */
-		memcpy(eaddr, scb->oifp->if_hw_addr, ETHER_ADDR_LEN);
-		eaddr[5] = 0x0b;
-		ether_ifattach(ifp, eaddr);
-		/* Correctly set the name for the cloner list. */
-		strlcpy(name, ifp->if_xname, len);
-		return (0);
-	}
-
 	/* Try to see if a special unit was requested. */
 	error = ifc_name2unit(name, &unit);
 	if (error != 0)
@@ -891,10 +888,11 @@ epair_clone_create(struct if_clone *ifc, char *name, size_t len, caddr_t params)
 	if_setsendqready(ifp);
 	/* We need to play some tricks here for the second interface. */
 	strlcpy(name, epairname, len);
-	error = if_clone_create(name, len, (caddr_t)scb);
-	if (error)
-		panic("%s: if_clone_create() for our 2nd iface failed: %d",
-		    __func__, error);
+
+	/* Correctly set the name for the cloner list. */
+	strlcpy(name, scb->ifp->if_xname, len);
+	epair_clone_add(ifc, scb);
+
 	scb->if_qflush = ifp->if_qflush;
 	ifp->if_qflush = epair_qflush;
 	ifp->if_transmit = epair_transmit;
-- 
2.45.0