diff --git a/server/BandwidthController.cpp b/server/BandwidthController.cpp
index 4f9344c..e1db680 100644
--- a/server/BandwidthController.cpp
+++ b/server/BandwidthController.cpp
@@ -607,6 +607,8 @@
         ALOGE("Invalid bytes value. 1..max_int64.");
         return -1;
     }
+    if (!isIfaceName(iface))
+        return -1;
     if (StrncpyAndCheck(ifn, iface, sizeof(ifn))) {
         ALOGE("Interface name longer than %d", MAX_IFACENAME_LEN);
         return -1;
@@ -667,6 +669,8 @@
     std::list<std::string>::iterator it;
     const char *costName = "shared";
 
+    if (!isIfaceName(iface))
+        return -1;
     if (StrncpyAndCheck(ifn, iface, sizeof(ifn))) {
         ALOGE("Interface name longer than %d", MAX_IFACENAME_LEN);
         return -1;
@@ -706,10 +710,8 @@
     std::list<QuotaInfo>::iterator it;
     std::string quotaCmd;
 
-    if (!isNameLegal(iface)) {
-        ALOGE("setInterfaceQuota: Invalid iface \"%s\"", iface);
+    if (!isIfaceName(iface))
         return -1;
-    }
 
     if (!maxBytes) {
         /* Don't talk about -1, deprecate it. */
@@ -775,36 +777,13 @@
     return getInterfaceQuota("shared", bytes);
 }
 
-bool BandwidthController::isNameLegal(const char* name) {
-    size_t i;
-    size_t name_len = strlen(name);
-    if (name_len == 0) {
-        return false;
-    }
-
-    /* First character must be alphanumeric */
-    if (!isalnum(name[0])) {
-        return false;
-    }
-
-    for (i = 1; i < name_len; i++) {
-        if (!isalnum(name[i]) && (name[i] != '_') && (name[i] != '-') && (name[i] != ':')) {
-            return false;
-        }
-    }
-
-    return true;
-}
-
 int BandwidthController::getInterfaceQuota(const char *costName, int64_t *bytes) {
     FILE *fp;
     char *fname;
     int scanRes;
 
-    if (!isNameLegal(costName)) {
-        ALOGE("getInterfaceQuota: Invalid costName \"%s\"", costName);
+    if (!isIfaceName(costName))
         return -1;
-    }
 
     asprintf(&fname, "/proc/net/xt_quota/%s", costName);
     fp = fopen(fname, "r");
@@ -827,11 +806,8 @@
     const char *costName;
     std::list<QuotaInfo>::iterator it;
 
-    if (!isNameLegal(iface)) {
-        ALOGE("removeInterfaceQuota: Invalid iface \"%s\"", iface);
+    if (!isIfaceName(iface))
         return -1;
-    }
-
     if (StrncpyAndCheck(ifn, iface, sizeof(ifn))) {
         ALOGE("Interface name longer than %d", MAX_IFACENAME_LEN);
         return -1;
@@ -861,7 +837,7 @@
     FILE *fp;
     char *fname;
 
-    if (!isNameLegal(quotaName)) {
+    if (!isIfaceName(quotaName)) {
         ALOGE("updateQuota: Invalid quotaName \"%s\"", quotaName);
         return -1;
     }
@@ -1040,7 +1016,7 @@
 int BandwidthController::setInterfaceAlert(const char *iface, int64_t bytes) {
     std::list<QuotaInfo>::iterator it;
 
-    if (!isNameLegal(iface)) {
+    if (!isIfaceName(iface)) {
         ALOGE("setInterfaceAlert: Invalid iface \"%s\"", iface);
         return -1;
     }
@@ -1065,7 +1041,7 @@
 int BandwidthController::removeInterfaceAlert(const char *iface) {
     std::list<QuotaInfo>::iterator it;
 
-    if (!isNameLegal(iface)) {
+    if (!isIfaceName(iface)) {
         ALOGE("removeInterfaceAlert: Invalid iface \"%s\"", iface);
         return -1;
     }
@@ -1089,7 +1065,7 @@
     int res = 0;
     char *alertName;
 
-    if (!isNameLegal(costName)) {
+    if (!isIfaceName(costName)) {
         ALOGE("setCostlyAlert: Invalid costName \"%s\"", costName);
         return -1;
     }
@@ -1119,7 +1095,7 @@
     char *alertName;
     int res = 0;
 
-    if (!isNameLegal(costName)) {
+    if (!isIfaceName(costName)) {
         ALOGE("removeCostlyAlert: Invalid costName \"%s\"", costName);
         return -1;
     }
diff --git a/server/BandwidthController.h b/server/BandwidthController.h
index 6b7b5d3..2aca2cd 100644
--- a/server/BandwidthController.h
+++ b/server/BandwidthController.h
@@ -202,7 +202,6 @@
     std::list<int /*appUid*/> niceAppUids;
 
 private:
-    bool isNameLegal(const char* name);
     static const char *IPT_FLUSH_COMMANDS[];
     static const char *IPT_CLEANUP_COMMANDS[];
     static const char *IPT_SETUP_COMMANDS[];
diff --git a/server/ClatdController.cpp b/server/ClatdController.cpp
index b91b69a..4114de1 100644
--- a/server/ClatdController.cpp
+++ b/server/ClatdController.cpp
@@ -21,6 +21,7 @@
 #define LOG_TAG "ClatdController"
 #include <cutils/log.h>
 
+#include "NetdConstants.h"
 #include "ClatdController.h"
 #include "Fwmark.h"
 #include "NetdConstants.h"
@@ -42,6 +43,11 @@
         return -1;
     }
 
+    if (!isIfaceName(interface)) {
+        errno = ENOENT;
+        return -1;
+    }
+
     ALOGD("starting clatd");
 
     if ((pid = fork()) < 0) {
diff --git a/server/FirewallController.cpp b/server/FirewallController.cpp
index 0746316..17c6da4 100644
--- a/server/FirewallController.cpp
+++ b/server/FirewallController.cpp
@@ -69,6 +69,11 @@
 }
 
 int FirewallController::setInterfaceRule(const char* iface, FirewallRule rule) {
+    if (!isIfaceName(iface)) {
+        errno = ENOENT;
+        return -1;
+    }
+
     const char* op;
     if (rule == ALLOW) {
         op = "-I";
diff --git a/server/IdletimerController.cpp b/server/IdletimerController.cpp
index 76b79a7..ae7ae04 100644
--- a/server/IdletimerController.cpp
+++ b/server/IdletimerController.cpp
@@ -192,6 +192,11 @@
   int res;
   char timeout_str[11]; //enough to store any 32-bit unsigned decimal
 
+  if (!isIfaceName(iface)) {
+    errno = ENOENT;
+    return -1;
+  }
+
   snprintf(timeout_str, sizeof(timeout_str), "%u", timeout);
 
   const char *cmd1[] = {
diff --git a/server/InterfaceController.cpp b/server/InterfaceController.cpp
index e55114f..73e96ee 100644
--- a/server/InterfaceController.cpp
+++ b/server/InterfaceController.cpp
@@ -111,6 +111,7 @@
  */
 int InterfaceController::interfaceCommand(int argc, char *argv[], char **rbuf) {
 	int ret = -ENOSYS;
+	if (!isIfaceName(argv[2])) return -ENOENT;
 	if (sendCommand_)
 		ret = sendCommand_(argc, argv, rbuf);
 
@@ -119,6 +120,10 @@
 
 int InterfaceController::writeIPv6ProcPath(const char *interface, const char *setting, const char *value) {
 	char *path;
+	if (!isIfaceName(interface)) {
+		errno = ENOENT;
+		return -1;
+	}
 	asprintf(&path, "%s/%s/%s", ipv6_proc_path, interface, setting);
 	int success = writeFile(path, value, strlen(value));
 	free(path);
@@ -187,18 +192,25 @@
 	char buf[16];
 	int size = sizeof(buf);
 	char *path;
+	if (!isIfaceName(interface)) {
+		errno = ENOENT;
+		return -1;
+	}
 	asprintf(&path, "%s/%s/mtu", sys_net_path, interface);
 	int success = readFile(path, buf, &size);
 	if (!success && mtu)
 		*mtu = atoi(buf);
 	free(path);
 	return success;
-
 }
 
 int InterfaceController::setMtu(const char *interface, const char *mtu)
 {
 	char *path;
+	if (!isIfaceName(interface)) {
+		errno = ENOENT;
+		return -1;
+	}
 	asprintf(&path, "%s/%s/mtu", sys_net_path, interface);
 	int success = writeFile(path, mtu, strlen(mtu));
 	free(path);
diff --git a/server/NatController.cpp b/server/NatController.cpp
index 8391ad7..44b8b4a 100644
--- a/server/NatController.cpp
+++ b/server/NatController.cpp
@@ -134,11 +134,6 @@
     return 0;
 }
 
-bool NatController::checkInterface(const char *iface) {
-    if (strlen(iface) > IFNAMSIZ) return false;
-    return true;
-}
-
 int NatController::routesOp(bool add, const char *intIface, const char *extIface, char **argv, int addrCount) {
     unsigned netId = mNetCtrl->getNetworkId(extIface);
     int ret = 0;
@@ -171,8 +166,7 @@
 
     ALOGV("enableNat(intIface=<%s>, extIface=<%s>)",intIface, extIface);
 
-    if (!checkInterface(intIface) || !checkInterface(extIface)) {
-        ALOGE("Invalid interface specified");
+    if (!isIfaceName(intIface) || !isIfaceName(extIface)) {
         errno = ENODEV;
         return -1;
     }
@@ -409,8 +403,7 @@
     const char *intIface = argv[2];
     const char *extIface = argv[3];
 
-    if (!checkInterface(intIface) || !checkInterface(extIface)) {
-        ALOGE("Invalid interface specified");
+    if (!isIfaceName(intIface) || !isIfaceName(extIface)) {
         errno = ENODEV;
         return -1;
     }
diff --git a/server/NatController.h b/server/NatController.h
index 2912e4b..afddb27 100644
--- a/server/NatController.h
+++ b/server/NatController.h
@@ -50,7 +50,6 @@
 
     int setDefaults();
     int runCmd(int argc, const char **argv);
-    bool checkInterface(const char *iface);
     int setForwardRules(bool set, const char *intIface, const char *extIface);
     int setTetherCountingRules(bool add, const char *intIface, const char *extIface);
     int routesOp(bool add, const char *intIface, const char *extIface, char **argv, int addrCount);
diff --git a/server/NetdConstants.cpp b/server/NetdConstants.cpp
index c3c16eb..ea31410 100644
--- a/server/NetdConstants.cpp
+++ b/server/NetdConstants.cpp
@@ -17,6 +17,8 @@
 #include <fcntl.h>
 #include <string.h>
 #include <sys/wait.h>
+#include <ctype.h>
+#include <net/if.h>
 
 #define LOG_TAG "Netd"
 
@@ -143,3 +145,28 @@
     close(fd);
     return 0;
 }
+
+/*
+ * Check an interface name for plausibility. This should e.g. help against
+ * directory traversal.
+ */
+bool isIfaceName(const char *name) {
+    size_t i;
+    size_t name_len = strlen(name);
+    if ((name_len == 0) || (name_len > IFNAMSIZ)) {
+        return false;
+    }
+
+    /* First character must be alphanumeric */
+    if (!isalnum(name[0])) {
+        return false;
+    }
+
+    for (i = 1; i < name_len; i++) {
+        if (!isalnum(name[i]) && (name[i] != '_') && (name[i] != '-') && (name[i] != ':')) {
+            return false;
+        }
+    }
+
+    return true;
+}
diff --git a/server/NetdConstants.h b/server/NetdConstants.h
index e93347c..9b85d16 100644
--- a/server/NetdConstants.h
+++ b/server/NetdConstants.h
@@ -37,6 +37,7 @@
 int execIptablesSilently(IptablesTarget target, ...);
 int writeFile(const char *path, const char *value, int size);
 int readFile(const char *path, char *buf, int *sizep);
+bool isIfaceName(const char *name);
 
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof(*(a)))
 
diff --git a/server/SecondaryTableController.cpp b/server/SecondaryTableController.cpp
index 2ffb54d..398edd1 100644
--- a/server/SecondaryTableController.cpp
+++ b/server/SecondaryTableController.cpp
@@ -229,6 +229,11 @@
 }
 
 int SecondaryTableController::setFwmarkRule(const char *iface, bool add) {
+    if (!isIfaceName(iface)) {
+        errno = ENOENT;
+        return -1;
+    }
+
     unsigned netId = mNetCtrl->getNetworkId(iface);
 
     // Fail fast if any rules already exist for this interface
@@ -386,6 +391,11 @@
 
 int SecondaryTableController::setFwmarkRoute(const char* iface, const char *dest, int prefix,
                                              bool add) {
+    if (!isIfaceName(iface)) {
+        errno = ENOENT;
+        return -1;
+    }
+
     unsigned netId = mNetCtrl->getNetworkId(iface);
     char mark_str[11] = {0};
     char dest_str[44]; // enough to store an IPv6 address + 3 character bitmask
diff --git a/server/TetherController.cpp b/server/TetherController.cpp
index 93110e0..fbee5a2 100644
--- a/server/TetherController.cpp
+++ b/server/TetherController.cpp
@@ -31,6 +31,7 @@
 #include <cutils/log.h>
 #include <cutils/properties.h>
 
+#include "NetdConstants.h"
 #include "TetherController.h"
 
 TetherController::TetherController() {
@@ -273,6 +274,10 @@
 
 int TetherController::tetherInterface(const char *interface) {
     ALOGD("tetherInterface(%s)", interface);
+    if (!isIfaceName(interface)) {
+        errno = ENOENT;
+        return -1;
+    }
     mInterfaces->push_back(strdup(interface));
 
     if (applyDnsInterfaces()) {