Check user supplied interface name lengths

The original problem was that something like:

| strncpy(ifr.ifr_name, *argv, IFNAMSIZ);

might leave ifr.ifr_name unterminated if length of *argv exceeds
IFNAMSIZ. In order to fix this, I thought about replacing all those
cases with (equivalent) calls to snprintf() or even introducing
strlcpy(). But as Ulrich Drepper correctly pointed out when rejecting
the latter from being added to glibc, truncating a string without
notifying the user is not to be considered good practice. So let's
excercise what he suggested and reject empty, overlong or otherwise
invalid interface names right from the start - this way calls to
strncpy() like shown above become safe and the user has a chance to
reconsider what he was trying to do.

Note that this doesn't add calls to check_ifname() to all places where
user supplied interface name is parsed. In many cases, the interface
must exist already and is therefore looked up using ll_name_to_index(),
so if_nametoindex() will perform the necessary checks already.

Signed-off-by: Phil Sutter <phil@nwl.cc>

include/utils.h

@@ -133,6 +133,8 @@ void missarg(const char *) __attribute__((noreturn));
 void invarg(const char *, const char *) __attribute__((noreturn));
 void duparg(const char *, const char *) __attribute__((noreturn));
 void duparg2(const char *, const char *) __attribute__((noreturn));
+int check_ifname(const char *);
+int get_ifname(char *, const char *);
 int matches(const char *arg, const char *pattern);
 int inet_addr_match(const inet_prefix *a, const inet_prefix *b, int bits);
 

ip/ip6tunnel.c

@@ -273,7 +273,8 @@ static int parse_args(int argc, char **argv, int cmd, struct ip6_tnl_parm2 *p)
 				usage();
 			if (p->name[0])
 				duparg2("name", *argv);
-			strncpy(p->name, *argv, IFNAMSIZ - 1);
+			if (get_ifname(p->name, *argv))
+				invarg("\"name\" not a valid ifname", *argv);
 			if (cmd == SIOCCHGTUNNEL && count == 0) {
 				struct ip6_tnl_parm2 old_p = {};
 

ip/ipl2tp.c

@@ -182,7 +182,7 @@ static int create_session(struct l2tp_parm *p)
 	if (p->peer_cookie_len)
 		addattr_l(&req.n, 1024, L2TP_ATTR_PEER_COOKIE,
 			  p->peer_cookie,  p->peer_cookie_len);
-	if (p->ifname && p->ifname[0])
+	if (p->ifname)
 		addattrstrz(&req.n, 1024, L2TP_ATTR_IFNAME, p->ifname);
 
 	if (rtnl_talk(&genl_rth, &req.n, NULL, 0) < 0)
@@ -545,6 +545,8 @@ static int parse_args(int argc, char **argv, int cmd, struct l2tp_parm *p)
 			}
 		} else if (strcmp(*argv, "name") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"name\" not a valid ifname", *argv);
 			p->ifname = *argv;
 		} else if (strcmp(*argv, "remote") == 0) {
 			NEXT_ARG();

ip/iplink.c

@@ -573,6 +573,8 @@ int iplink_parse(int argc, char **argv, struct iplink_req *req,
 			req->i.ifi_flags &= ~IFF_UP;
 		} else if (strcmp(*argv, "name") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"name\" not a valid ifname", *argv);
 			*name = *argv;
 		} else if (strcmp(*argv, "index") == 0) {
 			NEXT_ARG();
@@ -848,6 +850,8 @@ int iplink_parse(int argc, char **argv, struct iplink_req *req,
 				NEXT_ARG();
 			if (*dev)
 				duparg2("dev", *argv);
+			if (check_ifname(*argv))
+				invarg("\"dev\" not a valid ifname", *argv);
 			*dev = *argv;
 			dev_index = ll_name_to_index(*dev);
 		}
@@ -870,7 +874,6 @@ int iplink_parse(int argc, char **argv, struct iplink_req *req,
 
 static int iplink_modify(int cmd, unsigned int flags, int argc, char **argv)
 {
-	int len;
 	char *dev = NULL;
 	char *name = NULL;
 	char *link = NULL;
@@ -960,13 +963,8 @@ static int iplink_modify(int cmd, unsigned int flags, int argc, char **argv)
 	}
 
 	if (name) {
-		len = strlen(name) + 1;
-		if (len == 1)
-			invarg("\"\" is not a valid device identifier\n",
-			       "name");
-		if (len > IFNAMSIZ)
-			invarg("\"name\" too long\n", name);
-		addattr_l(&req.n, sizeof(req), IFLA_IFNAME, name, len);
+		addattr_l(&req.n, sizeof(req),
+			  IFLA_IFNAME, name, strlen(name) + 1);
 	}
 
 	if (type) {
@@ -1016,7 +1014,6 @@ static int iplink_modify(int cmd, unsigned int flags, int argc, char **argv)
 
 int iplink_get(unsigned int flags, char *name, __u32 filt_mask)
 {
-	int len;
 	struct iplink_req req = {
 		.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg)),
 		.n.nlmsg_flags = NLM_F_REQUEST | flags,
@@ -1029,13 +1026,8 @@ int iplink_get(unsigned int flags, char *name, __u32 filt_mask)
 	} answer;
 
 	if (name) {
-		len = strlen(name) + 1;
-		if (len == 1)
-			invarg("\"\" is not a valid device identifier\n",
-				   "name");
-		if (len > IFNAMSIZ)
-			invarg("\"name\" too long\n", name);
-		addattr_l(&req.n, sizeof(req), IFLA_IFNAME, name, len);
+		addattr_l(&req.n, sizeof(req),
+			  IFLA_IFNAME, name, strlen(name) + 1);
 	}
 	addattr32(&req.n, sizeof(req), IFLA_EXT_MASK, filt_mask);
 
@@ -1265,6 +1257,8 @@ static int do_set(int argc, char **argv)
 			flags &= ~IFF_UP;
 		} else if (strcmp(*argv, "name") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"name\" not a valid ifname", *argv);
 			newname = *argv;
 		} else if (matches(*argv, "address") == 0) {
 			NEXT_ARG();
@@ -1355,6 +1349,8 @@ static int do_set(int argc, char **argv)
 
 			if (dev)
 				duparg2("dev", *argv);
+			if (check_ifname(*argv))
+				invarg("\"dev\" not a valid ifname", *argv);
 			dev = *argv;
 		}
 		argc--; argv++;
@@ -1383,9 +1379,6 @@ static int do_set(int argc, char **argv)
 	}
 
 	if (newname && strcmp(dev, newname)) {
-		if (strlen(newname) == 0)
-			invarg("\"\" is not a valid device identifier\n",
-			       "name");
 		if (do_changename(dev, newname) < 0)
 			return -1;
 		dev = newname;

ip/ipmaddr.c

@@ -284,7 +284,8 @@ static int multiaddr_modify(int cmd, int argc, char **argv)
 			NEXT_ARG();
 			if (ifr.ifr_name[0])
 				duparg("dev", *argv);
-			strncpy(ifr.ifr_name, *argv, IFNAMSIZ);
+			if (get_ifname(ifr.ifr_name, *argv))
+				invarg("\"dev\" not a valid ifname", *argv);
 		} else {
 			if (matches(*argv, "address") == 0) {
 				NEXT_ARG();

ip/iprule.c

@@ -472,11 +472,13 @@ static int iprule_list_flush_or_save(int argc, char **argv, int action)
 		} else if (strcmp(*argv, "dev") == 0 ||
 			   strcmp(*argv, "iif") == 0) {
 			NEXT_ARG();
-			strncpy(filter.iif, *argv, IFNAMSIZ);
+			if (get_ifname(filter.iif, *argv))
+				invarg("\"iif\"/\"dev\" not a valid ifname", *argv);
 			filter.iifmask = 1;
 		} else if (strcmp(*argv, "oif") == 0) {
 			NEXT_ARG();
-			strncpy(filter.oif, *argv, IFNAMSIZ);
+			if (get_ifname(filter.oif, *argv))
+				invarg("\"oif\" not a valid ifname", *argv);
 			filter.oifmask = 1;
 		} else if (strcmp(*argv, "l3mdev") == 0) {
 			filter.l3mdev = 1;
@@ -695,10 +697,14 @@ static int iprule_modify(int cmd, int argc, char **argv)
 		} else if (strcmp(*argv, "dev") == 0 ||
 			   strcmp(*argv, "iif") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"iif\"/\"dev\" not a valid ifname", *argv);
 			addattr_l(&req.n, sizeof(req), FRA_IFNAME,
 				  *argv, strlen(*argv)+1);
 		} else if (strcmp(*argv, "oif") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"oif\" not a valid ifname", *argv);
 			addattr_l(&req.n, sizeof(req), FRA_OIFNAME,
 				  *argv, strlen(*argv)+1);
 		} else if (strcmp(*argv, "l3mdev") == 0) {

ip/iptunnel.c

@@ -178,7 +178,8 @@ static int parse_args(int argc, char **argv, int cmd, struct ip_tunnel_parm *p)
 
 			if (p->name[0])
 				duparg2("name", *argv);
-			strncpy(p->name, *argv, IFNAMSIZ - 1);
+			if (get_ifname(p->name, *argv))
+				invarg("\"name\" not a valid ifname", *argv);
 			if (cmd == SIOCCHGTUNNEL && count == 0) {
 				struct ip_tunnel_parm old_p = {};
 
@@ -487,6 +488,8 @@ static int do_prl(int argc, char **argv)
 			count++;
 		} else if (strcmp(*argv, "dev") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"dev\" not a valid ifname", *argv);
 			medium = *argv;
 		} else {
 			fprintf(stderr,
@@ -534,6 +537,8 @@ static int do_6rd(int argc, char **argv)
 			cmd = SIOCDEL6RD;
 		} else if (strcmp(*argv, "dev") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"dev\" not a valid ifname", *argv);
 			medium = *argv;
 		} else {
 			fprintf(stderr,

ip/iptuntap.c

@@ -176,7 +176,8 @@ static int parse_args(int argc, char **argv,
 			ifr->ifr_flags |= IFF_MULTI_QUEUE;
 		} else if (matches(*argv, "dev") == 0) {
 			NEXT_ARG();
-			strncpy(ifr->ifr_name, *argv, IFNAMSIZ-1);
+			if (get_ifname(ifr->ifr_name, *argv))
+				invarg("\"dev\" not a valid ifname", *argv);
 		} else {
 			if (matches(*argv, "name") == 0) {
 				NEXT_ARG();
@@ -184,7 +185,8 @@ static int parse_args(int argc, char **argv,
 				usage();
 			if (ifr->ifr_name[0])
 				duparg2("name", *argv);
-			strncpy(ifr->ifr_name, *argv, IFNAMSIZ);
+			if (get_ifname(ifr->ifr_name, *argv))
+				invarg("\"name\" not a valid ifname", *argv);
 		}
 		count++;
 		argc--; argv++;

lib/utils.c

@@ -20,6 +20,7 @@
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <string.h>
+#include <ctype.h>
 #include <netdb.h>
 #include <arpa/inet.h>
 #include <asm/types.h>
@@ -699,6 +700,34 @@ void duparg2(const char *key, const char *arg)
 	exit(-1);
 }
 
+int check_ifname(const char *name)
+{
+	/* These checks mimic kernel checks in dev_valid_name */
+	if (*name == '\0')
+		return -1;
+	if (strlen(name) >= IFNAMSIZ)
+		return -1;
+
+	while (*name) {
+		if (*name == '/' || isspace(*name))
+			return -1;
+		++name;
+	}
+	return 0;
+}
+
+/* buf is assumed to be IFNAMSIZ */
+int get_ifname(char *buf, const char *name)
+{
+	int ret;
+
+	ret = check_ifname(name);
+	if (ret == 0)
+		strncpy(buf, name, IFNAMSIZ);
+
+	return ret;
+}
+
 int matches(const char *cmd, const char *pattern)
 {
 	int len = strlen(cmd);

misc/arpd.c

@@ -664,7 +664,8 @@ int main(int argc, char **argv)
 		struct ifreq ifr = {};
 
 		for (i = 0; i < ifnum; i++) {
-			strncpy(ifr.ifr_name, ifnames[i], IFNAMSIZ);
+			if (get_ifname(ifr.ifr_name, ifnames[i]))
+				invarg("not a valid ifname", ifnames[i]);
 			if (ioctl(udp_sock, SIOCGIFINDEX, &ifr)) {
 				perror("ioctl(SIOCGIFINDEX)");
 				exit(-1);

tc/f_flower.c

@@ -630,6 +630,8 @@ static int flower_parse_opt(struct filter_util *qu, char *handle,
 			flags |= TCA_CLS_FLAGS_SKIP_SW;
 		} else if (matches(*argv, "indev") == 0) {
 			NEXT_ARG();
+			if (check_ifname(*argv))
+				invarg("\"indev\" not a valid ifname", *argv);
 			addattrstrz(n, MAX_MSG, TCA_FLOWER_INDEV, *argv);
 		} else if (matches(*argv, "vlan_id") == 0) {
 			__u16 vid;