Message-Id: <20171002114637.25703-4-phil@nwl.cc>
Date:   Mon,  2 Oct 2017 13:46:37 +0200
From:   Phil Sutter <phil@....cc>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org
Subject: [iproute PATCH v3 3/3] 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@....cc>
---
Changes since v2:
- Change implementation of check_ifname() and add get_ifname() just as
  Stephen suggested with one exception: Call strncpy() with length of
  IFNAMSIZ, otherwise it might leave destination unterminated.
- Change callers accordingly.

Changes since v1:
- Added missing check to tc/f_flower.c.
- Drop some useless checks from ip/ip{6,}tunnel.c (ll_name_to_index()
  will detect illegal interface names for us).
- Renamed assert_valid_dev_name() to the shorter check_ifname().
- iplink: Check 'name' and 'dev' parameters right where they are parsed.
- ipl2tp: Drop needless check for p->ifname[0].
---
 include/utils.h |  2 ++
 ip/ip6tunnel.c  |  3 ++-
 ip/ipl2tp.c     |  4 +++-
 ip/iplink.c     | 31 ++++++++++++-------------------
 ip/ipmaddr.c    |  3 ++-
 ip/iprule.c     | 10 ++++++++--
 ip/iptunnel.c   |  7 ++++++-
 ip/iptuntap.c   |  6 ++++--
 lib/utils.c     | 29 +++++++++++++++++++++++++++++
 misc/arpd.c     |  3 ++-
 tc/f_flower.c   |  2 ++
 11 files changed, 72 insertions(+), 28 deletions(-)

diff --git a/include/utils.h b/include/utils.h
index c9ed230b96044..76addb3258f59 100644
--- a/include/utils.h
+++ b/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);
 
diff --git a/ip/ip6tunnel.c b/ip/ip6tunnel.c
index c12d700e74189..bc44bef7f030c 100644
--- a/ip/ip6tunnel.c
+++ b/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 = {};
 
diff --git a/ip/ipl2tp.c b/ip/ipl2tp.c
index 88664c909e11f..1e37b175e3315 100644
--- a/ip/ipl2tp.c
+++ b/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();
diff --git a/ip/iplink.c b/ip/iplink.c
index ff5b56c038d28..6a96ea9ff56a7 100644
--- a/ip/iplink.c
+++ b/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;
diff --git a/ip/ipmaddr.c b/ip/ipmaddr.c
index 85a69e779563d..5683f6fa830c1 100644
--- a/ip/ipmaddr.c
+++ b/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();
diff --git a/ip/iprule.c b/ip/iprule.c
index 8313138db815f..36c57fa70b74a 100644
--- a/ip/iprule.c
+++ b/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) {
diff --git a/ip/iptunnel.c b/ip/iptunnel.c
index 0acfd0793d3cd..208a1f06ab12f 100644
--- a/ip/iptunnel.c
+++ b/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,
diff --git a/ip/iptuntap.c b/ip/iptuntap.c
index 451f7f0eac6bb..b46e452f21278 100644
--- a/ip/iptuntap.c
+++ b/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++;
diff --git a/lib/utils.c b/lib/utils.c
index bbd3cbc46a0e5..0cf99619c3021 100644
--- a/lib/utils.c
+++ b/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);
diff --git a/misc/arpd.c b/misc/arpd.c
index bfab44544ee1d..c2666f76fd5e9 100644
--- a/misc/arpd.c
+++ b/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);
diff --git a/tc/f_flower.c b/tc/f_flower.c
index 99e62a382dec6..b180210717394 100644
--- a/tc/f_flower.c
+++ b/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;
-- 
2.13.1

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