[iproute PATCH v2] ip-route: Fix segfault with many nexthops

[Phil Sutter <phil@nwl.cc>]

It was possible to crash ip-route by adding an IPv6 route with 37
nexthop statements. A simple reproducer is:

| for i in `seq 37`; do
| 	nhs="nexthop via 1111::$i "$nhs
| done
| ip -6 route add 3333::/64 $nhs

The related code was broken in multiple ways:

* parse_one_nh() assumed that rta points to 4kB of storage but caller
  provided just 1kB. Fixed by passing 'len' parameter with the correct
  value.

* Error checking of rta_addattr*() calls in parse_one_nh() and called
  functions was completely absent, so with above fix in place output
  flood would occur due to parser looping forever.

While being at it, increase message buffer sizes to 4k. This allows for
at most 144 nexthops.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
Changes since v1:
- Remove accidentally added 'return 0' line from parse_nexthops().
- Increase buffer sizes.
---
 ip/iproute.c          |  43 ++++++++++-------
 ip/iproute_lwtunnel.c | 108 +++++++++++++++++++++++++-----------------
 2 files changed, 91 insertions(+), 60 deletions(-)

diff --git a/ip/iproute.c b/ip/iproute.c
index 30833414a3f7f..398322fd1f4ff 100644
--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -941,7 +941,7 @@ int print_route(const struct sockaddr_nl *who, struct nlmsghdr *n, void *arg)
 }
 
 static int parse_one_nh(struct nlmsghdr *n, struct rtmsg *r,
-			struct rtattr *rta, struct rtnexthop *rtnh,
+			struct rtattr *rta, size_t len, struct rtnexthop *rtnh,
 			int *argcp, char ***argvp)
 {
 	int argc = *argcp;
@@ -962,11 +962,16 @@ static int parse_one_nh(struct nlmsghdr *n, struct rtmsg *r,
 			if (r->rtm_family == AF_UNSPEC)
 				r->rtm_family = addr.family;
 			if (addr.family == r->rtm_family) {
-				rta_addattr_l(rta, 4096, RTA_GATEWAY, &addr.data, addr.bytelen);
-				rtnh->rtnh_len += sizeof(struct rtattr) + addr.bytelen;
+				if (rta_addattr_l(rta, len, RTA_GATEWAY,
+						  &addr.data, addr.bytelen))
+					return -1;
+				rtnh->rtnh_len += sizeof(struct rtattr)
+						  + addr.bytelen;
 			} else {
-				rta_addattr_l(rta, 4096, RTA_VIA, &addr.family, addr.bytelen+2);
-				rtnh->rtnh_len += RTA_SPACE(addr.bytelen+2);
+				if (rta_addattr_l(rta, len, RTA_VIA,
+						  &addr.family, addr.bytelen + 2))
+					return -1;
+				rtnh->rtnh_len += RTA_SPACE(addr.bytelen + 2);
 			}
 		} else if (strcmp(*argv, "dev") == 0) {
 			NEXT_ARG();
@@ -988,13 +993,15 @@ static int parse_one_nh(struct nlmsghdr *n, struct rtmsg *r,
 			NEXT_ARG();
 			if (get_rt_realms_or_raw(&realm, *argv))
 				invarg("\"realm\" value is invalid\n", *argv);
-			rta_addattr32(rta, 4096, RTA_FLOW, realm);
+			if (rta_addattr32(rta, len, RTA_FLOW, realm))
+				return -1;
 			rtnh->rtnh_len += sizeof(struct rtattr) + 4;
 		} else if (strcmp(*argv, "encap") == 0) {
-			int len = rta->rta_len;
+			int old_len = rta->rta_len;
 
-			lwt_parse_encap(rta, 4096, &argc, &argv);
-			rtnh->rtnh_len += rta->rta_len - len;
+			if (lwt_parse_encap(rta, len, &argc, &argv))
+				return -1;
+			rtnh->rtnh_len += rta->rta_len - old_len;
 		} else if (strcmp(*argv, "as") == 0) {
 			inet_prefix addr;
 
@@ -1002,8 +1009,9 @@ static int parse_one_nh(struct nlmsghdr *n, struct rtmsg *r,
 			if (strcmp(*argv, "to") == 0)
 				NEXT_ARG();
 			get_addr(&addr, *argv, r->rtm_family);
-			rta_addattr_l(rta, 4096, RTA_NEWDST, &addr.data,
-				      addr.bytelen);
+			if (rta_addattr_l(rta, len, RTA_NEWDST,
+					  &addr.data, addr.bytelen))
+				return -1;
 			rtnh->rtnh_len += sizeof(struct rtattr) + addr.bytelen;
 		} else
 			break;
@@ -1016,7 +1024,7 @@ static int parse_one_nh(struct nlmsghdr *n, struct rtmsg *r,
 static int parse_nexthops(struct nlmsghdr *n, struct rtmsg *r,
 			  int argc, char **argv)
 {
-	char buf[1024];
+	char buf[4096];
 	struct rtattr *rta = (void *)buf;
 	struct rtnexthop *rtnh;
 
@@ -1036,7 +1044,7 @@ static int parse_nexthops(struct nlmsghdr *n, struct rtmsg *r,
 		memset(rtnh, 0, sizeof(*rtnh));
 		rtnh->rtnh_len = sizeof(*rtnh);
 		rta->rta_len += rtnh->rtnh_len;
-		if (parse_one_nh(n, r, rta, rtnh, &argc, &argv)) {
+		if (parse_one_nh(n, r, rta, 4096, rtnh, &argc, &argv)) {
 			fprintf(stderr, "Error: cannot parse nexthop\n");
 			exit(-1);
 		}
@@ -1044,7 +1052,8 @@ static int parse_nexthops(struct nlmsghdr *n, struct rtmsg *r,
 	}
 
 	if (rta->rta_len > RTA_LENGTH(0))
-		addattr_l(n, 1024, RTA_MULTIPATH, RTA_DATA(rta), RTA_PAYLOAD(rta));
+		return addattr_l(n, 4096, RTA_MULTIPATH,
+				 RTA_DATA(rta), RTA_PAYLOAD(rta));
 	return 0;
 }
 
@@ -1053,7 +1062,7 @@ static int iproute_modify(int cmd, unsigned int flags, int argc, char **argv)
 	struct {
 		struct nlmsghdr	n;
 		struct rtmsg		r;
-		char			buf[1024];
+		char			buf[4096];
 	} req = {
 		.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)),
 		.n.nlmsg_flags = NLM_F_REQUEST | flags,
@@ -1484,8 +1493,8 @@ static int iproute_modify(int cmd, unsigned int flags, int argc, char **argv)
 		addattr_l(&req.n, sizeof(req), RTA_METRICS, RTA_DATA(mxrta), RTA_PAYLOAD(mxrta));
 	}
 
-	if (nhs_ok)
-		parse_nexthops(&req.n, &req.r, argc, argv);
+	if (nhs_ok && parse_nexthops(&req.n, &req.r, argc, argv))
+		return -1;
 
 	if (req.r.rtm_family == AF_UNSPEC)
 		req.r.rtm_family = AF_INET;
diff --git a/ip/iproute_lwtunnel.c b/ip/iproute_lwtunnel.c
index e604481142ec1..969a4763df71d 100644
--- a/ip/iproute_lwtunnel.c
+++ b/ip/iproute_lwtunnel.c
@@ -538,8 +538,9 @@ static int parse_encap_seg6(struct rtattr *rta, size_t len, int *argcp,
 
 	memcpy(tuninfo->srh, srh, srhlen);
 
-	rta_addattr_l(rta, len, SEG6_IPTUNNEL_SRH, tuninfo,
-		      sizeof(*tuninfo) + srhlen);
+	if (rta_addattr_l(rta, len, SEG6_IPTUNNEL_SRH, tuninfo,
+			  sizeof(*tuninfo) + srhlen))
+		return -1;
 
 	free(tuninfo);
 	free(srh);
@@ -611,6 +612,7 @@ static int parse_encap_seg6local(struct rtattr *rta, size_t len, int *argcp,
 	char segbuf[1024];
 	inet_prefix addr;
 	__u32 hmac = 0;
+	int ret = 0;
 
 	while (argc > 0) {
 		if (strcmp(*argv, "action") == 0) {
@@ -620,27 +622,28 @@ static int parse_encap_seg6local(struct rtattr *rta, size_t len, int *argcp,
 			action = read_action_type(*argv);
 			if (!action)
 				invarg("\"action\" value is invalid\n", *argv);
-			rta_addattr32(rta, len, SEG6_LOCAL_ACTION, action);
+			ret = rta_addattr32(rta, len, SEG6_LOCAL_ACTION,
+					    action);
 		} else if (strcmp(*argv, "table") == 0) {
 			NEXT_ARG();
 			if (table_ok++)
 				duparg2("table", *argv);
 			get_u32(&table, *argv, 0);
-			rta_addattr32(rta, len, SEG6_LOCAL_TABLE, table);
+			ret = rta_addattr32(rta, len, SEG6_LOCAL_TABLE, table);
 		} else if (strcmp(*argv, "nh4") == 0) {
 			NEXT_ARG();
 			if (nh4_ok++)
 				duparg2("nh4", *argv);
 			get_addr(&addr, *argv, AF_INET);
-			rta_addattr_l(rta, len, SEG6_LOCAL_NH4, &addr.data,
-				      addr.bytelen);
+			ret = rta_addattr_l(rta, len, SEG6_LOCAL_NH4,
+					    &addr.data, addr.bytelen);
 		} else if (strcmp(*argv, "nh6") == 0) {
 			NEXT_ARG();
 			if (nh6_ok++)
 				duparg2("nh6", *argv);
 			get_addr(&addr, *argv, AF_INET6);
-			rta_addattr_l(rta, len, SEG6_LOCAL_NH6, &addr.data,
-				      addr.bytelen);
+			ret = rta_addattr_l(rta, len, SEG6_LOCAL_NH6,
+					    &addr.data, addr.bytelen);
 		} else if (strcmp(*argv, "iif") == 0) {
 			NEXT_ARG();
 			if (iif_ok++)
@@ -648,7 +651,7 @@ static int parse_encap_seg6local(struct rtattr *rta, size_t len, int *argcp,
 			iif = ll_name_to_index(*argv);
 			if (!iif)
 				exit(nodev(*argv));
-			rta_addattr32(rta, len, SEG6_LOCAL_IIF, iif);
+			ret = rta_addattr32(rta, len, SEG6_LOCAL_IIF, iif);
 		} else if (strcmp(*argv, "oif") == 0) {
 			NEXT_ARG();
 			if (oif_ok++)
@@ -656,7 +659,7 @@ static int parse_encap_seg6local(struct rtattr *rta, size_t len, int *argcp,
 			oif = ll_name_to_index(*argv);
 			if (!oif)
 				exit(nodev(*argv));
-			rta_addattr32(rta, len, SEG6_LOCAL_OIF, oif);
+			ret = rta_addattr32(rta, len, SEG6_LOCAL_OIF, oif);
 		} else if (strcmp(*argv, "srh") == 0) {
 			NEXT_ARG();
 			if (srh_ok++)
@@ -691,6 +694,8 @@ static int parse_encap_seg6local(struct rtattr *rta, size_t len, int *argcp,
 		} else {
 			break;
 		}
+		if (ret)
+			return ret;
 		argc--; argv++;
 	}
 
@@ -705,14 +710,14 @@ static int parse_encap_seg6local(struct rtattr *rta, size_t len, int *argcp,
 		srh = parse_srh(segbuf, hmac,
 				action == SEG6_LOCAL_ACTION_END_B6_ENCAP);
 		srhlen = (srh->hdrlen + 1) << 3;
-		rta_addattr_l(rta, len, SEG6_LOCAL_SRH, srh, srhlen);
+		ret = rta_addattr_l(rta, len, SEG6_LOCAL_SRH, srh, srhlen);
 		free(srh);
 	}
 
 	*argcp = argc + 1;
 	*argvp = argv - 1;
 
-	return 0;
+	return ret;
 }
 
 static int parse_encap_mpls(struct rtattr *rta, size_t len,
@@ -730,8 +735,9 @@ static int parse_encap_mpls(struct rtattr *rta, size_t len,
 		exit(1);
 	}
 
-	rta_addattr_l(rta, len, MPLS_IPTUNNEL_DST, &addr.data,
-		      addr.bytelen);
+	if (rta_addattr_l(rta, len, MPLS_IPTUNNEL_DST,
+			  &addr.data, addr.bytelen))
+		return -1;
 
 	argc--;
 	argv++;
@@ -745,7 +751,8 @@ static int parse_encap_mpls(struct rtattr *rta, size_t len,
 				duparg2("ttl", *argv);
 			if (get_u8(&ttl, *argv, 0))
 				invarg("\"ttl\" value is invalid\n", *argv);
-			rta_addattr8(rta, len, MPLS_IPTUNNEL_TTL, ttl);
+			if (rta_addattr8(rta, len, MPLS_IPTUNNEL_TTL, ttl))
+				return -1;
 		} else {
 			break;
 		}
@@ -768,6 +775,7 @@ static int parse_encap_ip(struct rtattr *rta, size_t len,
 	int id_ok = 0, dst_ok = 0, tos_ok = 0, ttl_ok = 0;
 	char **argv = *argvp;
 	int argc = *argcp;
+	int ret = 0;
 
 	while (argc > 0) {
 		if (strcmp(*argv, "id") == 0) {
@@ -778,7 +786,7 @@ static int parse_encap_ip(struct rtattr *rta, size_t len,
 				duparg2("id", *argv);
 			if (get_be64(&id, *argv, 0))
 				invarg("\"id\" value is invalid\n", *argv);
-			rta_addattr64(rta, len, LWTUNNEL_IP_ID, id);
+			ret = rta_addattr64(rta, len, LWTUNNEL_IP_ID, id);
 		} else if (strcmp(*argv, "dst") == 0) {
 			inet_prefix addr;
 
@@ -786,8 +794,8 @@ static int parse_encap_ip(struct rtattr *rta, size_t len,
 			if (dst_ok++)
 				duparg2("dst", *argv);
 			get_addr(&addr, *argv, AF_INET);
-			rta_addattr_l(rta, len, LWTUNNEL_IP_DST,
-				      &addr.data, addr.bytelen);
+			ret = rta_addattr_l(rta, len, LWTUNNEL_IP_DST,
+					    &addr.data, addr.bytelen);
 		} else if (strcmp(*argv, "tos") == 0) {
 			__u32 tos;
 
@@ -796,7 +804,7 @@ static int parse_encap_ip(struct rtattr *rta, size_t len,
 				duparg2("tos", *argv);
 			if (rtnl_dsfield_a2n(&tos, *argv))
 				invarg("\"tos\" value is invalid\n", *argv);
-			rta_addattr8(rta, len, LWTUNNEL_IP_TOS, tos);
+			ret = rta_addattr8(rta, len, LWTUNNEL_IP_TOS, tos);
 		} else if (strcmp(*argv, "ttl") == 0) {
 			__u8 ttl;
 
@@ -805,10 +813,12 @@ static int parse_encap_ip(struct rtattr *rta, size_t len,
 				duparg2("ttl", *argv);
 			if (get_u8(&ttl, *argv, 0))
 				invarg("\"ttl\" value is invalid\n", *argv);
-			rta_addattr8(rta, len, LWTUNNEL_IP_TTL, ttl);
+			ret = rta_addattr8(rta, len, LWTUNNEL_IP_TTL, ttl);
 		} else {
 			break;
 		}
+		if (ret)
+			break;
 		argc--; argv++;
 	}
 
@@ -819,7 +829,7 @@ static int parse_encap_ip(struct rtattr *rta, size_t len,
 	*argcp = argc + 1;
 	*argvp = argv - 1;
 
-	return 0;
+	return ret;
 }
 
 static int parse_encap_ila(struct rtattr *rta, size_t len,
@@ -828,6 +838,7 @@ static int parse_encap_ila(struct rtattr *rta, size_t len,
 	__u64 locator;
 	int argc = *argcp;
 	char **argv = *argvp;
+	int ret = 0;
 
 	if (get_addr64(&locator, *argv) < 0) {
 		fprintf(stderr, "Bad locator: %s\n", *argv);
@@ -836,7 +847,8 @@ static int parse_encap_ila(struct rtattr *rta, size_t len,
 
 	argc--; argv++;
 
-	rta_addattr64(rta, 1024, ILA_ATTR_LOCATOR, locator);
+	if (rta_addattr64(rta, 1024, ILA_ATTR_LOCATOR, locator))
+		return -1;
 
 	while (argc > 0) {
 		if (strcmp(*argv, "csum-mode") == 0) {
@@ -849,8 +861,8 @@ static int parse_encap_ila(struct rtattr *rta, size_t len,
 				invarg("\"csum-mode\" value is invalid\n",
 				       *argv);
 
-			rta_addattr8(rta, 1024, ILA_ATTR_CSUM_MODE,
-				     (__u8)csum_mode);
+			ret = rta_addattr8(rta, 1024, ILA_ATTR_CSUM_MODE,
+					   (__u8)csum_mode);
 
 			argc--; argv++;
 		} else if (strcmp(*argv, "ident-type") == 0) {
@@ -863,8 +875,8 @@ static int parse_encap_ila(struct rtattr *rta, size_t len,
 				invarg("\"ident-type\" value is invalid\n",
 				       *argv);
 
-			rta_addattr8(rta, 1024, ILA_ATTR_IDENT_TYPE,
-				     (__u8)ident_type);
+			ret = rta_addattr8(rta, 1024, ILA_ATTR_IDENT_TYPE,
+					   (__u8)ident_type);
 
 			argc--; argv++;
 		} else if (strcmp(*argv, "hook-type") == 0) {
@@ -877,13 +889,15 @@ static int parse_encap_ila(struct rtattr *rta, size_t len,
 				invarg("\"hook-type\" value is invalid\n",
 				       *argv);
 
-			rta_addattr8(rta, 1024, ILA_ATTR_HOOK_TYPE,
-				     (__u8)hook_type);
+			ret = rta_addattr8(rta, 1024, ILA_ATTR_HOOK_TYPE,
+					   (__u8)hook_type);
 
 			argc--; argv++;
 		} else {
 			break;
 		}
+		if (ret)
+			break;
 	}
 
 	/* argv is currently the first unparsed argument,
@@ -893,7 +907,7 @@ static int parse_encap_ila(struct rtattr *rta, size_t len,
 	*argcp = argc + 1;
 	*argvp = argv - 1;
 
-	return 0;
+	return ret;
 }
 
 static int parse_encap_ip6(struct rtattr *rta, size_t len,
@@ -902,6 +916,7 @@ static int parse_encap_ip6(struct rtattr *rta, size_t len,
 	int id_ok = 0, dst_ok = 0, tos_ok = 0, ttl_ok = 0;
 	char **argv = *argvp;
 	int argc = *argcp;
+	int ret = 0;
 
 	while (argc > 0) {
 		if (strcmp(*argv, "id") == 0) {
@@ -912,7 +927,7 @@ static int parse_encap_ip6(struct rtattr *rta, size_t len,
 				duparg2("id", *argv);
 			if (get_be64(&id, *argv, 0))
 				invarg("\"id\" value is invalid\n", *argv);
-			rta_addattr64(rta, len, LWTUNNEL_IP6_ID, id);
+			ret = rta_addattr64(rta, len, LWTUNNEL_IP6_ID, id);
 		} else if (strcmp(*argv, "dst") == 0) {
 			inet_prefix addr;
 
@@ -920,8 +935,8 @@ static int parse_encap_ip6(struct rtattr *rta, size_t len,
 			if (dst_ok++)
 				duparg2("dst", *argv);
 			get_addr(&addr, *argv, AF_INET6);
-			rta_addattr_l(rta, len, LWTUNNEL_IP6_DST,
-				      &addr.data, addr.bytelen);
+			ret = rta_addattr_l(rta, len, LWTUNNEL_IP6_DST,
+					    &addr.data, addr.bytelen);
 		} else if (strcmp(*argv, "tc") == 0) {
 			__u32 tc;
 
@@ -930,7 +945,7 @@ static int parse_encap_ip6(struct rtattr *rta, size_t len,
 				duparg2("tc", *argv);
 			if (rtnl_dsfield_a2n(&tc, *argv))
 				invarg("\"tc\" value is invalid\n", *argv);
-			rta_addattr8(rta, len, LWTUNNEL_IP6_TC, tc);
+			ret = rta_addattr8(rta, len, LWTUNNEL_IP6_TC, tc);
 		} else if (strcmp(*argv, "hoplimit") == 0) {
 			__u8 hoplimit;
 
@@ -940,10 +955,13 @@ static int parse_encap_ip6(struct rtattr *rta, size_t len,
 			if (get_u8(&hoplimit, *argv, 0))
 				invarg("\"hoplimit\" value is invalid\n",
 				       *argv);
-			rta_addattr8(rta, len, LWTUNNEL_IP6_HOPLIMIT, hoplimit);
+			ret = rta_addattr8(rta, len, LWTUNNEL_IP6_HOPLIMIT,
+					   hoplimit);
 		} else {
 			break;
 		}
+		if (ret)
+			break;
 		argc--; argv++;
 	}
 
@@ -954,7 +972,7 @@ static int parse_encap_ip6(struct rtattr *rta, size_t len,
 	*argcp = argc + 1;
 	*argvp = argv - 1;
 
-	return 0;
+	return ret;
 }
 
 static void lwt_bpf_usage(void)
@@ -1021,6 +1039,7 @@ int lwt_parse_encap(struct rtattr *rta, size_t len, int *argcp, char ***argvp)
 	int argc = *argcp;
 	char **argv = *argvp;
 	__u16 type;
+	int ret = 0;
 
 	NEXT_ARG();
 	type = read_encap_type(*argv);
@@ -1037,37 +1056,40 @@ int lwt_parse_encap(struct rtattr *rta, size_t len, int *argcp, char ***argvp)
 	nest = rta_nest(rta, 1024, RTA_ENCAP);
 	switch (type) {
 	case LWTUNNEL_ENCAP_MPLS:
-		parse_encap_mpls(rta, len, &argc, &argv);
+		ret = parse_encap_mpls(rta, len, &argc, &argv);
 		break;
 	case LWTUNNEL_ENCAP_IP:
-		parse_encap_ip(rta, len, &argc, &argv);
+		ret = parse_encap_ip(rta, len, &argc, &argv);
 		break;
 	case LWTUNNEL_ENCAP_ILA:
-		parse_encap_ila(rta, len, &argc, &argv);
+		ret = parse_encap_ila(rta, len, &argc, &argv);
 		break;
 	case LWTUNNEL_ENCAP_IP6:
-		parse_encap_ip6(rta, len, &argc, &argv);
+		ret = parse_encap_ip6(rta, len, &argc, &argv);
 		break;
 	case LWTUNNEL_ENCAP_BPF:
 		if (parse_encap_bpf(rta, len, &argc, &argv) < 0)
 			exit(-1);
 		break;
 	case LWTUNNEL_ENCAP_SEG6:
-		parse_encap_seg6(rta, len, &argc, &argv);
+		ret = parse_encap_seg6(rta, len, &argc, &argv);
 		break;
 	case LWTUNNEL_ENCAP_SEG6_LOCAL:
-		parse_encap_seg6local(rta, len, &argc, &argv);
+		ret = parse_encap_seg6local(rta, len, &argc, &argv);
 		break;
 	default:
 		fprintf(stderr, "Error: unsupported encap type\n");
 		break;
 	}
+	if (ret)
+		return ret;
+
 	rta_nest_end(rta, nest);
 
-	rta_addattr16(rta, 1024, RTA_ENCAP_TYPE, type);
+	ret = rta_addattr16(rta, 1024, RTA_ENCAP_TYPE, type);
 
 	*argcp = argc;
 	*argvp = argv;
 
-	return 0;
+	return ret;
 }
-- 
2.18.0