icmp: fix icmp_ext_echo_iio parsing in icmp_build_probe

In icmp_build_probe(), the icmp_ext_echo_iio parsing should be done
step by step and skb_header_pointer() return value should always be
checked, this patch fixes 3 places in there:

  - On case ICMP_EXT_ECHO_CTYPE_NAME, it should only copy ident.name
    from skb by skb_header_pointer(), its len is ident_len. Besides,
    the return value of skb_header_pointer() should always be checked.

  - On case ICMP_EXT_ECHO_CTYPE_INDEX, move ident_len check ahead of
    skb_header_pointer(), and also do the return value check for
    skb_header_pointer().

  - On case ICMP_EXT_ECHO_CTYPE_ADDR, before accessing iio->ident.addr.
    ctype3_hdr.addrlen, skb_header_pointer() should be called first,
    then check its return value and ident_len.
    On subcases ICMP_AFI_IP and ICMP_AFI_IP6, also do check for ident.
    addr.ctype3_hdr.addrlen and skb_header_pointer()'s return value.
    On subcase ICMP_AFI_IP, the len for skb_header_pointer() should be
    "sizeof(iio->extobj_hdr) + sizeof(iio->ident.addr.ctype3_hdr) +
    sizeof(struct in_addr)" or "ident_len".

v1->v2:
  - To make it more clear, call skb_header_pointer() once only for
    iio->indent's parsing as Jakub Suggested.
v2->v3:
  - The extobj_hdr.length check against sizeof(_iio) should be done
    before calling skb_header_pointer(), as Eric noticed.

Fixes: d329ea5b ("icmp: add response to RFC 8335 PROBE messages")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/31628dd76657ea62f5cf78bb55da6b35240831f1.1634205050.git.lucien.xin@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/icmp.c

@@ -1054,14 +1054,19 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
 	iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr), &_iio);
 	if (!ext_hdr || !iio)
 		goto send_mal_query;
-	if (ntohs(iio->extobj_hdr.length) <= sizeof(iio->extobj_hdr))
+	if (ntohs(iio->extobj_hdr.length) <= sizeof(iio->extobj_hdr) ||
+	    ntohs(iio->extobj_hdr.length) > sizeof(_iio))
 		goto send_mal_query;
 	ident_len = ntohs(iio->extobj_hdr.length) - sizeof(iio->extobj_hdr);
+	iio = skb_header_pointer(skb, sizeof(_ext_hdr),
+				 sizeof(iio->extobj_hdr) + ident_len, &_iio);
+	if (!iio)
+		goto send_mal_query;
+
 	status = 0;
 	dev = NULL;
 	switch (iio->extobj_hdr.class_type) {
 	case ICMP_EXT_ECHO_CTYPE_NAME:
-		iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
 		if (ident_len >= IFNAMSIZ)
 			goto send_mal_query;
 		memset(buff, 0, sizeof(buff));
@@ -1069,30 +1074,24 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
 		dev = dev_get_by_name(net, buff);
 		break;
 	case ICMP_EXT_ECHO_CTYPE_INDEX:
-		iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
-					 sizeof(iio->ident.ifindex), &_iio);
 		if (ident_len != sizeof(iio->ident.ifindex))
 			goto send_mal_query;
 		dev = dev_get_by_index(net, ntohl(iio->ident.ifindex));
 		break;
 	case ICMP_EXT_ECHO_CTYPE_ADDR:
-		if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
+		if (ident_len < sizeof(iio->ident.addr.ctype3_hdr) ||
+		    ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
 				 iio->ident.addr.ctype3_hdr.addrlen)
 			goto send_mal_query;
 		switch (ntohs(iio->ident.addr.ctype3_hdr.afi)) {
 		case ICMP_AFI_IP:
-			iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
-						 sizeof(struct in_addr), &_iio);
-			if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
-					 sizeof(struct in_addr))
+			if (iio->ident.addr.ctype3_hdr.addrlen != sizeof(struct in_addr))
 				goto send_mal_query;
 			dev = ip_dev_find(net, iio->ident.addr.ip_addr.ipv4_addr);
 			break;
 #if IS_ENABLED(CONFIG_IPV6)
 		case ICMP_AFI_IP6:
-			iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
-			if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
-					 sizeof(struct in6_addr))
+			if (iio->ident.addr.ctype3_hdr.addrlen != sizeof(struct in6_addr))
 				goto send_mal_query;
 			dev = ipv6_stub->ipv6_dev_find(net, &iio->ident.addr.ip_addr.ipv6_addr, dev);
 			dev_hold(dev);