ipv6/exthdrs: strict Pad1 and PadN check

The following tightens the padding check from commit
c1412fce7eccae62b4de22494f6ab3ff8a90c0c6 :

* Take into account combinations of consecutive Pad1 and PadN.

* Catch the corner case of when only padding is present in the
  header, when the extention header length is 0 (i.e., 8 bytes).
  In this case, the header would have exactly 6 bytes of padding:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
:  Next Header  : Hdr Ext Len=0 :                               :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
:                        Padding (Pad1 or PadN)                 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Signed-off-by: Eldad Zack <eldad@fogrefinery.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 1 deletions

diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 50ec95f9aeeb..6447dc49429f 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -144,6 +144,7 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
         const unsigned char *nh = skb_network_header(skb);
         int off = skb_network_header_len(skb);
         int len = (skb_transport_header(skb)[1] + 1) << 3;
+        int padlen = 0;
 
         if (skb_transport_offset(skb) + len > skb_headlen(skb))
                 goto bad;
@@ -158,6 +159,9 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
                 switch (nh[off]) {
                 case IPV6_TLV_PAD1:
                         optlen = 1;
+                        padlen++;
+                        if (padlen > 7)
+                                goto bad;
                         break;
 
                 case IPV6_TLV_PADN:
@@ -166,7 +170,8 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
                          * of 8. 7 is therefore the highest valid value.
                          * See also RFC 4942, Section 2.1.9.5.
                          */
-                        if (optlen > 7)
+                        padlen += optlen;
+                        if (padlen > 7)
                                 goto bad;
                         /* RFC 4942 recommends receiving hosts to
                          * actively check PadN payload to contain
@@ -195,11 +200,19 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
                                 if (ip6_tlvopt_unknown(skb, off) == 0)
                                         return false;
                         }
+                        padlen = 0;
                         break;
                 }
                 off += optlen;
                 len -= optlen;
         }
+        /* This case will not be caught by above check since its padding
+         * length is smaller than 7:
+         * 1 byte NH + 1 byte Length + 6 bytes Padding
+         */
+        if ((padlen == 6) && ((off - skb_network_header_len(skb)) == 8))
+                goto bad;
+
         if (len == 0)
                 return true;
 bad: