[NETFILTER]: Fix ip6_tables protocol bypass bug
As reported by Mark Dowd <Mark_Dowd@McAfee.com>, ip6_tables is susceptible
to a fragmentation attack causing false negatives on protocol matches.
When the protocol header doesn't follow the fragment header immediately,
the fragment header contains the protocol number of the next extension
header. When the extension header and the protocol header are sent in
a second fragment a rule like "ip6tables .. -p udp -j DROP" will never
match.
Drop fragments that are at offset 0 and don't contain the final protocol
header regardless of the ruleset, since this should not happen normally.
With help from Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 4ab368f..f0328c7 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -111,7 +111,7 @@
const char *outdev,
const struct ip6t_ip6 *ip6info,
unsigned int *protoff,
- int *fragoff)
+ int *fragoff, int *hotdrop)
{
size_t i;
unsigned long ret;
@@ -169,9 +169,11 @@
unsigned short _frag_off;
protohdr = ipv6_find_hdr(skb, protoff, -1, &_frag_off);
- if (protohdr < 0)
+ if (protohdr < 0) {
+ if (_frag_off == 0)
+ *hotdrop = 1;
return 0;
-
+ }
*fragoff = _frag_off;
dprintf("Packet protocol %hi ?= %s%hi.\n",
@@ -290,7 +292,7 @@
IP_NF_ASSERT(e);
IP_NF_ASSERT(back);
if (ip6_packet_match(*pskb, indev, outdev, &e->ipv6,
- &protoff, &offset)) {
+ &protoff, &offset, &hotdrop)) {
struct ip6t_entry_target *t;
if (IP6T_MATCH_ITERATE(e, do_match,