[PATCH 4/4 nf] netfilter: xtables: fix L4 header parsing for non-first fragments

[Fernando Fernandez Mancera <fmancera@suse.de>]

The TPROXY target and osf match relies on L4 header to operate. For
fragmented packets, every fragment carries the transport protocol
identifier, but only the first fragment contains the L4 header.

As the 'raw' table can be configured to run at priority -450 (before
defragmentation at -400), the target/match can be reached before
reassembly. In this case, non-first fragments have their payload
incorrectly parsed as a TCP/UDP header.

Add a fragment check to ensure TPROXY/osf only evaluates unfragmented
packets or the first fragment in the stream.

Fixes: 902d6a4c2a4f ("netfilter: nf_defrag: Skip defrag if NOTRACK is set")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/netfilter/xt_TPROXY.c | 8 ++++++--
 net/netfilter/xt_osf.c    | 3 +++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/xt_TPROXY.c b/net/netfilter/xt_TPROXY.c
index e4bea1d346cf..ac4b011ce48c 100644
--- a/net/netfilter/xt_TPROXY.c
+++ b/net/netfilter/xt_TPROXY.c
@@ -40,6 +40,9 @@ tproxy_tg4(struct net *net, struct sk_buff *skb, __be32 laddr, __be16 lport,
 	struct udphdr _hdr, *hp;
 	struct sock *sk;
 
+	if (ip_is_fragment(iph))
+		return NF_DROP;
+
 	hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
 	if (hp == NULL)
 		return NF_DROP;
@@ -106,6 +109,7 @@ tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
+	unsigned short fragoff = 0;
 	struct udphdr _hdr, *hp;
 	struct sock *sk;
 	const struct in6_addr *laddr;
@@ -113,8 +117,8 @@ tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
 	int thoff = 0;
 	int tproto;
 
-	tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
-	if (tproto < 0)
+	tproto = ipv6_find_hdr(skb, &thoff, -1, &fragoff, NULL);
+	if (tproto < 0 || fragoff)
 		return NF_DROP;
 
 	hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
diff --git a/net/netfilter/xt_osf.c b/net/netfilter/xt_osf.c
index dc9485854002..889dff4daff0 100644
--- a/net/netfilter/xt_osf.c
+++ b/net/netfilter/xt_osf.c
@@ -27,6 +27,9 @@
 static bool
 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
 {
+	if (ip_is_fragment(ip_hdr(skb)))
+		return false;
+
 	return nf_osf_match(skb, xt_family(p), xt_hooknum(p), xt_in(p),
 			    xt_out(p), p->matchinfo, xt_net(p), nf_osf_fingers);
 }
-- 
2.53.0