Fix two further potential unbounded recursions in GUE error handlers

Patch 1/2 takes care of preventing the issue fixed by commit 11789039da53 ("fou: Prevent unbounded recursion in GUE error handler") also with UDP-Lite payloads -- I just realised this might happen from a syzbot report.

Patch 2/2 fixes the issue for both UDP and UDP-Lite on IPv6, which I also forgot to deal with in that same commit.

Stefano Brivio (2):
fou: Prevent unbounded recursion in GUE error handler also with
UDP-Lite
fou6: Prevent unbounded recursion in GUE error handler

 net/ipv4/fou.c  | 3 ++-
 net/ipv6/fou6.c | 8 ++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

2.20.1

In commit 11789039da53 ("fou: Prevent unbounded recursion in GUE error handler"), I didn't take care of the case where UDP-Lite is encapsulated into UDP or UDP-Lite with GUE. From a syzbot report about a possibly similar issue with GUE on IPv6, I just realised the same thing might happen with a UDP-Lite inner payload.

Also skip exception handling for inner UDP-Lite protocol.

---
 net/ipv4/fou.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index 0c9f171fb085..632863541082 100644
@@ -1065,7 +1065,8 @@ static int gue_err(struct sk_buff *skb, u32 info)
 	 * recursion. Besides, this kind of encapsulation can't even be
 	 * configured currently. Discard this.
 	 */
-	if (guehdr->proto_ctype == IPPROTO_UDP)
+	if (guehdr->proto_ctype == IPPROTO_UDP ||
+	    guehdr->proto_ctype == IPPROTO_UDPLITE)
 		return -EOPNOTSUPP;
 
 	skb_set_transport_header(skb, -(int)sizeof(struct icmphdr));

2.20.1

I forgot to deal with IPv6 in commit 11789039da53 ("fou: Prevent unbounded recursion in GUE error handler").

Now syzbot reported what might be the same type of issue, caused by gue6_err(), that is, handling exceptions for direct UDP encapsulation in GUE (UDP-in-UDP) leads to unbounded recursion in the GUE exception handler.

As it probably doesn't make sense to set up GUE this way, and it's currently not even possible to configure this, skip exception handling for UDP (or UDP-Lite) packets encapsulated in UDP (or UDP-Lite) packets with GUE on IPv6.

---
 net/ipv6/fou6.c | 8 ++++++++
 1 file changed, 8 insertions(+)

index bd675c61deb1..7da7bf3b7fe3 100644
@@ -131,6 +131,14 @@ static int gue6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 	if (validate_gue_flags(guehdr, optlen))
 		return -EINVAL;
 
+	/* Handling exceptions for direct UDP encapsulation in GUE would lead to
+	 * recursion. Besides, this kind of encapsulation can't even be
+	 * configured currently. Discard this.
+	 */
+	if (guehdr->proto_ctype == IPPROTO_UDP ||
+	    guehdr->proto_ctype == IPPROTO_UDPLITE)
+		return -EOPNOTSUPP;
+
 	skb_set_transport_header(skb, -(int)sizeof(struct icmp6hdr));
 	ret = gue6_err_proto_handler(guehdr->proto_ctype, skb,
 				     opt, type, code, offset, info);

2.20.1

From: Stefano Brivio <[email protected]>
Date: Thu, 3 Jan 2019 21:43:33 +0100

Series applied, thanks.