Commit 44039e00 authored Jan 03, 2019 by Stefano Brivio Committed by David S. Miller Jan 04, 2019

fou6: Prevent unbounded recursion in GUE error handler



I forgot to deal with IPv6 in commit 11789039 ("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.

Reported-by:  <syzbot+4ad25edc7a33e4ab91e0@syzkaller.appspotmail.com>
Reported-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Fixes: b8a51b38 ("fou, fou6: ICMP error handlers for FoU and GUE")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent bc6e019b

net/ipv6/fou6.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -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);

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