netdev - [PATCH 2/2] ipv6: don't deliver packets with zero length to raw sockets

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Date:   Fri, 21 Apr 2017 13:58:44 +1000
From:   Jamie Bainbridge <jbainbri@...hat.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Cc:     Jamie Bainbridge <jbainbri@...hat.com>
Subject: [PATCH 2/2] ipv6: don't deliver packets with zero length to raw sockets

IPv6 assumes there is data after the network header and blindly delivers
skbs to raw sockets without checking the presence of data.

With an application in a common loop where it checks select/poll/epoll
then ioctl(SIOCINQ/FIONREAD) is positive before continuing to
recvfrom(), this behaviour can cause the application to loop forever
on ioctl() because there is a zero-length skb to receive.

With this, it is very easy to make a Denial of Service attack by
crafting a packet which declares a Next Header in the IPv6 header but
does not actually supply a transport header and/or payload.

skb->len is already correctly set in ip6_input_finish() with pskb_pull()
so check this length before delivering zero data to raw sockets.

Signed-off-by: Jamie Bainbridge <jbainbri@...hat.com>
---
 net/ipv6/raw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 0da6a12b5472e322d679572c7244e5c9bc467741..29dfdcefe1cc5f4c082ed919026e49e70320605e 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -174,7 +174,7 @@ static bool ipv6_raw_deliver(struct sk_buff *skb, int nexthdr)
 	read_lock(&raw_v6_hashinfo.lock);
 	sk = sk_head(&raw_v6_hashinfo.ht[hash]);

-	if (!sk)
+	if (!sk || !(skb->len))
 		goto out;

 	net = dev_net(skb->dev);
-- 
1.8.3.1