netdev - PATCH [1/1] ipv4: Prevent malformed UFO fragments in ip_append

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Message-ID: <6A051441C8B95A448E49718A747690B901CA76C741@gbplmail03.genband.com>
Date:	Fri, 10 Jun 2016 19:21:26 +0000
From:	Steven Caron <steven.caron@...band.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Cong Wang <xiyou.wangcong@...il.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Linux Kernel Network Developers" <netdev@...r.kernel.org>,
	Steven Caron <steven.caron@...band.com>
Subject: PATCH [1/1] ipv4: Prevent malformed UFO fragments in ip_append_page

As  the ip fragment offset field counts 8-byte chunks, non-final ip
fragments must be multiples of 8 bytes of payload. Depending  on
the mtu and ip option sizes, ip_append_page wasn't respecting this,
notably when running NFS under UDP.

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 124bf0a..21ec54e 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1239,7 +1239,7 @@ ssize_t   ip_append_page(struct sock *sk, struct flowi4 *fl4, struct page *page,
                if (skb->ip_summed != CHECKSUM_PARTIAL)
                        return -EOPNOTSUPP;

-               skb_shinfo(skb)->gso_size = mtu - fragheaderlen;
+               skb_shinfo(skb)->gso_size = maxfraglen - fragheaderlen;
                skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
        }
        cork->length += size;