[PATCH v1 1/1] ipv4: Prevent malformed UFO fragments in ip_append_page

[Steven Caron]

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.

Signed-off-by: Steven Caron <steven.caron@xxxxxxxxxxx>
---
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;