CHECKSUM_PARTIAL skbs should never arrive in ip_fragment. If we get one
of those warn about them once and handle them gracefully by recalculating
the checksum.

Fixes: commit 32dce968dd987 ("ipv6: Allow for partial checksums on non-ufo 
packets")
See-also: commit 72e843bb09d45 ("ipv6: ip6_fragment() should check 
CHECKSUM_PARTIAL")
Cc: Eric Dumazet <eduma...@google.com>
Cc: Vlad Yasevich <vyasev...@gmail.com>
Cc: Benjamin Coddington <bcodd...@redhat.com>
Cc: Tom Herbert <t...@herbertland.com>
Signed-off-by: Hannes Frederic Sowa <han...@stressinduktion.org>
---
 net/ipv6/ip6_output.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 9828a71..c6c5630 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -605,6 +605,10 @@ int ip6_fragment(struct net *net, struct sock *sk, struct 
sk_buff *skb,
        frag_id = ipv6_select_ident(net, &ipv6_hdr(skb)->daddr,
                                    &ipv6_hdr(skb)->saddr);
 
+       if (WARN_ON_ONCE(skb->ip_summed == CHECKSUM_PARTIAL) &&
+           (err = skb_checksum_help(skb)))
+               goto fail;
+
        hroom = LL_RESERVED_SPACE(rt->dst.dev);
        if (skb_has_frag_list(skb)) {
                int first_len = skb_pagelen(skb);
@@ -733,10 +737,6 @@ slow_path_clean:
        }
 
 slow_path:
-       if ((skb->ip_summed == CHECKSUM_PARTIAL) &&
-           skb_checksum_help(skb))
-               goto fail;
-
        left = skb->len - hlen;         /* Space per frame */
        ptr = hlen;                     /* Where to start from */
 
-- 
2.5.0

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