When ipv6_find_hdr is used to find a fragment header
(caller specifies target NEXTHDR_FRAGMENT) we erronously return
-ENOENT for all fragments with nonzero offset.
Before commit 9195bb8e38, when target was specified, we did not
enter the exthdr walk loop as nexthdr == target so this used to work.
Now we do (so we can skip empty route headers). When we then stumble upon
a frag with nonzero frag_off we must return -ENOENT ("header not found")
only if the caller did not specifically request NEXTHDR_FRAGMENT.
This allows nfables exthdr expression to match ipv6 fragments, e.g. via
nft add rule ip6 filter input frag frag-off gt 0
Fixes: 9195bb8e38 ("ipv6: improve ipv6_find_hdr() to skip empty routing headers")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
5d150a9855