ipv6_find_hdr() currently assumes that the next-header field in the
fragment header of the non-first fragment is the "protocol number of
the last header" (here last header excludes any extension header
protocol numbers ) which is incorrect as per RFC2460. The next-header
value is the first header of the fragmentable part of the original
packet (which can be extension header as well).
This can create reassembly problems. For example: Fragmented
authenticated OSPFv3 packets (where AH header is inserted before the
protocol header). For the second fragment, the next header value in
the fragment header will be NEXTHDR_AUTH which is correct but
ipv6_find_hdr will return ENOENT since AH is an extension header
resulting in second fragment getting dropped. This check for the
presence of non-extension header needs to be removed.
Signed-off-by: Rahul Sharma <rsharma@xxxxxxxxxx>