vxlan: validate ND option lengths in vxlan_na_create

vxlan: validate ND option lengths in vxlan_na_create

vxlan_na_create() walks ND options according to option-provided
lengths. A malformed option can make the parser advance beyond the
computed option span or use a too-short source LLADDR option payload.

Validate option lengths against the remaining NS option area before
advancing, and only read source LLADDR when the option is large enough
for an Ethernet address.

Fixes: 4b29dba9c085 ("vxlan: fix nonfunctional neigh_reduce()")
Cc: stable@vger.kernel.org
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Tested-by: Ao Zhou <n05ec@lzu.edu.cn>
Co-developed-by: Yuan Tan <tanyuan98@outlook.com>
Signed-off-by: Yuan Tan <tanyuan98@outlook.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Yang Yang <n05ec@lzu.edu.cn>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20260326034441.2037420-4-n05ec@lzu.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>