nfsd: widen nfsd_genl_rqstp address fields to sockaddr_storage

Summary

In the Linux kernel, the following vulnerability has been resolved: nfsd: widen nfsd_genl_rqstp address fields to sockaddr_storage struct nfsd_genl_rqstp declares rq_daddr and rq_saddr as plain "struct sockaddr" (16 bytes). When an IPv6 NFS client is connected, nfsd_genl_rpc_status_compose_msg() casts these fields to "struct sockaddr_in6 *" (28 bytes) and reads sin6_addr at offset 8..24, which extends 8 bytes past the end of the 16-byte sockaddr field into the adjacent rq_flags member. The 16-byte nla_put_in6_addr then ships 8 bytes of truncated IPv6 address followed by 8 bytes of rq_flags to userspace via the NFSD_A_RPC_STATUS_SADDR6/DADDR6 netlink attributes. This is reachable by any unprivileged process in the network namespace because NFSD_CMD_RPC_STATUS_GET uses GENL_CMD_CAP_DUMP without GENL_ADMIN_PERM. Fix by widening rq_daddr and rq_saddr to struct sockaddr_storage so the IPv6 casts operate within bounds, copying sizeof(struct sockaddr_storage) bytes in the memcpy calls so the full address is captured, and zero-initializing the genl_rqstp stack variable to prevent leaking uninitialized tail bytes through netlink.