nvmet-auth: fix out-of-bounds write in nvmet_auth_challenge()

In the Linux kernel, the following vulnerability has been resolved:

nvmet-auth: fix out-of-bounds write in nvmet_auth_challenge()

nvmet_auth_challenge() receives its output buffer as a void pointer.
sizeof(*d) therefore evaluates to one with GCC and undercounts the fixed
challenge header by 15 bytes. A short AUTH_RECEIVE buffer can pass the
check before the challenge is copied past the end of its allocation.

Use the typed challenge pointer when calculating the response size.

BUG: KASAN: slab-out-of-bounds in nvmet_execute_auth_receive (drivers/nvme/target/fabrics-cmd-auth.c:442 drivers/nvme/target/fabrics-cmd-auth.c:569)
Write of size 32 by task kworker/1:1H/64
Workqueue: nvmet_tcp_wq nvmet_tcp_io_work
Call Trace:
nvmet_execute_auth_receive (drivers/nvme/target/fabrics-cmd-auth.c:442 drivers/nvme/target/fabrics-cmd-auth.c:569)
nvmet_tcp_try_recv_pdu (drivers/nvme/target/tcp.c:1119 drivers/nvme/target/tcp.c:1243)
nvmet_tcp_io_work (drivers/nvme/target/tcp.c:1350 drivers/nvme/target/tcp.c:1382 drivers/nvme/target/tcp.c:1445)
process_one_work (kernel/workqueue.c:3322)
worker_thread (kernel/workqueue.c:3405 kernel/workqueue.c:3486)
kthread (kernel/kthread.c:436)
ret_from_fork (arch/x86/kernel/process.c:158)
ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
The buggy address is located 16 bytes inside of
allocated 33-byte region [ffff888000554e80, ffff888000554ea1)
Kernel panic - not syncing: KASAN: panic_on_warn set ...