nbd: always initialize struct msghdr completely

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nbd: always initialize struct msghdr completely syzbot complains that msg->msg_get_inq value can be uninitialized [1] struct msghdr got many new fields recently, we should always make sure their values is zero by default. [1] BUG: KMSAN: uninit-value in tcp_recvmsg+0x686/0xac0 net/ipv4/tcp.c:2571 tcp_recvmsg+0x686/0xac0 net/ipv4/tcp.c:2571 inet_recvmsg+0x131/0x580 net/ipv4/af_inet.c:879 sock_recvmsg_nosec net/socket.c:1044 [inline] sock_recvmsg+0x12b/0x1e0 net/socket.c:1066 __sock_xmit+0x236/0x5c0 drivers/block/nbd.c:538 nbd_read_reply drivers/block/nbd.c:732 [inline] recv_work+0x262/0x3100 drivers/block/nbd.c:863 process_one_work kernel/workqueue.c:2627 [inline] process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2700 worker_thread+0xf45/0x1490 kernel/workqueue.c:2781 kthread+0x3ed/0x540 kernel/kthread.c:388 ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242 Local variable msg created at: __sock_xmit+0x4c/0x5c0 drivers/block/nbd.c:513 nbd_read_reply drivers/block/nbd.c:732 [inline] recv_work+0x262/0x3100 drivers/block/nbd.c:863 CPU: 1 PID: 7465 Comm: kworker/u5:1 Not tainted 6.7.0-rc7-syzkaller-00041-gf016f7547aee #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023 Workqueue: nbd5-recv recv_work

References

• https://git.kernel.org/stable/c/d9c54763e5cdbbd3f81868597fe8aca3c96e6387
• https://git.kernel.org/stable/c/1960f2b534da1e6c65fb96f9e98bda773495f406
• https://git.kernel.org/stable/c/b0028f333420a65a53a63978522db680b37379dd
• https://git.kernel.org/stable/c/78fbb92af27d0982634116c7a31065f24d092826