If a socket is processing ioctl 'NBD_SET_SOCK', config->socks might be
krealloc in nbd_add_socket(), and a garbage request is received now, a UAF
may occurs.

  T1
  nbd_ioctl
   __nbd_ioctl
    nbd_add_socket
     blk_mq_freeze_queue
				T2
  				recv_work
  				 nbd_read_reply
  				  sock_xmit
     krealloc config->socks
				   def config->socks

Pass nbd_sock to nbd_read_reply(). And introduce a new function
sock_xmit_recv(), which differs from sock_xmit only in the way it get
socket.

==================================================================
BUG: KASAN: use-after-free in sock_xmit+0x525/0x550
Read of size 8 at addr ffff8880188ec428 by task kworker/u12:1/18779

Workqueue: knbd4-recv recv_work
Call Trace:
 __dump_stack
 dump_stack+0xbe/0xfd
 print_address_description.constprop.0+0x19/0x170
 __kasan_report.cold+0x6c/0x84
 kasan_report+0x3a/0x50
 sock_xmit+0x525/0x550
 nbd_read_reply+0xfe/0x2c0
 recv_work+0x1c2/0x750
 process_one_work+0x6b6/0xf10
 worker_thread+0xdd/0xd80
 kthread+0x30a/0x410
 ret_from_fork+0x22/0x30

Allocated by task 18784:
 kasan_save_stack+0x1b/0x40
 kasan_set_track
 set_alloc_info
 __kasan_kmalloc
 __kasan_kmalloc.constprop.0+0xf0/0x130
 slab_post_alloc_hook
 slab_alloc_node
 slab_alloc
 __kmalloc_track_caller+0x157/0x550
 __do_krealloc
 krealloc+0x37/0xb0
 nbd_add_socket
 +0x2d3/0x880
 __nbd_ioctl
 nbd_ioctl+0x584/0x8e0
 __blkdev_driver_ioctl
 blkdev_ioctl+0x2a0/0x6e0
 block_ioctl+0xee/0x130
 vfs_ioctl
 __do_sys_ioctl
 __se_sys_ioctl+0x138/0x190
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x61/0xc6

Freed by task 18784:
 kasan_save_stack+0x1b/0x40
 kasan_set_track+0x1c/0x30
 kasan_set_free_info+0x20/0x40
 __kasan_slab_free.part.0+0x13f/0x1b0
 slab_free_hook
 slab_free_freelist_hook
 slab_free
 kfree+0xcb/0x6c0
 krealloc+0x56/0xb0
 nbd_add_socket+0x2d3/0x880
 __nbd_ioctl
 nbd_ioctl+0x584/0x8e0
 __blkdev_driver_ioctl
 blkdev_ioctl+0x2a0/0x6e0
 block_ioctl+0xee/0x130
 vfs_ioctl
 __do_sys_ioctl
 __se_sys_ioctl+0x138/0x190
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x61/0xc6
Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230911023308.3467802-1-linan666@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>