Describe CVE-2021-47078.
What is CVE-2021-47078?
In the Linux kernel, the following vulnerability has been resolved:

RDMA/rxe: Clear all QP fields if creation failed

rxe_qp_do_cleanup() relies on valid pointer values in QP for the properly
created ones, but in case rxe_qp_from_init() failed it was filled with
garbage and caused tot the following error.

  refcount_t: underflow; use-after-free.
  WARNING: CPU: 1 PID: 12560 at lib/refcount.c:28 refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
  Modules linked in:
  CPU: 1 PID: 12560 Comm: syz-executor.4 Not tainted 5.12.0-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  RIP: 0010:refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
  Code: e9 db fe ff ff 48 89 df e8 2c c2 ea fd e9 8a fe ff ff e8 72 6a a7 fd 48 c7 c7 e0 b2 c1 89 c6 05 dc 3a e6 09 01 e8 ee 74 fb 04 <0f> 0b e9 af fe ff ff 0f 1f 84 00 00 00 00 00 41 56 41 55 41 54 55
  RSP: 0018:ffffc900097ceba8 EFLAGS: 00010286
  RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
  RDX: 0000000000040000 RSI: ffffffff815bb075 RDI: fffff520012f9d67
  RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
  R10: ffffffff815b4eae R11: 0000000000000000 R12: ffff8880322a4800
  R13: ffff8880322a4940 R14: ffff888033044e00 R15: 0000000000000000
  FS:  00007f6eb2be3700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007fdbe5d41000 CR3: 000000001d181000 CR4: 00000000001506e0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   __refcount_sub_and_test include/linux/refcount.h:283 [inline]
   __refcount_dec_and_test include/linux/refcount.h:315 [inline]
   refcount_dec_and_test include/linux/refcount.h:333 [inline]
   kref_put include/linux/kref.h:64 [inline]
   rxe_qp_do_cleanup+0x96f/0xaf0 drivers/infiniband/sw/rxe/rxe_qp.c:805
   execute_in_process_context+0x37/0x150 kernel/workqueue.c:3327
   rxe_elem_release+0x9f/0x180 drivers/infiniband/sw/rxe/rxe_pool.c:391
   kref_put include/linux/kref.h:65 [inline]
   rxe_create_qp+0x2cd/0x310 drivers/infiniband/sw/rxe/rxe_verbs.c:425
   _ib_create_qp drivers/infiniband/core/core_priv.h:331 [inline]
   ib_create_named_qp+0x2ad/0x1370 drivers/infiniband/core/verbs.c:1231
   ib_create_qp include/rdma/ib_verbs.h:3644 [inline]
   create_mad_qp+0x177/0x2d0 drivers/infiniband/core/mad.c:2920
   ib_mad_port_open drivers/infiniband/core/mad.c:3001 [inline]
   ib_mad_init_device+0xd6f/0x1400 drivers/infiniband/core/mad.c:3092
   add_client_context+0x405/0x5e0 drivers/infiniband/core/device.c:717
   enable_device_and_get+0x1cd/0x3b0 drivers/infiniband/core/device.c:1331
   ib_register_device drivers/infiniband/core/device.c:1413 [inline]
   ib_register_device+0x7c7/0xa50 drivers/infiniband/core/device.c:1365
   rxe_register_device+0x3d5/0x4a0 drivers/infiniband/sw/rxe/rxe_verbs.c:1147
   rxe_add+0x12fe/0x16d0 drivers/infiniband/sw/rxe/rxe.c:247
   rxe_net_add+0x8c/0xe0 drivers/infiniband/sw/rxe/rxe_net.c:503
   rxe_newlink drivers/infiniband/sw/rxe/rxe.c:269 [inline]
   rxe_newlink+0xb7/0xe0 drivers/infiniband/sw/rxe/rxe.c:250
   nldev_newlink+0x30e/0x550 drivers/infiniband/core/nldev.c:1555
   rdma_nl_rcv_msg+0x36d/0x690 drivers/infiniband/core/netlink.c:195
   rdma_nl_rcv_skb drivers/infiniband/core/netlink.c:239 [inline]
   rdma_nl_rcv+0x2ee/0x430 drivers/infiniband/core/netlink.c:259
   netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
   netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
   netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
   sock_sendmsg_nosec net/socket.c:654 [inline]
   sock_sendmsg+0xcf/0x120 net/socket.c:674
   ____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
   ___sys_sendmsg+0xf3/0x170 net/socket.c:2404
   __sys_sendmsg+0xe5/0x1b0 net/socket.c:2433
   do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
   entry_SYSCALL_64_after_hwframe+0
---truncated---.