nfsd: under NFSv4.1, fix double svc_xprt_put on rpc_create failure

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

nfsd: under NFSv4.1, fix double svc_xprt_put on rpc_create failure

On error situation `clp->cl_cb_conn.cb_xprt` should not be given
a reference to the xprt otherwise both client cleanup and the
error handling path of the caller call to put it. Better to
delay handing over the reference to a later branch.

[ 72.530665] refcount_t: underflow; use-after-free.
[ 72.531933] WARNING: CPU: 0 PID: 173 at lib/refcount.c:28 refcount_warn_saturate+0xcf/0x120
[ 72.533075] Modules linked in: nfsd(OE) nfsv4(OE) nfsv3(OE) nfs(OE) lockd(OE) compat_nfs_ssc(OE) nfs_acl(OE) rpcsec_gss_krb5(OE) auth_rpcgss(OE) rpcrdma(OE) dns_resolver fscache netfs grace rdma_cm iw_cm ib_cm sunrpc(OE) mlx5_ib mlx5_core mlxfw pci_hyperv_intf ib_uverbs ib_core xt_MASQUERADE nf_conntrack_netlink nft_counter xt_addrtype nft_compat br_netfilter bridge stp llc nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set overlay nf_tables nfnetlink crct10dif_pclmul crc32_pclmul ghash_clmulni_intel xfs serio_raw virtio_net virtio_blk net_failover failover fuse [last unloaded: sunrpc]
[ 72.540389] CPU: 0 PID: 173 Comm: kworker/u16:5 Tainted: G OE 5.15.82-dan #1
[ 72.541511] Hardware name: Red Hat KVM/RHEL-AV, BIOS 1.16.0-3.module+el8.7.0+1084+97b81f61 04/01/2014
[ 72.542717] Workqueue: nfsd4_callbacks nfsd4_run_cb_work [nfsd]
[ 72.543575] RIP: 0010:refcount_warn_saturate+0xcf/0x120
[ 72.544299] Code: 55 00 0f 0b 5d e9 01 50 98 00 80 3d 75 9e 39 08 00 0f 85 74 ff ff ff 48 c7 c7 e8 d1 60 8e c6 05 61 9e 39 08 01 e8 f6 51 55 00 <0f> 0b 5d e9 d9 4f 98 00 80 3d 4b 9e 39 08 00 0f 85 4c ff ff ff 48
[ 72.546666] RSP: 0018:ffffb3f841157cf0 EFLAGS: 00010286
[ 72.547393] RAX: 0000000000000026 RBX: ffff89ac6231d478 RCX: 0000000000000000
[ 72.548324] RDX: ffff89adb7c2c2c0 RSI: ffff89adb7c205c0 RDI: ffff89adb7c205c0
[ 72.549271] RBP: ffffb3f841157cf0 R08: 0000000000000000 R09: c0000000ffefffff
[ 72.550209] R10: 0000000000000001 R11: ffffb3f841157ad0 R12: ffff89ac6231d180
[ 72.551142] R13: ffff89ac6231d478 R14: ffff89ac40c06180 R15: ffff89ac6231d4b0
[ 72.552089] FS: 0000000000000000(0000) GS:ffff89adb7c00000(0000) knlGS:0000000000000000
[ 72.553175] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 72.553934] CR2: 0000563a310506a8 CR3: 0000000109a66000 CR4: 0000000000350ef0
[ 72.554874] Call Trace:
[ 72.555278] <TASK>
[ 72.555614] svc_xprt_put+0xaf/0xe0 [sunrpc]
[ 72.556276] nfsd4_process_cb_update.isra.11+0xb7/0x410 [nfsd]
[ 72.557087] ? update_load_avg+0x82/0x610
[ 72.557652] ? cpuacct_charge+0x60/0x70
[ 72.558212] ? dequeue_entity+0xdb/0x3e0
[ 72.558765] ? queued_spin_unlock+0x9/0x20
[ 72.559358] nfsd4_run_cb_work+0xfc/0x270 [nfsd]
[ 72.560031] process_one_work+0x1df/0x390
[ 72.560600] worker_thread+0x37/0x3b0
[ 72.561644] ? process_one_work+0x390/0x390
[ 72.562247] kthread+0x12f/0x150
[ 72.562710] ? set_kthread_struct+0x50/0x50
[ 72.563309] ret_from_fork+0x22/0x30
[ 72.563818] </TASK>
[ 72.564189] ---[ end trace 031117b1c72ec616 ]---
[ 72.566019] list_add corruption. next->prev should be prev (ffff89ac4977e538), but was ffff89ac4763e018. (next=ffff89ac4763e018).
[ 72.567647] ------------[ cut here ]------------