net/smc: fix LGR and link use-after-free issue
In the Linux kernel, the following vulnerability has been resolved:

net/smc: fix LGR and link use-after-free issue

We encountered a LGR/link use-after-free issue, which manifested as
the LGR/link refcnt reaching 0 early and entering the clear process,
making resource access unsafe.

 refcount_t: addition on 0; use-after-free.
 WARNING: CPU: 14 PID: 107447 at lib/refcount.c:25 refcount_warn_saturate+0x9c/0x140
 Workqueue: events smc_lgr_terminate_work [smc]
 Call trace:
  refcount_warn_saturate+0x9c/0x140
  __smc_lgr_terminate.part.45+0x2a8/0x370 [smc]
  smc_lgr_terminate_work+0x28/0x30 [smc]
  process_one_work+0x1b8/0x420
  worker_thread+0x158/0x510
  kthread+0x114/0x118

or

 refcount_t: underflow; use-after-free.
 WARNING: CPU: 6 PID: 93140 at lib/refcount.c:28 refcount_warn_saturate+0xf0/0x140
 Workqueue: smc_hs_wq smc_listen_work [smc]
 Call trace:
  refcount_warn_saturate+0xf0/0x140
  smcr_link_put+0x1cc/0x1d8 [smc]
  smc_conn_free+0x110/0x1b0 [smc]
  smc_conn_abort+0x50/0x60 [smc]
  smc_listen_find_device+0x75c/0x790 [smc]
  smc_listen_work+0x368/0x8a0 [smc]
  process_one_work+0x1b8/0x420
  worker_thread+0x158/0x510
  kthread+0x114/0x118

It is caused by repeated release of LGR/link refcnt. One suspect is that
smc_conn_free() is called repeatedly because some smc_conn_free() from
server listening path are not protected by sock lock.

e.g.

Calls under socklock        | smc_listen_work
-------------------------------------------------------
lock_sock(sk)               | smc_conn_abort
smc_conn_free               | \- smc_conn_free
\- smcr_link_put            |    \- smcr_link_put (duplicated)
release_sock(sk)

So here add sock lock protection in smc_listen_work() path, making it
exclusive with other connection operations.