CVE-2024-56640: 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.

refcountt: addition on 0; use-after-free. WARNING: CPU: 14 PID: 107447 at lib/refcount.c:25 refcountwarnsaturate+0x9c/0x140 Workqueue: events smclgrterminatework [smc] Call trace: refcountwarnsaturate+0x9c/0x140 smclgrterminate.part.45+0x2a8/0x370 [smc] smclgrterminatework+0x28/0x30 [smc] processonework+0x1b8/0x420 workerthread+0x158/0x510 kthread+0x114/0x118

or

refcountt: underflow; use-after-free. WARNING: CPU: 6 PID: 93140 at lib/refcount.c:28 refcountwarnsaturate+0xf0/0x140 Workqueue: smchswq smclistenwork [smc] Call trace: refcountwarnsaturate+0xf0/0x140 smcrlinkput+0x1cc/0x1d8 [smc] smcconnfree+0x110/0x1b0 [smc] smcconnabort+0x50/0x60 [smc] smclistenfinddevice+0x75c/0x790 [smc] smclistenwork+0x368/0x8a0 [smc] processonework+0x1b8/0x420 workerthread+0x158/0x510 kthread+0x114/0x118

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

e.g.

Calls under socklock | smclistenwork ------------------------------------------------------- locksock(sk) | smcconnabort smcconnfree | \- smcconnfree \- smcrlinkput | \- smcrlinkput (duplicated) releasesock(sk)

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