CVE-2022-48751

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

net/smc: Transitional solution for clcsock race issue

We encountered a crash in smc_setsockopt() and it is caused by accessing smc->clcsock after clcsock was released.

BUG: kernel NULL pointer dereference, address: 0000000000000020 #PF: supervisor read access in kernel mode #PF: errorcode(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 1 PID: 50309 Comm: nginx Kdump: loaded Tainted: G E 5.16.0-rc4+ #53 RIP: 0010:smcsetsockopt+0x59/0x280 [smc] Call Trace: <TASK> __sys_setsockopt+0xfc/0x190 __x64syssetsockopt+0x20/0x30 dosyscall64+0x34/0x90 entrySYSCALL64afterhwframe+0x44/0xae RIP: 0033:0x7f16ba83918e </TASK>

This patch tries to fix it by holding clcsockreleaselock and checking whether clcsock has already been released before access.

In case that a crash of the same reason happens in smcgetsockopt() or smcswitchtofallback(), this patch also checkes smc->clcsock in them too. And the caller of smcswitchto_fallback() will identify whether fallback succeeds according to the return value.