CVE-2022-48721

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

net/smc: Forward wakeup to smc socket waitqueue after fallback

When we replace TCP with SMC and a fallback occurs, there may be some socket waitqueue entries remaining in smc socket->wq, such as eppoll_entries inserted by userspace applications.

After the fallback, data flows over TCP/IP and only clcsocket->wq will be woken up. Applications can't be notified by the entries which were inserted in smc socket->wq before fallback. So we need a mechanism to wake up smc socket->wq at the same time if some entries remaining in it.

The current workaround is to transfer the entries from smc socket->wq to clcsock->wq during the fallback. But this may cause a crash like this:

general protection fault, probably for non-canonical address 0xdead000000000100: 0000 [#1] PREEMPT SMP PTI CPU: 3 PID: 0 Comm: swapper/3 Kdump: loaded Tainted: G E 5.16.0+ #107 RIP: 0010:__wakeupcommon+0x65/0x170 Call Trace: <IRQ> __wakeupcommonlock+0x7a/0xc0 sockdefreadable+0x3c/0x70 tcpdataqueue+0x4a7/0xc40 tcprcvestablished+0x32f/0x660 ? skfiltertrimcap+0xcb/0x2e0 tcpv4dorcv+0x10b/0x260 tcpv4rcv+0xd2a/0xde0 ipprotocoldeliverrcu+0x3b/0x1d0 iplocaldeliverfinish+0x54/0x60 iplocaldeliver+0x6a/0x110 ? tcpv4earlydemux+0xa2/0x140 ? tcpv4earlydemux+0x10d/0x140 ipsublistrcvfinish+0x49/0x60 ipsublistrcv+0x19d/0x230 iplistrcv+0x13e/0x170 __netifreceiveskb_listcore+0x1c2/0x240 netifreceiveskblistinternal+0x1e6/0x320 napicompletedone+0x11d/0x190 mlx5enapipoll+0x163/0x6b0 [mlx5core] __napipoll+0x3c/0x1b0 netrx_action+0x27c/0x300 __dosoftirq+0x114/0x2d2 irqexitrcu+0xb4/0xe0 commoninterrupt+0xba/0xe0 </IRQ> <TASK>

The crash is caused by privately transferring waitqueue entries from smc socket->wq to clcsock->wq. The owners of these entries, such as epoll, have no idea that the entries have been transferred to a different socket wait queue and still use original waitqueue spinlock (smc socket->wq.wait.lock) to make the entries operation exclusive, but it doesn't work. The operations to the entries, such as removing from the waitqueue (now is clcsock->wq after fallback), may cause a crash when clcsock waitqueue is being iterated over at the moment.

This patch tries to fix this by no longer transferring wait queue entries privately, but introducing own implementations of clcsock's callback functions in fallback situation. The callback functions will forward the wakeup to smc socket->wq if clcsock->wq is actually woken up and smc socket->wq has remaining entries.