net/smc: fix sleep-inside-lock in __smc_setsockopt() causing local DoS

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

net/smc: fix sleep-inside-lock in __smc_setsockopt() causing local DoS

A logic flaw in __smc_setsockopt() allows a local unprivileged user to

cause a Denial of Service (DoS) by holding the socket lock indefinitely.

The function __smc_setsockopt() calls copy_from_sockptr() while holding

lock_sock(sk). By passing a userfaultfd-monitored memory page (or

FUSE-backed memory on systems where unprivileged userfaultfd is disabled)

as the optval, an attacker can halt execution during the copy operation,

keeping the lock held.

Combined with asynchronous tear-down operations like shutdown(), this

exhausts the kernel wq (kworkers) and triggers the hung task watchdog.

[ 240.123456] INFO: task kworker/u8:2 blocked for more than 120 seconds.

[ 240.123489] Call Trace:

[ 240.123501] smc_shutdown+...

[ 240.123512] lock_sock_nested+...

This patch moves the user-space copy outside the lock_sock() critical

section to prevent the issue.