Linux kernel sk_psock_get refcount bug due to sk_user_data type confusion

CVE-2022-49979 is a Linux kernel networking flaw in the interaction between SMC fallback handling and psock lookup logic. During the SMC fallback process in connect(), the kernel may replace TCP with SMC and set clcsk->sk_user_data to reference the original SMC socket in smc_fback_replace_callbacks() so wakeups can be forwarded after fallback. Later, during shutdown(), sk_psock_get() may be called and incorrectly interpret that same sk_user_data field as a psock pointer. Because both SMC and psock reuse sk_user_data, the field can be misclassified, leading sk_psock_get() to operate on an object of the wrong type and trigger refcount corruption warnings such as refcount saturation and memory leakage. The fix introduces an explicit SK_USER_DATA_PSOCK tag bit in the PTRMASK scheme so the kernel can distinguish whether sk_user_data actually points to a psock object before taking a reference.