cpufreq: intel_pstate: Fix NULL pointer dereference in update_cpu_qos_request()

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

cpufreq: intel_pstate: Fix NULL pointer dereference in update_cpu_qos_request()

The update_cpu_qos_request() function attempts to initialize the 'freq'

variable by dereferencing 'cpudata' before verifying if the 'policy'

is valid.

This issue occurs on systems booted with the "nosmt" parameter, where

all_cpu_data[cpu] is NULL for the SMT sibling threads. As a result,

any call to update_qos_requests() will result in a NULL pointer

dereference as the code will attempt to access pstate.turbo_freq using

the NULL cpudata pointer.

Also, pstate.turbo_freq may be updated by intel_pstate_get_hwp_cap()

after initializing the 'freq' variable, so it is better to defer the

'freq' until intel_pstate_get_hwp_cap() has been called.

Fix this by deferring the 'freq' assignment until after the policy and

driver_data have been validated.

[ rjw: Added one paragraph to the changelog ]