cpufreq: qcom: fix writes in read-only memory region

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

cpufreq: qcom: fix writes in read-only memory region

This commit fixes a kernel oops because of a write in some read-only memory:

[ 9.068287] Unable to handle kernel write to read-only memory at virtual address ffff800009240ad8 ..snip.. [ 9.138790] Internal error: Oops: 9600004f [#1] PREEMPT SMP ..snip.. [ 9.269161] Call trace: [ 9.276271] __memcpy+0x5c/0x230 [ 9.278531] snprintf+0x58/0x80 [ 9.282002] qcom_cpufreq_msm8939_name_version+0xb4/0x190 [ 9.284869] qcom_cpufreq_probe+0xc8/0x39c ..snip..

The following line defines a pointer that point to a char buffer stored in read-only memory:

char *pvs_name = "speedXX-pvsXX-vXX";

This pointer is meant to hold a template "speedXX-pvsXX-vXX" where the XX values get overridden by the qcom_cpufreq_krait_name_version function. Since the template is actually stored in read-only memory, when the function executes the following call we get an oops:

snprintf(*pvs_name, sizeof("speedXX-pvsXX-vXX"), "speed%d-pvs%d-v%d", speed, pvs, pvs_ver);

To fix this issue, we instead store the template name onto the stack by using the following syntax:

char pvs_name_buffer[] = "speedXX-pvsXX-vXX";

Because the pvs_name needs to be able to be assigned to NULL, the template buffer is stored in the pvs_name_buffer and not under the pvs_name variable.