I copied strcasecmp() from userland to the kernel and it didn't worked!
I started to debug the problem and I find out that this line:
while (tolower(*us1) == tolower(*us2++)) {
was adding _3_ bytes to 'us2' pointer. Am I loosing my minds here?!...
No, in-kernel tolower() is a macro which uses its argument three times.
Bad tolower(9), no cookie.