ring-buffer: Fix possible dereference of uninitialized pointer

In the Linux kernel, the following vulnerability has been resolved: ring-buffer: Fix possible dereference of uninitialized pointer There is a pointer head_page in rb_meta_validate_events() which is not initialized at the beginning of a function. This pointer can be dereferenced if there is a failure during reader page validation. In this case the control is passed to "invalid" label where the pointer is dereferenced in a loop. To fix the issue initialize orig_head and head_page before calling rb_validate_buffer. Found by Linux Verification Center (linuxtesting.org) with SVACE.