CVE-2026-99006: drm/i915/gem: Prevent overstepping exec array boundary

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

drm/i915/gem: Prevent overstepping exec array boundary

It is possible for ebrelocateparseslow() to call kvfree() on entries outside the original exec array during following scenario inside ebrelocateparseslow():

1) ebcopyrelocations() allocates as many as eb->buffercount copies for exec entries; 2) ebparse() appends up to two VMAs, right after incrementing eb->buffercount; 3) cleanup under "out" label uses this incremented buffercount to release relocation pointers from exec array via kvfree(), not from VMA array.

To amend this problem, ensure that relocation cleanup uses the original exec object count, excluding the VMAs appended by the command parser.

(cherry picked from commit 2a0158925fb943c7ba8f3216e2734952128defc9)