x86/PCI: Prevent mmconfig memory corruption
x86/PCI: Prevent mmconfig memory corruption

commit ff097ddd4 (x86/PCI: MMCONFIG: manage pci_mmcfg_region as a
list, not a table) introduced a nasty memory corruption when
pci_mmcfg_list is empty.

pci_mmcfg_check_end_bus_number() dereferences pci_mmcfg_list.prev even
when the list is empty. The following write hits some variable near to
pci_mmcfg_list.

Further down a similar problem exists, where cfg->list.next is
dereferenced unconditionally and a comparison with some variable near
to pci_mmcfg_list happens.

Add a check for the last element into the for_each_entry() loop and
remove all the other crappy logic which is just a leftover of the old
array based code which was replaced by the list conversion.

Reported-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>
Signed-off-by: Thomas Gleixner <00e4cf8f46a57000a44449bf9dd8cbbcc209fd2a@linutronix.de>
Cc: Bjorn Helgaas <10beeee9ebfac68af8330145c8378a1d1bb2a283@hp.com>
Cc: Yinghai Lu <0674548f4d596393408a51d6287a76ebba2f42aa@kernel.org>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@kernel.org
Signed-off-by: Jesse Barnes <bc7add126c2dbb8382bf1c28ac262b9363a32706@virtuousgeek.org>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas