KVM: coalesced_mmio: add bounds checking
The first/last indexes are typically shared with a user app. The app can change the 'last' index that the kernel uses to store the next result. This change sanity checks the index before using it for writing to a potentially arbitrary address. This fixes CVE-2019-14821. Cc: stable@vger.kernel.org Fixes: 5f94c174 ("KVM: Add coalesced MMIO support (common part)") Signed-off-by: Matt Delco <delco@chromium.org> Signed-off-by: Jim Mattson <jmattson@google.com> Reported-by: syzbot+983c866c3dd6efa3662a@syzkaller.appspotmail.com [Use READ_ONCE. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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