KVM: Improve create VCPU parameter (CVE-2013-4587)

CVE-2013-4587

BugLink: http://bugs.launchpad.net/bugs/1261564

In multiple functions the vcpu_id is used as an offset into a bitfield.  Ag
malicious user could specify a vcpu_id greater than 255 in order to set or
clear bits in kernel memory.  This could be used to elevate priveges in the
kernel.  This patch verifies that the vcpu_id provided is less than 255.
The api documentation already specifies that the vcpu_id must be less than
max_vcpus, but this is currently not checked.

Reported-by: Andrew Honig <[email protected]>
Cc: [email protected]
Signed-off-by: Andrew Honig <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
(cherry picked from commit 338c7dbadd2671189cec7faf64c84d01071b3f96)
Acked-by: Brad Figg <[email protected]>
Signed-off-by: Luis Henriques <[email protected]>
Signed-off-by: Tim Gardner <[email protected]>

Author: Andy Honig

virt/kvm/kvm_main.c

@@ -1871,6 +1871,9 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 	int r;
 	struct kvm_vcpu *vcpu, *v;
 
+	if (id >= KVM_MAX_VCPUS)
+		return -EINVAL;
+
 	vcpu = kvm_arch_vcpu_create(kvm, id);
 	if (IS_ERR(vcpu))
 		return PTR_ERR(vcpu);