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

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 <ahonig@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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1 parent 2e7babf commit 338c7dbadd2671189cec7faf64c84d01071b3f96 Andy Honig committed with bonzini Nov 19, 2013
Showing with 3 additions and 0 deletions.
  1. +3 −0 virt/kvm/kvm_main.c
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@@ -1898,6 +1898,9 @@ 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);

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