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

commit 338c7dbadd2671189cec7faf64c84d01071b3f96 upstream.

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>
Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 302681c4aa44..eb99458f5b68 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1904,6 +1904,9 @@ 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);