[PATCH] KVM: Prevent double-free on HPT resize commit path
david at gibson.dropbear.id.au
Tue Feb 28 11:56:55 AEDT 2017
On Wed, Feb 15, 2017 at 02:40:04PM +1100, David Gibson wrote:
> resize_hpt_release(), called once the HPT resize of a KVM guest is
> completed (successfully or unsuccessfully) free()s the state structure for
> the resize. It is currently not safe to call with a NULL pointer.
> However, one of the error paths in kvm_vm_ioctl_resize_hpt_commit() can
> invoke it with a NULL pointer. This will occur if userspace improperly
> invokes KVM_PPC_RESIZE_HPT_COMMIT without previously calling
> KVM_PPC_RESIZE_HPT_PREPARE, or if it calls COMMIT twice without an
> intervening PREPARE.
> To fix this potential crash bug - and maybe others like it, make it safe
> (and a no-op) to call resize_hpt_release() with a NULL resize pointer.
> Found by Dan Carpenter with a static checker.
> Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
Paul have you taken this one?
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 3 +++
> 1 file changed, 3 insertions(+)
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 013552f..72ccac2 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -1407,6 +1407,9 @@ static void resize_hpt_release(struct kvm *kvm, struct kvm_resize_hpt *resize)
> BUG_ON(kvm->arch.resize_hpt != resize);
> + if (!resize)
> + return;
> if (resize->hpt.virt)
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
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