[PATCH] KVM: Prevent double-free on HPT resize commit path

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 <redacted>
Signed-off-by: David Gibson <redacted>
---
 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)
 		kvmppc_free_hpt(&resize->hpt);
 

-- 
2.9.3

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 <redacted>
Signed-off-by: David Gibson <redacted>

Ping,

Paul have you taken this one?

-- 
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_!
http://www.ozlabs.org/~dgibson

On Tue, Feb 28, 2017 at 11:56:55AM +1100, David Gibson wrote:

On Wed, Feb 15, 2017 at 02:40:04PM +1100, David Gibson wrote:

quoted

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 <redacted>
Signed-off-by: David Gibson <redacted>

Ping,

Paul have you taken this one?

Yes, thanks, it's in Linus' tree now.

Paul.