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

From	David Gibson <david@gibson.dropbear.id.au>
Newsgroups	linux.kernel
Subject	[PATCH] KVM: Prevent double-free on HPT resize commit path
Date	2017-02-15 04:50 +0100
Message-ID	<taYLo-2sg-7@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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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@oracle.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 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

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[PATCH] KVM: Prevent double-free on HPT resize commit path David Gibson <david@gibson.dropbear.id.au> - 2017-02-15 04:50 +0100
  Re: [PATCH] KVM: Prevent double-free on HPT resize commit path David Gibson <david@gibson.dropbear.id.au> - 2017-02-28 02:30 +0100
    Re: [PATCH] KVM: Prevent double-free on HPT resize commit path Paul Mackerras <paulus@ozlabs.org> - 2017-02-28 13:10 +0100

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