linux-kernel - [PATCH MANUALSEL 5.18 6/6] KVM: Don't null dereference ops->destroy

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Message-Id: <20220614021116.1101331-6-sashal@kernel.org>
Date:   Mon, 13 Jun 2022 22:11:15 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Alexey Kardashevskiy <aik@...abs.ru>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>, kvm@...r.kernel.org
Subject: [PATCH MANUALSEL 5.18 6/6] KVM: Don't null dereference ops->destroy

From: Alexey Kardashevskiy <aik@...abs.ru>

[ Upstream commit e8bc2427018826e02add7b0ed0fc625a60390ae5 ]

A KVM device cleanup happens in either of two callbacks:
1) destroy() which is called when the VM is being destroyed;
2) release() which is called when a device fd is closed.

Most KVM devices use 1) but Book3s's interrupt controller KVM devices
(XICS, XIVE, XIVE-native) use 2) as they need to close and reopen during
the machine execution. The error handling in kvm_ioctl_create_device()
assumes destroy() is always defined which leads to NULL dereference as
discovered by Syzkaller.

This adds a checks for destroy!=NULL and adds a missing release().

This is not changing kvm_destroy_devices() as devices with defined
release() should have been removed from the KVM devices list by then.

Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 virt/kvm/kvm_main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5ab12214e18d..24cb37d19c63 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4299,8 +4299,11 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
 		kvm_put_kvm_no_destroy(kvm);
 		mutex_lock(&kvm->lock);
 		list_del(&dev->vm_node);
+		if (ops->release)
+			ops->release(dev);
 		mutex_unlock(&kvm->lock);
-		ops->destroy(dev);
+		if (ops->destroy)
+			ops->destroy(dev);
 		return ret;
 	}

-- 
2.35.1