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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Rustam Kovhaev <rkovhaev@gmail.com>
Cc:     linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org,
        pbonzini@redhat.com, kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: fix memory leak in kvm_io_bus_unregister_dev()
In-Reply-To: <20200830043405.268044-1-rkovhaev@gmail.com>
References: <20200830043405.268044-1-rkovhaev@gmail.com>
Date:   Tue, 01 Sep 2020 18:25:42 +0200
Message-ID: <877dtdwjjt.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Rustam Kovhaev <rkovhaev@gmail.com> writes:

> when kmalloc() fails in kvm_io_bus_unregister_dev(), before removing
> the bus, we should iterate over all other devices linked to it and call
> kvm_iodevice_destructor() for them
>
> Reported-and-tested-by: syzbot+f196caa45793d6374707@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?extid=f196caa45793d6374707
> Signed-off-by: Rustam Kovhaev <rkovhaev@gmail.com>
> ---
>  virt/kvm/kvm_main.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 67cd0b88a6b6..646aa7b82548 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4332,7 +4332,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
>  void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
>  			       struct kvm_io_device *dev)
>  {
> -	int i;
> +	int i, j;
>  	struct kvm_io_bus *new_bus, *bus;
>  
>  	bus = kvm_get_bus(kvm, bus_idx);
> @@ -4351,6 +4351,11 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
>  			  GFP_KERNEL_ACCOUNT);
>  	if (!new_bus)  {
                     ^^^ redundant space 

>  		pr_err("kvm: failed to shrink bus, removing it completely\n");
> +		for (j = 0; j < bus->dev_count; j++) {
> +			if (j == i)
> +				continue;
> +			kvm_iodevice_destructor(bus->range[j].dev);
> +		}
>  		goto broken;

The name of the label is really misleading (as it is not actually a
failure path), I'd even suggest we get rid of this goto completely,
something like

	new_bus = kmalloc(struct_size(bus, range, bus->dev_count - 1),
			  GFP_KERNEL_ACCOUNT);
	if (new_bus)  {
	       memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
	       new_bus->dev_count--;
	       memcpy(new_bus->range + i, bus->range + i + 1,
	              (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
        } else {
		pr_err("kvm: failed to shrink bus, removing it completely\n");
		for (j = 0; j < bus->dev_count; j++) {
			if (j == i)
				continue;
			kvm_iodevice_destructor(bus->range[j].dev);
	}

	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
	synchronize_srcu_expedited(&kvm->srcu);
	kfree(bus);
	return;


>  	}

None of the above should block the fix IMO, so:

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly