Re: [PATCH] KVM: fix memory leak in kvm_io_bus_unregister_dev()

[Rustam Kovhaev]

On Tue, Sep 01, 2020 at 06:25:42PM +0200, Vitaly Kuznetsov wrote:
> Rustam Kovhaev <rkovhaev@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Link: https://syzkaller.appspot.com/bug?extid=f196caa45793d6374707
> > Signed-off-by: Rustam Kovhaev <rkovhaev@xxxxxxxxx>
> > ---
> >  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@xxxxxxxxxx>
> 
> -- 
> Vitaly
> 
hi Vitaly, thank you for the review! i'll send the new patch