Re: [PATCH v2] KVM: fix memory leak in kvm_io_bus_unregister_dev()

[Rustam Kovhaev]

On Wed, Sep 02, 2020 at 06:34:11PM -0500, Gustavo A. R. Silva wrote:
> Hi,
> 
> On 9/2/20 17:57, Rustam Kovhaev wrote:
> > 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>
> > Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> 
> I think it's worthwhile to add a Fixes tag for this, too.
> 
> Please, see more comments below...
> 
> > ---
> > v2:
> > - remove redundant whitespace
> > - remove goto statement and use if/else
> > ---
> >  virt/kvm/kvm_main.c | 21 ++++++++++++---------
> >  1 file changed, 12 insertions(+), 9 deletions(-)
> > 
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 67cd0b88a6b6..cf88233b819a 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);
> > @@ -4349,17 +4349,20 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> >  
> >  	new_bus = kmalloc(struct_size(bus, range, bus->dev_count - 1),
> >  			  GFP_KERNEL_ACCOUNT);
> > -	if (!new_bus)  {
> > +	if (new_bus) {
> > +		memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
> 
> 				    ^^^
> It seems that you can use struct_size() here (see the allocation code above)...
> 
> > +		new_bus->dev_count--;
> > +		memcpy(new_bus->range + i, bus->range + i + 1,
> > +		       (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
> 
> 					   ^^^
> ...and, if possible, you can also use flex_array_size() here.
> 
> Thanks
> --
> Gustavo
> 
> > +	} else {
> >  		pr_err("kvm: failed to shrink bus, removing it completely\n");
> > -		goto broken;
> > +		for (j = 0; j < bus->dev_count; j++) {
> > +			if (j == i)
> > +				continue;
> > +			kvm_iodevice_destructor(bus->range[j].dev);
> > +		}
> >  	}
> >  
> > -	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));
> > -
> > -broken:
> >  	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
> >  	synchronize_srcu_expedited(&kvm->srcu);
> >  	kfree(bus);
> > 

hi Gustavo, thank you for the review, i'll send the new patch.
Vitaly, i think i will need to drop your "Reviewed-by", because there is
going to be a bit more changes