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

[Vitaly Kuznetsov]

Rustam Kovhaev <rkovhaev@xxxxxxxxx> writes:

> 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
>

Personally, I'd prefer to make struct_size()/flex_array_size() a
separate preparatory patch so the real fix is small but I don't have a
strong opinion. I'll take look at v3 so feel free to drop R-b if you
decide to make a combined patch and feel free to keep it if you make the
preparatory changes separate :-)

-- 
Vitaly