linux-kernel - Re: [PATCH v5 3/4] KVM: arm64: Register ptdump with debugfs on guest creation

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Date: Tue, 13 Feb 2024 16:51:12 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Sebastian Ene <sebastianene@...gle.com>
Cc: catalin.marinas@....com, gshan@...hat.com, james.morse@....com,
	mark.rutland@....com, maz@...nel.org, rananta@...gle.com,
	ricarkol@...gle.com, ryan.roberts@....com, shahuang@...hat.com,
	suzuki.poulose@....com, will@...nel.org, yuzenghui@...wei.com,
	kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	vdonnefort@...gle.com
Subject: Re: [PATCH v5 3/4] KVM: arm64: Register ptdump with debugfs on guest
 creation

On Tue, Feb 13, 2024 at 04:42:27PM +0000, Sebastian Ene wrote:
> On Tue, Feb 13, 2024 at 12:56:20AM +0000, Oliver Upton wrote:
> > On Wed, Feb 07, 2024 at 02:48:32PM +0000, Sebastian Ene wrote:

[...]

> > > +static int kvm_ptdump_guest_open(struct inode *inode, struct file *file)
> > > +{
> > > +	return single_open(file, kvm_ptdump_guest_show, inode->i_private);
> > > +}
> > > +
> > 
> > Shouldn't we take a reference on the KVM struct at open to avoid UAF?
> > 
> > 	struct kvm *kvm = inode->i_private;
> > 
> > 	if (!kvm_get_kvm_safe(kvm))
> > 		return -ENOENT;
> > 
> > Then you can do a put on it at close().
> > 
> 
> Thanks, I though that the kvm_destroy_vm_debugfs will keep spinning if
> there are opened paths to the debugfs entry, but I guess nothing prevents
> that from happening and the kvm struct can be removed behind our back.

kvm_destroy_vm() will get called after the last put() on a kvm struct,
so all debugfs files should be closed too if we're consistent about
this.

-- 
Thanks,
Oliver