linux-kernel - Re: Re: [PATCH] fix memory leak on kvm_vm_ioctl_create_spapr

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Date:   Mon, 28 Aug 2017 16:06:30 +1000
From:   Paul Mackerras <paulus@...abs.org>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Nixiaoming <nixiaoming@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        "agraf@...e.com" <agraf@...e.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "kvm-ppc@...r.kernel.org" <kvm-ppc@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] fix memory leak on kvm_vm_ioctl_create_spapr_tce

On Mon, Aug 28, 2017 at 06:28:08AM +0100, Al Viro wrote:
> On Mon, Aug 28, 2017 at 02:38:37PM +1000, Paul Mackerras wrote:
> > On Sun, Aug 27, 2017 at 10:02:20PM +0100, Al Viro wrote:
> > > On Wed, Aug 23, 2017 at 04:06:24PM +1000, Paul Mackerras wrote:
> > > 
> > > > It seems to me that it would be better to do the anon_inode_getfd()
> > > > call before the kvm_get_kvm() call, and go to the fail label if it
> > > > fails.
> > > 
> > > And what happens if another thread does close() on the (guessed) fd?
> > 
> > Chaos ensues, but mostly because we don't have proper mutual exclusion
> > on the modifications to the list.  I'll add a mutex_lock/unlock to
> > kvm_spapr_tce_release() and move the anon_inode_getfd() call inside
> > the mutex.
> > 
> > It looks like the other possible uses of the fd (mmap, and passing it
> > as a parameter to the KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE ioctl on a KVM
> > device fd) are safe.
> 
> Frankly, it's a lot saner to have "no failure points past anon_inode_getfd()"
> policy...

Right.  In my latest patch, there are no failure points past
anon_inode_getfd().

Paul.