Messages in this thread | | | Subject | Re: [PATCH v4 1/2] s390/vfio-ap: fix memory leak in mdev remove callback | From | Tony Krowiak <> | Date | Tue, 25 May 2021 09:22:02 -0400 |
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On 5/25/21 9:03 AM, Halil Pasic wrote: > On Fri, 21 May 2021 15:36:47 -0400 > Tony Krowiak <akrowiak@linux.ibm.com> wrote: > >> The mdev remove callback for the vfio_ap device driver bails out with >> -EBUSY if the mdev is in use by a KVM guest. The intended purpose was >> to prevent the mdev from being removed while in use; however, returning a >> non-zero rc does not prevent removal. This could result in a memory leak >> of the resources allocated when the mdev was created. In addition, the >> KVM guest will still have access to the AP devices assigned to the mdev >> even though the mdev no longer exists. >> >> To prevent this scenario, cleanup will be done - including unplugging the >> AP adapters, domains and control domains - regardless of whether the mdev >> is in use by a KVM guest or not. >> >> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") >> Cc: stable@vger.kernel.org >> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> >> Reviewed-by: Cornelia Huck <cohuck@redhat.com> > AFAIU we all agree that, after patch there is a possibility for an use > after free error.
I am assuming here that you meant to say that after applying patch 1/2, there is a possibility for a use after free error.
> I'm a little confused by the fact that we want this > one for stable, but the patch that fixes the use after free as no > Cc stable (it can't have a proper fixes tag, because this one is not yet > merged). Actually I'm not a big fan of splitting up patches to the > extent that when not all patches of the series are applied we get bugous > behavior (e.g. patch n breaks something that is live at patch n level, > but it is supposed to be OK, because patch n+m is going to fix it (where > n,m \in \Z^{+}). > > Do we want to squash these? Is the use after free possible prior to this > patch?
I am fine with squashing these if that is the consensus here. Prior to this patch, the remove callback function returned -EBUSY if a guest is still using the matrix_mdev (i.e., matrix_mdev->kvm not NULL), so the matrix_mdev was not freed and hence the memory leak for this this patch was designed to fix.
> > Regards, > Halil
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