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From:   "Sriram Dash" <sriram.dash@samsung.com>
To:     "'Kishon Vijay Abraham I'" <kishon@ti.com>,
        "'Shradha Todi'" <shradha.t@samsung.com>
Cc:     <lorenzo.pieralisi@arm.com>, <bhelgaas@google.com>,
        <pankaj.dubey@samsung.com>, <linux-pci@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
In-Reply-To: <a7a6a295-160a-94d6-09f9-63f783c8b28a@ti.com>
Subject: RE: [PATCH] PCI: endpoint: Fix NULL pointer dereference for
 ->get_features()
Date:   Thu, 2 Apr 2020 20:01:59 +0530
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References: <CGME20200311103443epcas5p2e97b8f3a8e52dc6f02eb551e0c97f132@epcas5p2.samsung.com>
        <20200311102852.5207-1-shradha.t@samsung.com>
        <000d01d5fdf3$55d43af0$017cb0d0$@samsung.com>
        <a7a6a295-160a-94d6-09f9-63f783c8b28a@ti.com>
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> From: Kishon Vijay Abraham I <kishon=40ti.com>
> Subject: Re: =5BPATCH=5D PCI: endpoint: Fix NULL pointer dereference for =
-
> >get_features()
>=20
> Hi Sriram,
>=20
> On 3/19/2020 7:06 PM, Sriram Dash wrote:
> >> From: Shradha Todi <shradha.t=40samsung.com>
> >> Subject: =5BPATCH=5D PCI: endpoint: Fix NULL pointer dereference for -
> >>> get_features()
> >>
> >> get_features ops of pci_epc_ops may return NULL, causing NULL pointer
> >> dereference in pci_epf_test_bind function. Let us add a check for
> >> pci_epc_feature pointer in pci_epf_test_bind before we access it to
> >> avoid any such NULL pointer dereference and return -ENOTSUPP in case
> >> pci_epc_feature is not found.
> >>
> >> Reviewed-by: Pankaj Dubey <pankaj.dubey=40samsung.com>
> >> Signed-off-by: Sriram Dash <sriram.dash=40samsung.com>
> >> Signed-off-by: Shradha Todi <shradha.t=40samsung.com>
> >> ---
> >
> > Hi Kishon,
> >
> > Any update on this?
>=20
> Don't we access epc_features only after checking if epc_features is not N=
ULL in
> pci_epf_test_bind() function? However we are accessing epc_features in
> multiple other functions all over pci-epf-test.

We access the epc_feature after checking the NULL condition in the bind fun=
ction.
However, we do not stop if the epc_feature is NULL and proceed for allocati=
on in the
pci_epf_test_alloc_space function, for example. During this allocation, we =
do not check
for NULL condition for epc_feature and hence, if any controller driver is n=
ot providing
the epc features, it will panic accessing epc_features.

>=20
> So the patch itself is correct though the commit log has to be fixed. You=
 should
> also check if all the endpoint controller drivers existing currently prov=
ides
> epc_features.

At the moment, there is no issue for existing controller drivers as I can s=
ee almost
all drivers are providing epc_features. But, this is not a mandatory featur=
e and some
controller drivers may not have epc_features implemented, may be in the nea=
r future.
But because we are dealing with the configfs, the application need not both=
er about
the driver details underneath.

IMO, the code should be fixed regardless and should not cause panic in any =
case.

>=20
> Thanks
> Kishon
> >
> >
> >>  drivers/pci/endpoint/functions/pci-epf-test.c =7C 15 +++++++++------
> >>  1 file changed, 9 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c
> >> b/drivers/pci/endpoint/functions/pci-epf-test.c
> >> index c9121b1b9fa9..af4537a487bf 100644
> >> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> >> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> >> =40=40 -510,14 +510,17 =40=40 static int pci_epf_test_bind(struct pci_=
epf *epf)
> >>  		return -EINVAL;
> >>
> >>  	epc_features =3D pci_epc_get_features(epc, epf->func_no);
> >> -	if (epc_features) =7B
> >> -		linkup_notifier =3D epc_features->linkup_notifier;
> >> -		msix_capable =3D epc_features->msix_capable;
> >> -		msi_capable =3D epc_features->msi_capable;
> >> -		test_reg_bar =3D pci_epc_get_first_free_bar(epc_features);
> >> -		pci_epf_configure_bar(epf, epc_features);
> >> +	if (=21epc_features) =7B
> >> +		dev_err(dev, =22epc_features not implemented=5Cn=22);
> >> +		return -ENOTSUPP;
> >>  	=7D
> >>
> >> +	linkup_notifier =3D epc_features->linkup_notifier;
> >> +	msix_capable =3D epc_features->msix_capable;
> >> +	msi_capable =3D epc_features->msi_capable;
> >> +	test_reg_bar =3D pci_epc_get_first_free_bar(epc_features);
> >> +	pci_epf_configure_bar(epf, epc_features);
> >> +
> >>  	epf_test->test_reg_bar =3D test_reg_bar;
> >>  	epf_test->epc_features =3D epc_features;
> >>
> >> --
> >> 2.17.1
> >
> >