linux-kernel - Re: [PATCH v4] PCI: endpoint: Fix NULL pointer dereference for ->get

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Date:   Wed, 20 Jan 2021 07:29:25 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Shradha Todi <shradha.t@...sung.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        bhelgaas@...gle.com, kishon@...com, lorenzo.pieralisi@....com,
        pankaj.dubey@...sung.com, sriram.dash@...sung.com,
        niyas.ahmed@...sung.com, p.rajanbabu@...sung.com,
        l.mehra@...sung.com, hari.tv@...sung.com
Subject: Re: [PATCH v4] PCI: endpoint: Fix NULL pointer dereference for
 ->get_features()

On Tue, Jan 19, 2021 at 03:25:10PM +0530, Shradha Todi wrote:
> > -----Original Message-----
> > From: Leon Romanovsky <leon@...nel.org>
> > Subject: Re: [PATCH v4] PCI: endpoint: Fix NULL pointer dereference for -
> > >get_features()
> >
> > On Tue, Jan 12, 2021 at 07:32:25PM +0530, Shradha Todi wrote:
> > > 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.
> > >
> > > When the patch is not applied and EPC features is not implemented in
> > > the platform driver, we see the following dump due to kernel NULL
> > > pointer dereference.
> > >
> > > [  105.135936] Call trace:
> > > [  105.138363]  pci_epf_test_bind+0xf4/0x388 [  105.142354]
> > > pci_epf_bind+0x3c/0x80 [  105.145817]  pci_epc_epf_link+0xa8/0xcc [
> > > 105.149632]  configfs_symlink+0x1a4/0x48c [  105.153616]
> > > vfs_symlink+0x104/0x184 [  105.157169]  do_symlinkat+0x80/0xd4 [
> > > 105.160636]  __arm64_sys_symlinkat+0x1c/0x24 [  105.164885]
> > > el0_svc_common.constprop.3+0xb8/0x170
> > > [  105.169649]  el0_svc_handler+0x70/0x88 [  105.173377]
> > > el0_svc+0x8/0x640 [  105.176411] Code: d2800581 b9403ab9 f9404ebb
> > > 8b394f60 (f9400400) [  105.182478] ---[ end trace a438e3c5a24f9df0
> > > ]---
> >
> >
> > Description and call trace don't correlate with the proposed code change.
> >
> > The code in pci_epf_test_bind() doesn't dereference epc_features, at least
> in
> > direct manner.
> >
> > Thanks
>
> Thanks for the review. Yes, you're right. The dereference does not happen in
> the pci_epf_test_bind() itself, but in pci_epf_test_alloc_space() being
> called within. We will update the line "causing NULL pointer dereference in
> pci_epf_test_bind function. " in the commit message to "causing NULL pointer
> dereference in pci_epf_test_alloc_space function. " Would that be good
> enough?

I have no idea, just saw that the rest of the code at least partially
prepared to deal with epc_features == NULL, maybe
pci_epf_test_alloc_space() should be update to handle epc_features == NULL.

Thanks

>