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

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Date:   Tue, 19 Jan 2021 15:25:10 +0530
From:   "Shradha Todi" <shradha.t@...sung.com>
To:     "'Leon Romanovsky'" <leon@...nel.org>
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()

> -----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?