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

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Message-ID: <20210113072104.GH4678@unreal>
Date:   Wed, 13 Jan 2021 09:21:04 +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 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