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Subject: Re: [PATCH v4] PCI: endpoint: Fix NULL pointer dereference for
 ->get_features()
To:     Shradha Todi <shradha.t@samsung.com>,
        <linux-kernel@vger.kernel.org>, <linux-pci@vger.kernel.org>
CC:     <bhelgaas@google.com>, <lorenzo.pieralisi@arm.com>,
        <pankaj.dubey@samsung.com>, <sriram.dash@samsung.com>,
        <niyas.ahmed@samsung.com>, <p.rajanbabu@samsung.com>,
        <l.mehra@samsung.com>, <hari.tv@samsung.com>
References: <CGME20210112140234epcas5p4f97e9cf12e68df9fb55d1270bd14280c@epcas5p4.samsung.com>
 <1610460145-14645-1-git-send-email-shradha.t@samsung.com>
From:   Kishon Vijay Abraham I <kishon@ti.com>
Message-ID: <b5b06656-913c-220d-3af7-bb9395252a7b@ti.com>
Date:   Wed, 13 Jan 2021 10:35:06 +0530
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On 12/01/21 7:32 pm, 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 ]---
> 
> Fixes: 2c04c5b8eef79 ("PCI: pci-epf-test: Use pci_epc_get_features() to get EPC features")
> Reviewed-by: Pankaj Dubey <pankaj.dubey@samsung.com>
> Signed-off-by: Sriram Dash <sriram.dash@samsung.com>
> Signed-off-by: Shradha Todi <shradha.t@samsung.com>

Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>
> ---
>  drivers/pci/endpoint/functions/pci-epf-test.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> index e4e51d8..1b30774 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -830,13 +830,16 @@ static int pci_epf_test_bind(struct pci_epf *epf)
>  		return -EINVAL;
>  
>  	epc_features = pci_epc_get_features(epc, epf->func_no);
> -	if (epc_features) {
> -		linkup_notifier = epc_features->linkup_notifier;
> -		core_init_notifier = epc_features->core_init_notifier;
> -		test_reg_bar = pci_epc_get_first_free_bar(epc_features);
> -		pci_epf_configure_bar(epf, epc_features);
> +	if (!epc_features) {
> +		dev_err(&epf->dev, "epc_features not implemented\n");
> +		return -EOPNOTSUPP;
>  	}
>  
> +	linkup_notifier = epc_features->linkup_notifier;
> +	core_init_notifier = epc_features->core_init_notifier;
> +	test_reg_bar = pci_epc_get_first_free_bar(epc_features);
> +	pci_epf_configure_bar(epf, epc_features);
> +
>  	epf_test->test_reg_bar = test_reg_bar;
>  	epf_test->epc_features = epc_features;
>  
>