linux-kernel - RE: [PATCH v2] ide: Check for null pointer after calling devm

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Date:   Fri, 7 Jan 2022 09:28:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jiasheng Jiang' <jiasheng@...as.ac.cn>,
        "damien.lemoal@...nsource.wdc.com" <damien.lemoal@...nsource.wdc.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2] ide: Check for null pointer after calling devm_ioremap

From: Jiasheng Jiang
> Sent: 07 January 2022 09:12
> 
> In linux-stable-5.15.13, this file has been removed and combined
> to `drivers/ata/pata_platform.c` without this bug.
> But in the older LTS kernels, like 5.10.90, this bug still exists.
> As the possible failure of the devres_alloc(), the devm_ioremap() and
> devm_ioport_map() may return NULL pointer.
> And then, the 'base' and 'alt_base' are used in plat_ide_setup_ports().
> Therefore, it should be better to add the check in order to avoid the
> dereference of the NULL pointer.
> Actually, it introduced the bug from commit 8cb1f567f4c0
> ("ide: Platform IDE driver") and we can know from the commit message
> that it tended to be similar to the `drivers/ata/pata_platform.c`.
> But actually, even the first time pata_platform was built,
> commit a20c9e820864 ("[PATCH] ata: Generic platform_device libata driver"),
> there was no the bug, as there was a check after the ioremap().
> So possibly the bug was caused by ide itself.
> 
> Fixes: 8cb1f567f4c0 ("ide: Platform IDE driver")
> Cc: stable@...r.kernel.org#5.10.90
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
> Changelog
> 
> v1 -> v2
> 
> * Change 1. Correct the fixes tag and commit message.
> ---
>  drivers/ide/ide_platform.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/ide/ide_platform.c b/drivers/ide/ide_platform.c
> index 91639fd6c276..5500c5afb3ca 100644
> --- a/drivers/ide/ide_platform.c
> +++ b/drivers/ide/ide_platform.c
> @@ -85,6 +85,10 @@ static int plat_ide_probe(struct platform_device *pdev)
>  		alt_base = devm_ioport_map(&pdev->dev,
>  			res_alt->start, resource_size(res_alt));
>  	}
> +	if (!base || !!alt_base) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}

That !!alt_base doesn't look right.
Without looking at the rest of the code maybe:
	if (!base && !alt_base)
may be correct.

It also rather makes me wonder about the actual failure return value.
If devm_ioport_map() returns a 'port number' for inb()/outb() then
zero is technically a valid value!

	David

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