linux-kernel - Re: [PATCH] software node: Prevent link creation failure from causing kobj reference count imbalance

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Message-ID: <Z_ypLhYQwGf41hVK@smile.fi.intel.com>
Date: Mon, 14 Apr 2025 09:20:30 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Lizhi Xu <lizhi.xu@...driver.com>, Dmitry Vyukov <dvyukov@...gle.com>
Cc: syzbot+2ff22910687ee0dfd48e@...kaller.appspotmail.com, dakr@...nel.org,
	djrscally@...il.com, gregkh@...uxfoundation.org,
	heikki.krogerus@...ux.intel.com, jgg@...dia.com,
	kevin.tian@...el.com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, nicolinc@...dia.com,
	rafael@...nel.org, sakari.ailus@...ux.intel.com,
	syzkaller-bugs@...glegroups.com, yi.l.liu@...el.com
Subject: Re: [PATCH] software node: Prevent link creation failure from
 causing kobj reference count imbalance

On Fri, Apr 11, 2025 at 08:42:02AM +0800, Lizhi Xu wrote:
> syzbot reported a uaf in software_node_notify_remove. [1]
> 
> When any of the two sysfs_create_link() in software_node_notify() fails,
> the swnode->kobj reference count will not increase normally, which will
> cause swnode to be released incorrectly due to the imbalance of kobj reference
> count when executing software_node_notify_remove().
> 
> Increase the reference count of kobj before creating the link to avoid uaf.
> 
> [1]

Please, reduce this to ~5-7 lines only. This is how Submitting Patches document
recommends to put backtraces in the commit messages:
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#backtraces-in-commit-messages

> Fixes: 9eb59204d519 ("iommufd/selftest: Add set_dev_pasid in mock iommu")
> Reported-by: syzbot+2ff22910687ee0dfd48e@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2ff22910687ee0dfd48e

> Tested-by: syzbot+2ff22910687ee0dfd48e@...kaller.appspotmail.com

Where is the positive result of it? I can't find the respective log.
To me this one
https://syzkaller.appspot.com/x/report.txt?x=158af070580000
doesn't sound as a useful report as I don't know if this patch fixes one
regression and introduced another.

Dmitry?

-- 
With Best Regards,
Andy Shevchenko