linux-kernel - Re: [PATCH v1] sysfs: fix sysfs_kf_seq

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Date:   Wed, 15 Jun 2022 19:53:30 +0200
From:   Christoph Hellwig <hch@....de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Will McVicker <willmcvicker@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, Tejun Heo <tj@...nel.org>,
        kernel-team@...roid.com, Christoph Hellwig <hch@....de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] sysfs: fix sysfs_kf_seq_show null pointer
 dereference

On Tue, Jun 14, 2022 at 07:28:31PM +0200, Greg Kroah-Hartman wrote:
> On Tue, Jun 14, 2022 at 05:24:01PM +0000, Will McVicker wrote:
> > When the kobj->ktype is null,
> 
> How can that happen?  What in-tree code does that?

Yes, I'd be really curious how we arrived there.  I we ever end in
this case we're having a major problem, as all the sysfs files
should go through sysfs_add_file_mode_ns, which already derferences
kobj->ktype->sysfs_ops directly.  I.e. for this to happen
kobj->ktype must have been cleared on a live file, or someone
must have bypassed sysfs_add_file_mode_ns.