linux-kernel - Re: [PATCH] kernfs: fix NULL pointer dereference in __kernfs_new

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Message-ID: <aX+QW0yMZwVL5Y4h@gmail.com>
Date: Sun, 1 Feb 2026 10:41:47 -0700
From: Will Rosenberg <whrosenb@....edu>
To: Tejun Heo <tj@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Oliver Rosenberg <olrose55@...il.com>,
	杜义恒 <duyiheng@....edu.cn>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] kernfs: fix NULL pointer dereference in
 __kernfs_new_node()

On Sun, Feb 01, 2026 at 07:05:50AM -1000, Tejun Heo wrote:
> Commit 382b1e8f30f7 ("kernfs: fix memory leak of kernfs_iattrs in
> __kernfs_new_node") introduced an err_out4 error path which frees iattr
> when security_kernfs_init_security() fails. However, iattr is only
> allocated by __kernfs_setattr() when the node has non-default uid/gid.
> If the node uses default ownership, iattr remains NULL, and
> security_kernfs_init_security() failure would cause a NULL pointer
> dereference when err_out4 tries to access kn->iattr->xattrs.
> 
> Add a NULL check before freeing iattr.
> 
> Fixes: 382b1e8f30f7 ("kernfs: fix memory leak of kernfs_iattrs in __kernfs_new_node")

Thank you for reporting the bug.

This bug has been fixed by Commit 2b742094582d ("fs/kernfs: null-ptr deref in simple_xattrs_free()").
Commit 382b1e8f30f7 ("kernfs: fix memory leak of kernfs_iattrs in __kernfs_new_node")
was also caught from entering any stable releases, so the bug should be
fixed on all active branches.

Please correct me if this bug has not been fully addressed.

--
Will Rosenberg