[PATCH] kernfs: fix NULL pointer dereference in __kernfs_new_node()

[PATCH] kernfs: fix NULL pointer dereference in __kernfs_new_node()

[Tejun Heo]

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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")
Cc: stable@vger.kernel.org
Reported-by: 杜义恒 <duyiheng@tju.edu.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 fs/kernfs/dir.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 5c0efd6b239f..29baeeb97871 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -681,8 +681,10 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 	return kn;

  err_out4:
-	simple_xattrs_free(&kn->iattr->xattrs, NULL);
-	kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
+	if (kn->iattr) {
+		simple_xattrs_free(&kn->iattr->xattrs, NULL);
+		kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
+	}
  err_out3:
 	spin_lock(&root->kernfs_idr_lock);
 	idr_remove(&root->ino_idr, (u32)kernfs_ino(kn));
--
2.47.2

Re: [PATCH] kernfs: fix NULL pointer dereference in __kernfs_new_node()

[Will Rosenberg]

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