FAILED: patch "[PATCH] ovl: hold a reference on the parent in readdir" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 16d319e12328acafeafd3eecdf09c46d7fb43452
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026110448-rebuild-overpower-e0e1@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 16d319e12328acafeafd3eecdf09c46d7fb43452 Mon Sep 17 00:00:00 2001
From: Chris Mason <mason@kernel.org>
Date: Wed, 7 Oct 2026 10:53:10 +0000
Subject: [PATCH] ovl: hold a reference on the parent in readdir

Listing a directory on an overlay uses a freed dentry and crashes the
kernel when a lookup moves the directory at the same time.

Code that can sleep may only use d_parent without a reference while
something stops a move of the dentry. ovl_iterate_real(),
ovl_need_adjust_d_ino() and ovl_cache_update() use the d_parent of the
listed directory and hold only the lock of that directory. When a
lookup finds the directory under another parent after a change to a
layer, d_splice_alias() moves it without that lock and drops its
reference on the old parent.

With a delay in ovl_iterate_real(), getdents64 on an overlay directory
raced a rename in the lower layer and a lookup that moved its dentry,
and after an rmdir of the old parent KASAN reported a use-after-free in
security_inode_getattr().

Fix this by using dget_parent() in the three functions.

Fixes: b5efccbe0a12 ("ovl: constant d_ino across copy up")
Cc: stable@vger.kernel.org
Signed-off-by: Chris Mason <mason@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
[amir: fix comments in ovl_need_adjust_d_ino()]
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index b875332107d3..45239ef63e8c 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -588,8 +588,8 @@ static int ovl_cache_update(const struct path *path, struct ovl_cache_entry *p,
 			goto get;
 		}
 		if (p->len == 2) {
-			/* we shall not be moved */
-			this = dget(dir->d_parent);
+			/* d_splice_alias() can move even a locked dir */
+			this = dget_parent(dir);
 			goto get;
 		}
 	}
@@ -818,6 +818,7 @@ static int ovl_iterate_real(struct file *file, struct dir_context *ctx)
 	struct dentry *dir = file->f_path.dentry;
 	struct ovl_fs *ofs = OVL_FS(dir->d_sb);
 	const struct ovl_layer *lower_layer = ovl_layer_lower(dir);
+	struct dentry *parent;
 	struct ovl_readdir_translate rdt = {
 		.ctx.actor = ovl_fill_real,
 		.ctx.count = ctx->count,
@@ -829,18 +830,26 @@ static int ovl_iterate_real(struct file *file, struct dir_context *ctx)
 	if (rdt.xinobits && lower_layer)
 		rdt.fsid = lower_layer->fsid;
 
-	if (OVL_TYPE_MERGE(ovl_path_type(dir->d_parent))) {
+	/*
+	 * The lock on dir does not stop d_splice_alias() from moving it to
+	 * another parent, which drops the reference dir holds on this one.
+	 */
+	parent = dget_parent(dir);
+	if (OVL_TYPE_MERGE(ovl_path_type(parent))) {
 		struct kstat stat;
 		struct path statpath = file->f_path;
 
-		statpath.dentry = dir->d_parent;
+		statpath.dentry = parent;
 		err = vfs_getattr(&statpath, &stat, STATX_INO, 0);
-		if (err)
+		if (err) {
+			dput(parent);
 			return err;
+		}
 
 		WARN_ON_ONCE(dir->d_sb->s_dev != stat.dev);
 		rdt.parent_ino = stat.ino;
 	}
+	dput(parent);
 
 	if (ovl_is_impure_dir(file)) {
 		rdt.cache = ovl_cache_get_impure(&file->f_path);
@@ -896,8 +905,10 @@ static bool ovl_need_adjust_d_ino(struct file *file)
 {
 	struct dentry *dentry = file->f_path.dentry;
 	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
+	struct dentry *parent;
+	enum ovl_path_type type;
 
-	/* If parent is merge, then need to adjust d_ino for '..' */
+	/* With xino, need to map real d_ino to the unified overlay ino space */
 	if (ovl_xino_bits(ofs))
 		return true;
 
@@ -906,8 +917,14 @@ static bool ovl_need_adjust_d_ino(struct file *file)
 		return false;
 
 	/* If dir is impure then need to adjust d_ino for copied up entries */
-	if (ovl_is_impure_dir(file) ||
-	    OVL_TYPE_MERGE(ovl_path_type(dentry->d_parent)))
+	if (ovl_is_impure_dir(file))
+		return true;
+
+	/* If parent is merge, then need to adjust d_ino for '..' */
+	parent = dget_parent(dentry);
+	type = ovl_path_type(parent);
+	dput(parent);
+	if (OVL_TYPE_MERGE(type))
 		return true;
 
 	/* Pure: no need to adjust d_ino */