FAILED: patch "[PATCH] ovl: check that the parents of volatile/dirty are dirs" 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 e34d2ef818e4c7676d8d8e1bf43e6a1ed39efb2a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026110453-dock-echo-0d7a@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From e34d2ef818e4c7676d8d8e1bf43e6a1ed39efb2a Mon Sep 17 00:00:00 2001
From: Chris Mason <mason@kernel.org>
Date: Wed, 7 Oct 2026 10:15:11 +0000
Subject: [PATCH] ovl: check that the parents of volatile/dirty are dirs

An unprivileged user crashes the kernel by mounting overlayfs with the
volatile option.

A dentry that serves as the parent of a lookup must be a directory.
ovl_create_volatile_dirty() walks work/incompat/volatile/dirty by name,
and ovl_lookup_or_create() returns an existing entry whatever its type.
A file or a symlink that another task creates during the mount becomes
the parent of the next lookup, which calls a NULL ->lookup.

An unprivileged user mounted overlayfs with "volatile" in a user
namespace while a second process created a symlink named work/incompat,
and the mount task oopsed on a NULL ->lookup call.

Fix this by returning -ENOTDIR from ovl_lookup_or_create() when the
caller asked for a directory and the existing entry is a non-dir.

Fixes: c86243b090bc ("ovl: provide a mount option "volatile"")
Cc: stable@vger.kernel.org
Signed-off-by: Chris Mason <mason@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index bd0a3f9039d2..18f56d463572 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -621,16 +621,21 @@ cleanup_temp:
 
 static struct dentry *ovl_lookup_or_create(struct ovl_fs *ofs,
 					   struct dentry *parent,
-					   const char *name, umode_t mode)
+					   const char *name, bool is_dir)
 {
 	struct dentry *child;
 
 	child = ovl_start_creating_upper(ofs, parent, &QSTR(name));
 	if (!IS_ERR(child)) {
-		if (!child->d_inode)
+		if (!child->d_inode) {
 			child = ovl_create_real(ofs, parent, child,
 						&QSTR(name),
-						OVL_CATTR(mode));
+						OVL_CATTR(is_dir ? S_IFDIR :
+								   S_IFREG));
+		} else if (is_dir && !d_can_lookup(child)) {
+			end_creating(child);
+			child = ERR_PTR(-ENOTDIR);
+		}
 		end_creating_keep(child);
 	}
 	dput(parent);
@@ -652,7 +657,7 @@ static int ovl_create_volatile_dirty(struct ovl_fs *ofs)
 	const char *const *name = volatile_path;
 
 	for (ctr = ARRAY_SIZE(volatile_path); ctr; ctr--, name++) {
-		d = ovl_lookup_or_create(ofs, d, *name, ctr > 1 ? S_IFDIR : S_IFREG);
+		d = ovl_lookup_or_create(ofs, d, *name, ctr > 1);
 		if (IS_ERR(d))
 			return PTR_ERR(d);
 	}