FAILED: patch "[PATCH] ovl: check that the parents of volatile/dirty are dirs" failed to apply to 5.15-stable tree

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 <[email protected]>.

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 '<[email protected]>' --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 <[email protected]>
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.

index bd0a3f9039d2..18f56d463572 100644
@@ -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);
 	}

From: Chris Mason <[email protected]>

[ Upstream commit e34d2ef818e4c7676d8d8e1bf43e6a1ed39efb2a ]

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.

---
 fs/overlayfs/super.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

index 2ad1f8652ce61..6e97ef29ebd8c 100644
@@ -1321,16 +1321,23 @@ static int ovl_check_rename_whiteout(struct ovl_fs *ofs)
 
 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)
 {
 	size_t len = strlen(name);
 	struct dentry *child;
 
 	inode_lock_nested(parent->d_inode, I_MUTEX_PARENT);
 	child = lookup_one_len(name, parent, len);
-	if (!IS_ERR(child) && !child->d_inode)
-		child = ovl_create_real(ofs, parent->d_inode, child,
-					OVL_CATTR(mode));
+	if (!IS_ERR(child)) {
+		if (!child->d_inode) {
+			child = ovl_create_real(ofs, parent->d_inode, child,
+						OVL_CATTR(is_dir ? S_IFDIR :
+								   S_IFREG));
+		} else if (is_dir && !d_can_lookup(child)) {
+			dput(child);
+			child = ERR_PTR(-ENOTDIR);
+		}
+	}
 	inode_unlock(parent->d_inode);
 	dput(parent);
 

@@ -1351,7 +1358,7 @@ 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);
 	}

2.53.0