ovl: fix warning in ovl_create_real()

Syzbot triggered the following warning in ovl_workdir_create() -> ovl_create_real(): if (!err && WARN_ON(!newdentry->d_inode)) { The reason is that the cgroup2 filesystem returns from mkdir without instantiating the new dentry. Weird filesystems such as this will be rejected by overlayfs at a later stage during setup, but to prevent such a warning, call ovl_mkdir_real() directly from ovl_workdir_create() and reject this case early. Reported-and-tested-by: [email protected] Signed-off-by: Miklos Szeredi <[email protected]>
truenas · Nov 4, 2021 · 1f5573c · 1f5573c
1 parent 9a25440
commit 1f5573c
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Showing 3 changed files with 10 additions and 6 deletions.
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
@@ -137,8 +137,7 @@ int ovl_cleanup_and_whiteout(struct ovl_fs *ofs, struct inode *dir,
 	goto out;
 }
 
-static int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry,
-			  umode_t mode)
+int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry, umode_t mode)
 {
 	int err;
 	struct dentry *d, *dentry = *newdentry;

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
@@ -570,6 +570,7 @@ struct ovl_cattr {
 
 #define OVL_CATTR(m) (&(struct ovl_cattr) { .mode = (m) })
 
+int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry, umode_t mode);
 struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
 			       struct ovl_cattr *attr);
 int ovl_cleanup(struct inode *dir, struct dentry *dentry);

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
@@ -787,10 +787,14 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
 			goto retry;
 		}
 
-		work = ovl_create_real(dir, work, OVL_CATTR(attr.ia_mode));
-		err = PTR_ERR(work);
-		if (IS_ERR(work))
-			goto out_err;
+		err = ovl_mkdir_real(dir, &work, attr.ia_mode);
+		if (err)
+			goto out_dput;
+
+		/* Weird filesystem returning with hashed negative (kernfs)? */
+		err = -EINVAL;
+		if (d_really_is_negative(work))
+			goto out_dput;
 
 		/*
 		 * Try to remove POSIX ACL xattrs from workdir.  We are good if: