ovl: allocate a container struct ovl_file for ovl private context

Instead of using ->private_data to point at realfile directly, so
that we can add more context per ovl open file.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>

Author: amir73il

fs/overlayfs/dir.c

@@ -1323,6 +1323,7 @@ static int ovl_create_tmpfile(struct file *file, struct dentry *dentry,
 	const struct cred *old_cred, *new_cred = NULL;
 	struct path realparentpath;
 	struct file *realfile;
+	struct ovl_file *of;
 	struct dentry *newdentry;
 	/* It's okay to set O_NOATIME, since the owner will be current fsuid */
 	int flags = file->f_flags | OVL_OPEN_FLAGS;
@@ -1344,14 +1345,21 @@ static int ovl_create_tmpfile(struct file *file, struct dentry *dentry,
 	if (err)
 		goto out_revert_creds;
 
+	of = ovl_file_alloc(realfile);
+	if (!of) {
+		fput(realfile);
+		err = -ENOMEM;
+		goto out_revert_creds;
+	}
+
 	/* ovl_instantiate() consumes the newdentry reference on success */
 	newdentry = dget(realfile->f_path.dentry);
 	err = ovl_instantiate(dentry, inode, newdentry, false, file);
 	if (!err) {
-		file->private_data = realfile;
+		file->private_data = of;
 	} else {
 		dput(newdentry);
-		fput(realfile);
+		ovl_file_free(of);
 	}
 out_revert_creds:
 	ovl_revert_creds(old_cred);
@@ -1407,7 +1415,7 @@ static int ovl_tmpfile(struct mnt_idmap *idmap, struct inode *dir,
 put_realfile:
 	/* Without FMODE_OPENED ->release() won't be called on @file */
 	if (!(file->f_mode & FMODE_OPENED))
-		fput(file->private_data);
+		ovl_file_free(file->private_data);
 put_inode:
 	iput(inode);
 drop_write:

fs/overlayfs/file.c

@@ -89,10 +89,32 @@ static int ovl_change_flags(struct file *file, unsigned int flags)
 	return 0;
 }
 
+struct ovl_file {
+	struct file *realfile;
+};
+
+struct ovl_file *ovl_file_alloc(struct file *realfile)
+{
+	struct ovl_file *of = kzalloc(sizeof(struct ovl_file), GFP_KERNEL);
+
+	if (unlikely(!of))
+		return NULL;
+
+	of->realfile = realfile;
+	return of;
+}
+
+void ovl_file_free(struct ovl_file *of)
+{
+	fput(of->realfile);
+	kfree(of);
+}
+
 static int ovl_real_fdget_path(const struct file *file, struct fd *real,
 			       struct path *realpath)
 {
-	struct file *realfile = file->private_data;
+	struct ovl_file *of = file->private_data;
+	struct file *realfile = of->realfile;
 
 	real->word = (unsigned long)realfile;
 
@@ -144,6 +166,7 @@ static int ovl_open(struct inode *inode, struct file *file)
 	struct dentry *dentry = file_dentry(file);
 	struct file *realfile;
 	struct path realpath;
+	struct ovl_file *of;
 	int err;
 
 	/* lazy lookup and verify lowerdata */
@@ -166,15 +189,20 @@ static int ovl_open(struct inode *inode, struct file *file)
 	if (IS_ERR(realfile))
 		return PTR_ERR(realfile);
 
-	file->private_data = realfile;
+	of = ovl_file_alloc(realfile);
+	if (!of) {
+		fput(realfile);
+		return -ENOMEM;
+	}
+
+	file->private_data = of;
 
 	return 0;
 }
 
 static int ovl_release(struct inode *inode, struct file *file)
 {
-	fput(file->private_data);
-
+	ovl_file_free(file->private_data);
 	return 0;
 }
 
@@ -426,13 +454,13 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 
 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	struct file *realfile = file->private_data;
+	struct ovl_file *of = file->private_data;
 	struct backing_file_ctx ctx = {
 		.cred = ovl_creds(file_inode(file)->i_sb),
 		.accessed = ovl_file_accessed,
 	};
 
-	return backing_file_mmap(realfile, vma, &ctx);
+	return backing_file_mmap(of->realfile, vma, &ctx);
 }
 
 static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)

fs/overlayfs/overlayfs.h

@@ -863,6 +863,9 @@ int ovl_real_fileattr_set(const struct path *realpath, struct fileattr *fa);
 int ovl_fileattr_get(struct dentry *dentry, struct fileattr *fa);
 int ovl_fileattr_set(struct mnt_idmap *idmap,
 		     struct dentry *dentry, struct fileattr *fa);
+struct ovl_file;
+struct ovl_file *ovl_file_alloc(struct file *realfile);
+void ovl_file_free(struct ovl_file *of);
 
 /* copy_up.c */
 int ovl_copy_up(struct dentry *dentry);