ovl: fix missing upper fs freeze protection on copy up for ioctl

Generalize the helper ovl_open_maybe_copy_up() and use it to copy up file
with data before FS_IOC_SETFLAGS ioctl.

The FS_IOC_SETFLAGS ioctl is a bit of an odd ball in vfs, which probably
caused the confusion.  File may be open O_RDONLY, but ioctl modifies the
file.  VFS does not call mnt_want_write_file() nor lock inode mutex, but
fs-specific code for FS_IOC_SETFLAGS does.  So ovl_ioctl() calls
mnt_want_write_file() for the overlay file, and fs-specific code calls
mnt_want_write_file() for upper fs file, but there was no call for
ovl_want_write() for copy up duration which prevents overlayfs from copying
up on a frozen upper fs.

Fixes: dab5ca8 ("ovl: add lsattr/chattr support")
Cc: <stable@vger.kernel.org> # v4.19
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -909,14 +909,14 @@ static bool ovl_open_need_copy_up(struct dentry *dentry, int flags)
 	return true;
 }
 
-int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
+int ovl_maybe_copy_up(struct dentry *dentry, int flags)
 {
 	int err = 0;
 
-	if (ovl_open_need_copy_up(dentry, file_flags)) {
+	if (ovl_open_need_copy_up(dentry, flags)) {
 		err = ovl_want_write(dentry);
 		if (!err) {
-			err = ovl_copy_up_flags(dentry, file_flags);
+			err = ovl_copy_up_flags(dentry, flags);
 			ovl_drop_write(dentry);
 		}
 	}

fs/overlayfs/file.c

@@ -116,11 +116,10 @@ static int ovl_real_fdget(const struct file *file, struct fd *real)
 
 static int ovl_open(struct inode *inode, struct file *file)
 {
-	struct dentry *dentry = file_dentry(file);
 	struct file *realfile;
 	int err;
 
-	err = ovl_open_maybe_copy_up(dentry, file->f_flags);
+	err = ovl_maybe_copy_up(file_dentry(file), file->f_flags);
 	if (err)
 		return err;
 
@@ -390,7 +389,7 @@ static long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		if (ret)
 			return ret;
 
-		ret = ovl_copy_up_with_data(file_dentry(file));
+		ret = ovl_maybe_copy_up(file_dentry(file), O_WRONLY);
 		if (!ret) {
 			ret = ovl_real_ioctl(file, cmd, arg);
 

fs/overlayfs/overlayfs.h

@@ -421,7 +421,7 @@ extern const struct file_operations ovl_file_operations;
 int ovl_copy_up(struct dentry *dentry);
 int ovl_copy_up_with_data(struct dentry *dentry);
 int ovl_copy_up_flags(struct dentry *dentry, int flags);
-int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags);
+int ovl_maybe_copy_up(struct dentry *dentry, int flags);
 int ovl_copy_xattr(struct dentry *old, struct dentry *new);
 int ovl_set_attr(struct dentry *upper, struct kstat *stat);
 struct ovl_fh *ovl_encode_real_fh(struct dentry *real, bool is_upper);