From: Miklos Szeredi <mszeredi@redhat.com>
Date: Wed, 18 Jul 2018 15:44:43 +0200
Subject: [PATCH] vfs: fix freeze protection in mnt_want_write_file() for
 overlayfs
Git-commit: a6795a585929d94ca3e931bc8518f8deb8bbe627
Patch-mainline: v4.19-rc1
References: git-fixes

The underlying real file used by overlayfs still contains the overlay path.
This results in mnt_want_write_file() calls by the filesystem getting
freeze protection on the wrong inode (the overlayfs one instead of the real
one).

Fix by using file_inode(file)->i_sb instead of file->f_path.mnt->mnt_sb.

Reported-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/namespace.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -441,10 +441,10 @@ int mnt_want_write_file(struct file *fil
 {
 	int ret;
 
-	sb_start_write(file->f_path.mnt->mnt_sb);
+	sb_start_write(file_inode(file)->i_sb);
 	ret = __mnt_want_write_file(file);
 	if (ret)
-		sb_end_write(file->f_path.mnt->mnt_sb);
+		sb_end_write(file_inode(file)->i_sb);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_want_write_file);
@@ -486,7 +486,8 @@ void __mnt_drop_write_file(struct file *
 
 void mnt_drop_write_file(struct file *file)
 {
-	mnt_drop_write(file->f_path.mnt);
+	__mnt_drop_write_file(file);
+	sb_end_write(file_inode(file)->i_sb);
 }
 EXPORT_SYMBOL(mnt_drop_write_file);