linux-kernel - [PATCH AUTOSEL 4.18 06/92] vfs: fix freeze protection in mnt_want_write

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Date:   Sat, 15 Sep 2018 01:29:52 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Miklos Szeredi <mszeredi@...hat.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 06/92] vfs: fix freeze protection in
 mnt_want_write_file() for overlayfs

From: Miklos Szeredi <mszeredi@...hat.com>

[ Upstream commit a6795a585929d94ca3e931bc8518f8deb8bbe627 ]

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@...il.com>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 fs/namespace.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index bd2f4c68506a..1949e0939d40 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -446,10 +446,10 @@ int mnt_want_write_file_path(struct file *file)
 {
 	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;
 }
 
@@ -540,7 +540,8 @@ void __mnt_drop_write_file(struct file *file)
 
 void mnt_drop_write_file_path(struct file *file)
 {
-	mnt_drop_write(file->f_path.mnt);
+	__mnt_drop_write_file(file);
+	sb_end_write(file_inode(file)->i_sb);
 }
 
 void mnt_drop_write_file(struct file *file)
-- 
2.17.1